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Title: The Potter's Craft
A Practical Guide for the Studio and Workshop
Author: Charles F. Binns
Release Date: August 4, 2012 [EBook #40411]
Language: English
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[Illustration: _Frontispiece_ STONEWARE MADE BY THE AUTHOR.]
The Potter's Craft
A Practical Guide for the Studio and Workshop
_By_ CHARLES F. BINNS
_Director of the New York State School of Clay-Working
and Ceramics_ ¶ _Some time a Superintendent in the
Royal Porcelain Works, Worcester, England_
_SECOND EDITION_
_SECOND PRINTING_
_26 PLATES AND 20 TEXT ILLUSTRATIONS_
[Colophon]
NEW YORK
D. VAN NOSTRAND COMPANY, INC.
EIGHT WARREN STREET
Copyright, 1910, 1922
by
D. Van Nostrand Company
_All rights reserved, including that of translation
into the Scandinavian and other foreign languages._
Printed in the United States of America
LANCASTER PRESS, INC.
LANCASTER, PA.
"A book is written, not to multiply the
voice merely, not to carry it merely,
but to perpetuate it. The author has
something to say which he perceives to
be true and useful, or helpfully
beautiful. So far as he knows, no one
has yet said it; so far as he knows, no
one else can say it. He is bound to say
it clearly and melodiously if he may;
clearly, at all events."
--_Ruskin._
PREFACE TO SECOND EDITION
Since the publication of the first edition of this book eleven years
have elapsed, years packed full of varied and interesting experiences.
During that time it has been the pleasant fortune of the author to
conduct classes, especially summer classes, in the science and art of
pottery production. These have been occasions of meeting many fine and
noble personalities whom to know is a liberal education. As one of the
consequences of these experiences the book has been revised and some new
chapters have been written. Especial acknowledgments are due and are
gratefully made to Elsie Binns for the chapter on Clay-Working for
Children and to Maude Robinson for that on Alkaline Glazes.
The photographs are by the Taylor Studios, Hornell, N. Y.
C. F. B.
Alfred, New York.
March, 1922.
PREFACE TO FIRST EDITION
This Book is the outcome of an experience extending over a period of
thirty-six years. Twenty years ago it would have been impossible, for
the science of ceramics was not then born. Ten years ago it would have
been wasted for the Artist-potter in America had not arrived, but now
the individual workers are many and the science is well established.
Written teaching must be imperfect, but I have endeavored to set down
the exact methods by which my students are taught, in the hope that
those who cannot secure personal instruction may read and understand.
As far as possible didactic statements have been avoided and the attempt
has been made to lead every student to experiment and to think for
himself. In other words, I have tried to erect sign-posts and occasional
warnings rather than to remove all obstacles from the road.
C. F. B.
Alfred, N. Y.
January, 1910.
CONTENTS
Introduction.--The Present Need xiii
CHAPTER
I. Applied Art 1
II. Pottery 9
III. Porcelain 23
IV. The Nature and Properties of Clay 29
V. The Preparation of Clay 37
VI. Mold-Making and Plaster 43
VII. Cases and Working Molds 58
VIII. Building by Hand 68
IX. The Potter's Wheel 74
X. Turning 99
XI. Making Large Pieces 107
XII. Cups and Saucers and Plates 124
XIII. Casting 129
XIV. Tiles 133
XV. Glazes and Glazing
Part I 140
Part II--Matt Glazes 152
Part III--Fritted Glazes 157
Part IV--Recipes 160
Part V--The Defects of Glazes 164
Part VI--Alkaline Glazes 167
XVI. Decoration 173
XVII. The Fire 179
XVIII. High Temperature Wares 188
XIX. Clay-working for Children 194
INDEX 201
LIST OF PLATES
Frontispiece.--Stoneware made by the Author.
PLATE. PAGE
I. Throwing.--Lesson II, 1 80
II. Throwing.--Lesson II, 2 81
III. Throwing.--Lesson II, 3 82
IV. Throwing.--Lesson III, 1 83
V. Throwing.--Lesson III, 2 86
VI. Throwing.--Lesson IV, 1 87
VII. Throwing.--Lesson IV, 2 89
VIII. Throwing.--Lesson V 90
IX. Throwing.--Lesson VI, 1 92
X. Throwing.--Lesson VI, 2 93
XI. Throwing.--Lesson VII 95
XII. Throwing.--Lesson VIII, 1 96
XIII. Throwing.--Lesson VIII, 2 97
XIV. Making Large Pieces. The First Section 109
XV. Making Large Pieces. Measuring the Foundation of the 110
Second Section
XVI. Making Large Pieces. Drawing up the Second Section 111
XVII. Making Large Pieces. Shaping the Third Section 112
XVIII. Making Large Pieces. The Three Sections Completed 113
XIX. Making Large Pieces. Turning the Edge of the First 114
Section
XX. Making Large Pieces. Finishing the Bottom of the First 116
Section
XXI. Making Large Pieces. Checking the Size of the Second 117
Section
XXII. Making Large Pieces. Fitting Together Dry 119
XXIII. Making Large Pieces. Setting the Third Section in Place 120
XXIV. Making Large Pieces. The Three Sections Set Together in 121
the Rough
XXV. Making Large Pieces. The Finished Vase 122
INTRODUCTION: THE PRESENT NEED
Many times it has been proven, in the history of the world, that it is
not possible to force a reform or a novelty upon an unwilling people.
Such things are organic. In order to live they must grow and in order to
grow must live. No attempt will be made, therefore, in these pages to
foster an idea or propound a thought which may exist only in the
predilection of the author.
The trend of the present demand, a persistent growth of several years,
is towards a personal and individual expression in the crafts or
industrial arts. This tendency is the natural swing of the pendulum from
the machine-made product of the manufactory which in its turn was the
inevitable result of mechanical invention.
When the artisan was an artist and the designer a craftsman, there was
but a limited production of industrial art. The articles made were
expensive and for the wealthy alone. The common utensils necessary to
the household were made on the farm and were of the rudest possible
character. But with the gradual development of machinery there came an
abandonment of rural activities, a flocking to the city, manufacturing
on a large scale, lower prices, and a huge output. This has, of course,
taken many years to develop, but the utmost limit of the swing has been
reached and the question is "What next?" Will the factory cease its
labors? Will output decrease in bulk and improve in quality? Will there
ever, in a word, be a return to medieval conditions? Not only may all
these questions be answered in the negative but it may be stated with
all sincerity that there is no need for any other answer.
What then, are not manufactured products as now put forth a menace to
the art life of the nation? Are not the people being educated in the use
of and belief in machine-made ornament and meretricious display? Perhaps
so, but no good purpose will be served by a ruthless condemnation of
these things. Art appreciation is a most subtle thing and no one may
dictate to his neighbor as to what he should or should not admire. It
took time for the public to understand and patronize the product of the
machine even though the price was favorable. It will take time for an
appreciation of craftsmanship to influence the land but this
consummation will most assuredly come.
On the one hand there is the manufactory, teeming with "hands," riotous
with wheels, turning out its wares by the thousand and supplying the
demand of the many; on the other, there is the artist-artisan. He labors
at his bench in sincere devotion to his chosen vocation. His work is
laborious and exacting, he can make but a few things and for them he
must ask a price relatively high. Both these conditions are necessary.
The craftsman cannot supply the need of the people and the manufacturer
has no time or thought for disinterested production. Herein lies the
need and here is the mission of the individual worker.
In every age it is given to some to discern more than the multitude and
it is theirs to teach. The people are anxious to learn, are eager to be
led. What they demand will be manufactured and so by the irresistible
lever of public opinion the man at the bench, if he be true to himself
and to his craft, may move the millionaire manufacturer to make wares
which, if not truly artistic, shall at least be inoffensive. Such a
mission is not to be accomplished without suffering. The man who essays
to attack a giant must be sure both of his ground and of his personal
condition. He who would establish his craft in the knowledge and
affection of men must possess enthusiasm, skill, discrimination and
infinite patience.
It is not enough to discern the good, the hand must follow the brain
with diligent care. Furthermore, it is not enough to be able to make
things well, one must also make them good and know it. The
artist-artisan must have courage to destroy that which is below
standard, and self-denial to resist the temptation to sell an unworthy
product.
The country needs craftsmen of this type and for them there is an
important work. For such, if they elect to join the ranks of the
potters, these words are written and in the hope that some may be
stimulated, encouraged, guided and helped the counsel of a fellow
craftsman is offered.
CHAPTER I: APPLIED ART
It is not intended, in these lines, to consider what are generally
termed the Fine Arts, painting and sculpture. These are perfectly
competent to take care of themselves and, indeed, the author can make no
claim to an ability to discuss them. In the field of applied art,
however, there are certain principles to be observed, principles,
moreover, which are frequently lost sight of because of the lamentable
separation of the functions of the artist and artificer.
It is extremely difficult to draw the line between art and manufacture.
For example, a wall paper, designed with skill and executed by machinery
in actual reproduction of the work of the designer; is it a work of art
or is it a product of the factory? It is both. Primarily a work of art
is the product of the artist's own hand. It reveals his individuality.
It is the language in which he expresses himself to his audience. It is
the note of his voice. Such a work may or may not appeal to a large
section of the public. This will always be so. An artist, be he poet,
musician, painter or craftsman, is one who can see more than others.
What he sees he endeavors to express but it is inevitable that he be
sometimes misunderstood. Hence it the more necessary that his message be
delivered at first hand. To look upon a replica of the work of an artist
is like reading a sermon or an oration from a printed page. One may
gather much of the teaching but the personal note, the tone and gesture,
must be lost.
But there are many who can gather the words of great men only from
books. There are, moreover, books which have never been spoken and
wherein alone the message is to be found. In like manner there are
works, emanating from the hand of great designers which can only be made
available for the many in a form of reproduction. The wall paper cited
as an illustration is of this class. Were it not for the printing press
this beautiful design could not have passed beyond the studio, and while
it is a great thing if a wealthy man can commission a Whistler to
decorate a peacock room, it is an advantage by no means to be ignored
that a well designed wall paper can be purchased by the piece.
But while this is true of such of the household goods as cannot be
procured except by the medium of the machine, there are other examples.
In the case of the wall paper the function of the machine is simply to
transfer the proper design to the paper itself. This has no identity
except as a surface. It is no more to be considered than is a canvas
upon which a picture is painted. But when a chair or a table is formed
out of pieces of lumber uniformly shaped by one machine, the seat or top
put together by another and the legs or back carved or stamped by a
third, art or individuality is lost because mechanical construction is
involved.
Still more is this the case in the product of the manufactory of
pottery. In commercial practice not only is a shape designed without
regard to decoration but the same decoration is placed upon several
forms, or a single form is made to suffer as the vehicle for many
decorations. Some of the results may be pleasing, even beautiful, but it
is more by luck than guidance and no piece produced in this way has any
claim to be classed as a work of art.
On the other hand it may happen that a work of art, in the sense of
individual expression, may not even be beautiful and one is tempted to
ask the reason. If a work which is a genuine expression of a man's
personality fail to please the senses of those who are trained in the
finer perceptions there must be something wrong.
If the adverse opinion be at all general amongst the critics it may be
assumed that they are right and that the worker is wrong.
For example, the form of a flower is not a fit receptacle for a candle.
It often happens that a designer, struck with the beauty of, say, a
tulip, has modeled the flower in clay and made it into a candlestick.
Now it is obvious that the more closely the model simulates the flower
the less appropriate it is for such a purpose. If the model be heavy
enough to be of use it must be far removed from its prototype. If a
conventional design for a candlestick be adopted the petals of a flower
may be shown in relief upon it but there must always be a solid
foundation to account for the possibility of use.
A favorite form with some designers is a bird's nest made into a flower
holder. In this the same criticism applies. A bird's nest is always
built to let water escape. Even a mud-lined nest is not impervious and
the idea is obviously inappropriate. It is important that imitation be
avoided and especially the imitation of material. One often hears the
remark "How beautiful, it looks just like bronze." This, of course,
comes from the casual observer to whom the skill of the imitation
appeals but it cannot be too strongly insisted upon that to imitate one
material in another is false from every point of view. Nor is it
necessary. Clay is sufficient in itself. There are so many effects
possible in pottery which are not possible in any other medium that it
is entirely superfluous to seek outlandish texture and color. To be
sure, such things are popular but that does not make them sound in
principle or true in taste.
It should not be a purpose of any craft to make pieces merely as an
exhibition of skill. This is done sometimes by such versatile workers as
the Japanese, but it may be laid down as a law that a production of the
nature of a _tour-de-force_, an object which simply excites wonder at
the skill of the worker, is undignified and meretricious. It is akin to
the work of certain painters who delight in painting marble or velvet so
as to exhibit a perfect texture only and is but one degree removed from
the skill of the pavement artist who with colored chalk draws a lamb
chop or a banana in such a manner that the real article seems to be
lying on the ground at his feet.
The true artist, be he potter or painter, works primarily for his own
satisfaction. It sometimes happens that a defect, not large enough to be
obvious, is a temptation to concealment. The public will never know. But
the consciousness of the existence of such a blemish will destroy the
pride of achievement which should accompany every finished piece.
If the worker aims to draw any expression of opinion from the untrained
observer it should be in the nature of a remark on how easy the work
looks. Art will always conceal effort. Just as the poet or orator is at
his best when he clothes sublime thought in simple words so the artist
or craftsman glorifies his vocation when he makes use of means which
appear to be within the reach of every observer.
In addition to the work of the producer there must be considered the
function of the critic. Artists are commonly impatient of criticism.
Tennyson voiced this sentiment when he wrote of "Irresponsible indolent
reviewers," but the power of the critic is rarer than the skill of the
craftsman. True, there are critics and critics. There is the man who
knows what he likes and who cannot be persuaded that he likes what is
false, and there is the trained critic who sees with an educated eye and
dissects with an unerring word. It is not common to find critic and
craftsman in one and the same person and it not infrequently happens
that the persons exercising these functions are at variance with each
other.
But if the critic be correct why is the craftsman wrong? In this let it
be presumed that there is nothing wrong with his craft as such; that he
handles his tools skilfully and has perfect control over his material.
More than this, however, is necessary. The first requirement is a sense
of form, a term which includes outline, proportion and structure. Often
and often it is found that a designer depends upon novelty alone for
acceptance. He is not altogether to blame in this for the great American
public will, more often than not, ask, "Is it new?"
Novelty in itself is no claim to consideration; in fact, on being shown
some product of which it is said "Nothing like it has ever been seen
before," the temptation is great to respond, "May its like never be seen
again." Novelty apart, form must possess proportion, balance and grace.
A chair must invite the sitter, a vase must stand securely, a carpet
must lie flat. The absence of these things may evidence an individuality
on the part of the designer but it is art at the expense of truth.
The second necessary condition is fitness which again is expressed in
several ways. A porcelain vase is required to be light, graceful and
refined. A piece of ruder pottery may be no less satisfactory if it
exhibit vigor, strength and solidity. A large pot for a growing tree is,
for these reasons, more appropriate in grès than in porcelain. Porcelain
is translucent but such a quality is of no advantage in the case of a
flower pot; the strength of a massive body is, however, demanded by the
circumstances of use and hence the unfitness of the one and the fitness
of the other.
Another point of fitness is concerned in the correspondence between
size, form and weight. It often happens that one takes hold of a piece
of pottery and experiences a shock. The mind unconsciously forms an
estimate of what the weight will be but the piece does not respond. The
effort put forth in accordance with the appearance of the object either
lifts it suddenly into the air or fails to raise it from the table. The
artist critic takes note of these things. To handle his wares is a
constant pleasure, for one is not continually disappointed by unexpected
violences. This correspondence or equilibrium is apart from the use of a
piece of pottery. It is quite as legitimate to express one's ideas in
clay in the presentation of simple beauty as it is to express them with
paint upon canvas. At the same time there is always a satisfaction in a
vase or flower pot that it can be used if required. Thus a vase which
will not hold water is technically imperfect and the _bête noire_ of the
conscientious potter.
It is in the harmony of these things that the rôle of the critic is seen
to advantage. If the artist be capable of criticizing his own work he is
in a position to command attention but he must either discipline himself
or be disciplined by others, which, after all, is the way of the world
at large.
CHAPTER II: POTTER
It must always be an open question how much credit for artistic feeling
can be given to primitive races. The production of pottery was, at
first, the supplying of a need. Clay offered a medium for the making of
household utensils which were at once fireproof and impervious. The work
does not belong strictly to the earliest stages of civilization but is a
development of advancing refinement.[A]
[A] Those who wish to study Indian pottery in detail are referred to
Dr. W. H. Holmes' work on the Aboriginal Pottery of the Eastern
United States, published by the Smithsonian Institution,
Washington, D. C.
Crude and unprepared clays were used for the most part but the makers
could scarcely have been conscious of the charming color-play produced
by the burning of a red clay in a smoky fire. The pottery of the Indians
is artistic in the sense of being an expression of an indigenous art and
much of it is beautiful, though whether the makers possessed any real
appreciation of beauty is open to doubt.
The pottery was exclusively the work of the women. No wheel was employed
but the ware was mainly constructed by coiling. Long strips of clay were
rolled under the hands and made of uniform size and these were then
coiled in spiral form, the rolls being welded together with water. After
proceeding a certain height the walls of the growing jar would become
weak under their own weight. The piece would then be set aside to
undergo a partial hardening upon which the work would be carried forward
another stage. The shape being completed and partially dried, the maker
would work over the whole surface with stones or simple tools until the
marks of the coils had disappeared and the walls had reached a
sufficient thinness. A great deal of skill was exercised in
accomplishing this.
Many of the Indian forms are transitional. The basket, the gourd and the
bark-made jar suggested their shapes to the potter; indeed it is
sometimes evident that clay vessels were constructed as linings to
wicker forms, the outer layer of twigs being afterwards burned off. The
firing was performed in the open flame without any protection, a fact
which accounts for the great irregularity found in quality and color.
The decorations used by the Indian women were of the type common to
unglazed wares. The clay was incised or embossed and natural earths were
used as pigments. This accounts in great measure for the fitness which
may be observed in aboriginal decoration. There is an absence of
artificial coloring, nor is there any straining after effect, but
instead there is shown a sober strength and a sane expression of values
which would do credit to a modern designer.
America is fortunate in possessing abundant relics of primitive times
but it cannot be doubted that in other lands similar work was done,
making allowance, of course, for the characteristic variations in
national traits. The potter's craft is of such a nature, using an
omnipresent material and requiring the minimum of tools, that almost
every nation on the globe has practiced it. In some it has never been
developed beyond the narrow limits of the stone age, in others it has
reached the utmost perfection of cultured skill.
For perfection of quality in crude pottery, no ware has ever surpassed
that of Greece. It is not practicable here to deal with the numerous
branches and sub-branches of Greek pottery; let it suffice for the
present purpose to speak of only two main groups. In the first, the
background of the decoration was supplied by the tint of the bare clay;
in the second, this tint afforded the color of the decoration itself,
the background being covered with a black pigment. To speak briefly
these groups are known as black-figured and red-figured wares.
The wheel was early adopted by the Grecian potters as a means of
producing form and although molds were sometimes used, the wheel was, to
all intents and purposes, the sole method of manufacture. Greek pottery
is once fired. Birch classes it as glazed terra cotta, but the glaze is
nothing more than the black pigment with which the decoration is carried
out. The uncolored part of the clay is not glazed but polished with a
hard tool. Probably some famous potters employed assistants either to
make the pieces or to decorate but it does not appear that there was any
reproduction, at least, during the best period. At first primitive ideas
prevailed. Geometric designs were succeeded by rhythmic friezes of
beasts and birds done in black. When the human figure made its
appearance the faces were all in profile with full-fronting eye while
the prominent details of feature and drapery were scratched with a sharp
point before burning.
The change of method to red on black gave much wider scope for the
treatment of the human figure, rendered a fuller expression possible and
enlarged the power of pictorial action. Great skill in drawing was
manifested and details of both drapery and features were expressed with
great care by means of the brush.
Such was the state of the art when the decadence set in and the work
fell into the hands of plagiarists and charlatans. Meretricious coloring
and gaudy ornament succeeded the refinement and restraint of the earlier
days and so the art perished.
To the inventive power of the Romans the ceramic art owes more than one
novelty. It would appear that the desideratum of the early days was a
black ware. Homer in his hymn wrote:
"Pay me my price, potters, and I will sing. Attend, O Pallas, and with
lifted arm protect their ovens, Let all their cups and sacred vessels
blacken well And baked with good success yield them Both fair renown and
profit."
The Greeks accomplished this blackening by means of a pigment, the
Romans secured a similar result by a manipulation of the fire.
It is well known that the oxide of iron which imparts to the clay a red
color will, if burned in what is known as a "reducing" fire, turn black.
This is accomplished by keeping the air supply at the lowest possible
point and the effect is heightened by the smoke which is partly absorbed
by the clay. This black ware is known as Upchurch pottery from the name
of a locality in England where large quantities have been found, but
numerous examples occur in Germany and, indeed, wherever the Roman hosts
encamped.
A second type of pottery is called Castor ware and consists of a dark
clay upon which the decoration is traced in clay of a lighter color. The
decoration was applied as a slip or cream and hence was the forerunner
of the modern slip painting or _pâte-sur-pâte_. This ware is well worth
a study. The decorations consisted largely of conventional borders and
panels but it is specially notable on account of the free use of motives
drawn from daily life. One of the commonest scenes depicted is the hunt
of hare or stag, the animals and trees being often woven into an almost
conventional frieze.
The most valued type of Roman pottery seems to have been the Aretine or
Samian ware. This is a bright red color and possesses an extremely thin
glaze. A particular clay was evidently used, but all knowledge of its
source has been lost.
With the importation of Chinese porcelain by the Dutch the whole trend
of pottery manufacture was changed. No longer was black a desirable
color, white was seen to be much more delicate and beautiful and
henceforth the endeavor of the potter was to produce a ware which should
be as nearly like porcelain as possible. The crudeness of the clay kept
this ideal from being realized, but various expedients were adopted and
gradually better results were obtained.
Throughout the East a type of white pottery was made which, though
stimulated by the Chinese example, may have been a relic of the
knowledge of the Egyptians. A crude clay was coated with a white
preparation, possibly ground quartz, and upon this there were painted
conventional designs in sombre colors. A clear glaze covered the whole
and imparted to the colors a beautiful quality as of pebbles under
water. The nature of the glaze is made evident by the hues assumed by
the metallic oxides employed as colorants. Copper oxide affords a
turquoise blue, manganese, a wine purple, and iron, a brick red. If the
glaze had contained any considerable amount of lead oxide, these colors
would have been quite different; copper would have produced green,
manganese, dark brown, and iron, yellowish brown. The iron pigment was
evidently a clay, sometimes spoken of as Armenian bole. The red color is
always in raised masses because if a thin wash had been used the color
would have yielded to the action of the glaze.
This ware, commonly called Oriental _engobe_ ware, affords a fruitful
study. Effects similar in character were produced by the late Theodore
Deck of Paris, but no considerable use of the ancient methods has ever
been attempted.
The use of tin and lead in glazing was known to the Arabian and Moorish
potters but these ingredients were not abundant in the East. When,
however, the Moorish hosts conquered a part of Spain in the twelfth
century it was found that both lead and tin were available. The result
was the development of the enameled ware known by the generic name
Maiolica. Some have maintained that this was first made in Italy but the
name is derived from the island of Maiorca from which much of the
pottery was exported. The famous Alhambra vase remains as a monument to
the skill of the Hispano-Moresque craftsmen, but it was the Italian
artists of the Renaissance who brought the enameled wares to perfection.
The interest here is artistic and technical rather than historical, but
no one can study the work of the period without learning something of
Luca della Robbia and Giorgio Andreoli, of Gubbio and Pesaro and Castel
Durante.
The use of lead in the glaze proved seductive. It simplified the
technical problems and provided a brilliant surface but alas! the colors
suffered and one by one they succumbed. The blue of cobalt, however,
proved indestructible and so, when the technical knowledge of the South
met the traditions borrowed from the Chinese, there was born, in the
little town of Delft in Holland, the blue enameled ware which has ever
since been known by the name of its native place.
As to the technical details of the production of Delft ware a great deal
of information is available. The clay used contained a goodly proportion
of lime and this served to hold the enamel in perfect union with the
body. The decoration was painted in cobalt blue upon the unburned
surface of the enamel. This was, in a measure, courting a difficulty but
it is the glory of the craft that a difficulty is cheerfully accepted if
in the overcoming there is found success. If the Delft potters had
burned their enamel in order to make the painting easy, the world would
never have enjoyed the tender tone of blue for which this pottery is
famous. By painting the blue color over the powdery enamel, a more
perfect union of enamel and color was accomplished than would have been
possible by any other means. This fact alone is sufficient to account
for the unsatisfactory nature of the modern, so-called, Delft.
Difficulties have been avoided rather than met and the success of the
early masters has eluded their recent followers.
Much of the pottery made in France in the seventeenth century was
inspired by the Italian renaissance. In fact the word faience is due to
the avowed intention of the manufacturers of Nevers to copy the enameled
pottery of Faenza. Almost the only novelty of the time was the
inversion, by the Nevers potters, of the Delft idea. Instead of a white
enamel with a blue decoration they used, in part, a blue ground with a
decoration in white. It is not known that this variation found
acceptance in any other place but in many localities, notably at Rouen,
the manufacture of enameled wares was pursued with great success. The
only real difference between the wares of Spain, Italy and France, lies
in the decorative treatment. Sometimes the emphasis was laid upon
lustres, sometimes on blue and white and again upon polychrome painting.
In one place there was an extensive use made of pictorial treatment, in
another all was conventional. The differences are interesting to a
student or a collector but to the craftsman enameled pottery affords but
one, though by no means an unimportant, means of expression.
France, however, gave birth to two important and interesting departures
from the beaten track; the so-called Henri deux ware, and the faience of
Bernard Palissy. Important as these are to the ceramist, it is a
remarkable fact that neither of them had any appreciable influence upon
the art as a whole nor did they leave any descendants.
A good deal of controversy has raged around the pottery commonly known
as Henri II, some authorities claiming that it should be called Faience
d'Oiron, and others assigning to it the name Saint Porchaire. It was,
quite evidently, the production of an individual or group of individuals
who had no connection with ordinary pottery manufacture, and the small
quantity produced is evidence that it was made for personal pleasure.
The name Henri II is undoubtedly satisfactory, for it was made in the
reign of the second Henry and some pieces bear the monogram of the king.
On the other hand H may be the initial of Helene d'Hengest, who occupied
the chateau d'Oiron and who had in her employ one Bernard who filled the
position of librarian. The style of the work seems to indicate a
devotion to books, for the patterns are suggestive of book-binding tool
work but were not produced in the same way. The ware was made of a
natural cream-colored clay and the shapes were modeled with great skill.
Upon the plain surface patterns were tooled or incised and the hollows
thus formed were filled in with dark-colored clays. The whole was then
covered with a clear lead glaze which afforded a finish very much like
modern earthenware.
The origin of this work is a matter of little more than academic
interest but the technical details are of such importance as to be well
worth a study. The ware is original and unique. No pottery either before
or since has approached it in method, and the quality of most of the
pieces is all that could be desired. Such was the elaboration of detail
that no price could have been set upon the ware and it was evidently not
made for sale. A distinct growth in style can be traced. The first
pieces were somewhat archaic and even crude but as skill was acquired
greater perfection was attained. As is too often the case, however, the
skillful hand overreached itself and the later pieces are loaded with
meretricious detail in many colors. There are only about fifty pieces
known and these are equally divided between the museums of France and
England.
Bernard Palissy was a versatile genius but is here only considered as a
potter. He states in his records that he was inspired by seeing an
enameled cup. It was at one time supposed that this cup was of Italian
maiolica but later authorities incline to the belief that it was a piece
of Chinese porcelain which Palissy supposed to have been enameled. No
white clay was known to him but enameled wares were quite accessible. It
can scarcely be believed that maiolica was a novelty but it can easily
be understood that a piece of white porcelain, viewed in the light of
the contemporary knowledge of enamels, would appear of marvellous
quality.
Palissy essayed to imitate this wonder but attacked the problem from the
standpoint of an opaque glaze. He spent fifteen years in experimenting
but never realized his ideal. He did, however, produce a palette of
marvellous colored enamels. He was a close student of nature and modeled
all kinds of natural objects, glazing them in the proper hues. He also
designed and made vases and service pieces, some with figure
embossments. The story of his struggles is readily accessible to any who
are interested.
Palissy left little or no impression upon the ceramic art of his time
but in recent years some work has been done in colored glazes fusible at
a low temperature. This ware is sometimes sold under the name of
maiolica but it is more nearly an imitation of Palissy. The main
difference between the two types is that while the maiolica or
tin-glazed pottery of Spain, Italy and France consisted for the most
part of a white enameled surface upon which painting was applied,
Palissy used little or no white enamel but decorated his wares with
tinted glazes which themselves supplied the colors.
In the low countries and the German states there was made the striking
and original pottery known as _Grès de Flandres_. The clay was of the
type commonly used for the manufacture of stone-ware and appears in
three colors, brown, gray and cream. The ware was made on the wheel and
embossments more or less elaborate were subsequently added. The unique
feature consisted in the method of applying the glaze. This was simply
common salt, thrown into the heated kiln and volatilized. The salt vapor
bathed the glowing pottery and combined with its substance, thus
producing the delightful orange-skin texture known as salt glaze.
The knowledge of this method was conveyed to England in the seventeenth
century and gained wide acceptance there. The English potters preferred
to use clays which were almost white, and after glazing a decoration in
brilliant colors was sometimes added. Naturalistic treatment was not
attempted but conventionalized subjects were used with almost the effect
of jewelry. The temperature at which this work can be produced varies
with the clay. Many fusible clays will take a salt glaze but the beauty
of the product depends to a large extent upon the purity of the body.
This necessitates a hard fire, for white-burning clays always need a
high temperature for vitrification. The early potteries of England were
dependent largely upon clay effects. Some little enameled ware was made
and is known as English Delft; but the bulk of the work was slip
painted, incised, marbled or embossed. Each of these methods is capable
of an intelligent application and all are within the reach of the artist
potter.
CHAPTER III: PORCELAIN
The production of porcelain is the goal of the potter. The pure white of
the clay and the possibility of unlimited fire treatment exert a
profound influence upon the imagination while the difficulties of
manipulation only serve to stimulate the energy of the enthusiast. For
present purposes not much is to be learned from the soft porcelains of
France nor from the bone china of England. German and French hard
porcelain are but developments of the Chinese idea and therefore need
not be studied apart from their prototype.
The earliest date of Chinese porcelain is unknown. The records of the
nation are very ancient but their meaning is often obscured by the fact
that in the Chinese language the same word was used of old to denote
both porcelain and earthenware. Specimens dating from only the tenth
century A. D. look almost incredibly old. They are coarse and heavy in
structure but are aglow with vibrant color. The finest porcelains date
from the fourteenth and fifteenth centuries and these are the ideals
towards which every modern potter looks.
Broadly it may be stated that two methods prevailed. In the former the
glaze itself was charged with color or the coloring matter was applied
to the clay beneath the glaze. In the latter the porcelain was finished
as to body and glaze and the decoration was applied at a subsequent and
much lighter burn.
The first named class is called single-colored porcelain; the second has
several names such as the famille rose and famille verte as defined by
Jacquemart.
In the single-color class it is evident that the potters were not at all
sure of their results. In many museums there are to be found examples of
ox-blood red, more or less fine, and, with them, other pieces which were
intended to be red but which failed in the fire. The wonder is, in these
cases, that the pieces, even though failures, are beautiful. The
knowledge required for the production of these wares is largely
scientific; at the same time it is not to be believed that the Chinese
had any special scientific training. They evidently traveled a long and
tortuous path before the goal was reached, in fact, they often fell
short of it altogether, but they had plenty of time and unlimited
patience. The modern potter is, if less patient, more fortunate in that
the course has been marked out with more or less accuracy and, if the
landmarks of science be heeded, a certain degree of success may be
attained.
This single-color work is the true field of the ceramist. Anyone
possessing the power of using a pencil, and with a large stock of
patience, may produce over-glaze decoration, but to prepare glazes of
many hues and to consign them unprotected to the fury of the furnace,
requires skill, patience, courage and enthusiasm.
During the last twenty years a new school has arisen which combines in a
measure the advantages of the two Chinese methods. Colors are prepared
from refractory materials and upon clay or soft burned biscuit ware,
scenes, in more or less conventional form, are painted, or else a design
purely conventional in character is applied by the artist. The ware is
then glazed and subjected to the severe fire which all porcelain
undergoes. The result is that the porcelain and the painting are united
in a sense that can never be the case with over-glaze treatment. The
colors become part of a purely ceramic unit; the spirit of the artist is
fixed by the fire.
To this class belong the porcelain of Copenhagen and the recent product
of Sevres. These, of course, represent the result of much arduous
training and many tedious experiments. Both the training and the
experiments are necessary to some extent for every worker, not only
because pottery clays vary much in composition, but because
individuality can only be obtained by the preparation, in the
laboratory, of the desired compounds.
The Chinese, doubtless, stumbled upon many of their successes by
accident, helped by the fact that the character of the fire employed
influenced many of their colors. This will be explained in a later
chapter. They were, however, quick to seize upon that which was good.
Many fanciful names were given to the rarest colors, such as "the violet
of wild apples," "liquid dawn" and "the red of the bean blossom." This
idea has been carried further in France by the invention of such names
as "_Sang-de-boeuf_," "_Sang-de-poulet_," "_clair-de-lune_," etc., and
pursued in this country in "Peach blow."
In the over-glaze treatment, the type named "famille verte" is
characterized by a clear green glaze or enamel over a design in black.
The whole is painted over the porcelain glaze and the green enamel is so
soft that it is often decomposed on the surface. When a broad black mass
is covered with green the decomposition gives rise to prismatic colors
and occasions the term "raven's wing black." Some of this ware has also
been gilt but the gold lines have disappeared and can only be located by
the slight dullness of the enamel where they once were. Well known to
collectors also are the rose-back plates. These belong to the "famille
rose" in which the characteristic note is a delicate rose pink. This
color is prepared from gold and when it is placed upon the back of an
egg-shell plate a tender rosy transparency is imparted to the piece. One
of the best known of the single colors is the pale sea green named
celadon by the French. This color in China was called "the sky after
rain" and was considered both rare and valuable.
The porcelain of Copenhagen is the product of scientific skill and
artistic taste. In the studios attached to the Royal Manufactory there
has grown up a tradition of work and criticism which is fostered by
ladies of birth and position. Many of these paint upon the porcelain
themselves and so constitute a school which has become world famous.
Natural objects are, for the most part, chosen and, as the palette of
colors is, owing to the intense fire, quite limited and low in key, a
tone of quiet atmosphere pervades the painting. This is accentuated by
the use of the air-brush to distribute a ground color upon the ware in
graduated strength.
At the National Manufactory of Sevres there has been some attempt to
follow the Copenhagen method but to a greater extent the work is along
the lines of conventionalized form. In this treatment the French artists
excel, being wonderfully accurate--almost too accurate--in their lines
and spacing. Several individual workers in France have also pursued this
plan, designing and executing the pieces which have made the French
artist-potters famous.
In the porcelains of Berlin the quality lies largely in the complete
mastery of technical details. The work is, as would be expected, German
in style, but the paste is pure and the colors are well prepared.
From this brief review it will be seen that the interest in the
manufacture of porcelain lies not so much in variety as in the value of
individual results. In the pottery described in the previous chapter a
great many different clays were used and each one proved suggestive to
the potter. In porcelain, on the other hand, the body clay is almost
identical wherever prepared, the requirement of a white translucent
paste being paramount.
CHAPTER IV: THE NATURE AND PROPERTIES OF CLAY
Clay differs from earth or soil in that it possesses certain
characteristics which these do not possess. Its distribution is very
wide but for the most part it lies concealed from view. In certain parts
of the country it is so abundant that it breaks through the surface or
is exposed as an outcrop but usually it is covered by the soil which
supports vegetation. Unless the subsoil consists of sand it is easy to
expose a clay by plowing or digging with a spade. It usually appears as
a greenish or bluish substance of close and uniform structure. The
texture is sometimes smooth but more often numerous small stones are
found imbedded in the mass. Such clays as are commonly found can be used
for the manufacture of some kind of pottery but in the great majority of
cases the ware will be red when fired because the clay contains a
proportion of oxide of iron. A pure clay does not contain this and
therefore becomes white or nearly white in the kiln.
Pure clay, known as clay base or clay substance forms a part of all
natural clays though sometimes only a small part. It consists of silica,
alumina and water in a state of combination and is thus known as a
hydrous aluminium silicate. While this substance is very common as an
ingredient of ordinary clay, it is rarely found alone or uncontaminated.
Commercial or workable clays may be said to consist of clay base and
sand, with or without other impurities such as lime and oxide of iron.
For working purposes it may be granted that the potter has to deal with
a mixture of clay and sand. But sand is not a definite expression. It
may vary both physically and chemically within wide limits. The physical
nature has to do with condition, the chemical with composition. Thus a
sand may be almost as coarse as gravel or as fine as the clay itself. It
may be a pure quartz sand or it may be a crushed rock of almost any
composition. The former is known as quartz, the latter as feldspar or
feldspathic sand because it approaches in composition the group of
minerals known as feldspars. Each of these ingredients, clay, quartz and
feldspar, has an important part to play in the transformation of clay
into pottery. Few of the clays used in making white pottery possess
these ingredients in the correct proportions so that it becomes
necessary to make a mixture in which the necessary proportions will be
found.
For successful pottery making three properties are demanded in a clay.
First, plasticity. Without this, clay could not be shaped at all. It
constitutes the obedience of a clay to the forming influence whether
hand or mold. The necessity for this quality may be illustrated by the
proverb "Making ropes of sand" as an example of the impossible. Sand,
possessing no plasticity, cannot be shaped or made to hold together.
The second property is porosity. A clay which exhibits a high degree of
plasticity can be easily shaped but it cannot be safely dried. The water
of plasticity cannot escape and therefore the clay warps and cracks. The
function of porosity is to prevent this. A porous clay permits the water
to escape freely and the clay can be dried without damage. This
condition is produced by the admixture of sand or by the presence of
sand in a natural clay. A coarse sand is more effective than a fine sand
but a sand that is too coarse will interfere with delicate working while
a sand that is too fine approximates the action of the clay itself and
produces a substance which is dense rather than porous. Porosity is
therefore the reverse of plasticity and these two properties must be
adjusted so as to balance each other.
The third necessary property is commonly known as vitrification but
could be better named "densification" because complete vitrification is
not attained in ordinary clay wares. This property may be defined as
that which causes a clay to yield to the action of a high temperature so
that the result is a ware, more or less dense, which is hard, durable
and sonorous. With this there must be coupled a certain amount of
resistance to heat treatment so that the pottery does not fuse or
collapse during the firing. Here also is found the need for adjustment.
The clay must yield to the fire but not completely. It must resist but
not entirely.
Plasticity is due to the clay base. Not only to its quantity but to its
quality also. Some forms of clay in which clay base predominates are not
plastic because the clay base itself is coarse grained. Other forms with
less clay base present are plastic because this ingredient is fine
grained and tough. Pure clay base is also highly resistant to fire and
therefore contributes to the refractoriness of the mass.
Porosity is caused by the sand in the clay. Any kind of sand will
produce porosity but the effect differs with the condition of the sand.
Coarse sand is more effective than fine sand. More sand will, of course,
cause greater porosity.
Vitrification or densification is due to the feldspar or fusible sand.
This also varies with the condition. A fine-grained feldspar will
produce vitrification more easily than the same amount of coarse
feldspar.
Certain substances are available for use in pottery mixtures, which
possess one or other of the necessary properties in high degree so that
they will impart these properties to a mass to which they are added.
Kaolin or china clay is usually fine, white, and refractory. Some
kaolins are rather plastic but most of them are "short" in working and
rather tender. For the production of a white ware kaolin is
indispensable. No other ingredient will afford the pure white color
which is sought after in porcelain and china.
Ball clay is very plastic, easily vitrified, but is not white. The color
varies from a cream to a gray. The use of a ball clay is therefore
limited in white wares because it will spoil the color. For wares in
which a light cream color is not objectionable ball clays are valuable
and almost indispensable.
Stoneware clay is usually a rather plastic clay which contains a good
deal of sand, hence stoneware clays can be used for certain classes of
ware without admixture. A rather high temperature is required for most
of these clays, though occasionally one can be found which will become
dense at the fire of a studio kiln. The clays sold by the Enfield
Pottery Company and by the Western Stoneware Company are of this type.
Ground flint is a necessary ingredient in almost all pottery. It aids in
the porosity of the clay and enables the mixture to be adjusted to fit a
special glaze.
Ground feldspar is also necessary. Like flint it aids in the porosity of
the unburned clay but unlike flint it produces density in the firing.
By a proper adjustment of these ingredients a clay can be composed which
will meet the special requirements of the worker.
In order to ascertain the properties of any given clay certain simple
tests may be made and every clay-worker should know how to do this
because one cannot be too well informed as to the materials to be used.
First, water of plasticity. A certain portion of the clay, dried and
powdered, is weighed out. It is convenient to weigh in grams and to
measure in cubic centimeters because in this way calculation is easy.
The scales and weights are described in the chapter on glazes. For
measuring the water a glass vessel called a graduate is used. One
holding a hundred cubic centimeters and graduated in centimeters and
tenths can be obtained from a dealer in chemical supplies. One hundred
grams of clay is weighed out and transferred to a glass slab. The
graduate is filled with water to the one hundred mark. Some of this
water is then poured on to the clay, adding little by little as needed
until the whole can be worked into a stiff mass of the proper
plasticity. The quantity of water used is then carefully noted by
observing how much is left in the graduate. Suppose, for instance, 70
cubic centimeters are found remaining, the hundred grams of clay has
absorbed thirty c.c. of water and as one c.c. of water weighs one gram
the clay has taken just 30 per cent. This amount is important because it
is one of the best indications of plasticity. A very plastic clay may
need 40 per cent, a non-plastic clay may be satisfied with 25 per cent.
Second, shrinkage. The mass of plastic clay is now transferred to a
plaster bat and rolled or pressed out into a smooth slab about 12
centimeters long. Here again the centimeter is used in preference to the
inch as being more easily calculated. A faint line is ruled on the clay
slab and two fine scratches are marked exactly ten centimeters apart.
The edges are trimmed and the excess clay made up into three or four
small pieces which are to be fired in different parts of the kiln as
tests for density. When the clay slab is dry the distance between the
marks is measured and noted. The ten centimeters being divided into one
hundred millimeters, each millimeter of shrinkage means one per cent.
After firing, a second measurement is made and the differences are noted
as dry shrinkage and fire shrinkage respectively.
Third, firing. The slab with the measurement upon it is set in the kiln
in the place where the clay wares are to receive the first or biscuit
fire and the small pieces are arranged in different places so as to
secure as many different conditions as possible. The position of each
should be carefully recorded. After firing, the marks on the slab are
measured as already described and note is taken of any warping of the
piece. The color is also recorded. The small pieces should be tested for
porosity or absorption of water but this is rather a delicate operation
and needs a particularly sensitive balance. Generally it will suffice to
use a wet sponge or to dip each piece into water, removing it quickly
and noting carefully the rate of speed at which the water is absorbed.
If the water should be scarcely absorbed at all a line of ink may be
drawn upon the pottery with a pen, the piece being perfectly dry. In a
fully vitrified ware the ink can be washed off, leaving scarcely a mark
but the test is quite sensitive and with a little practice will afford
an excellent means of comparing the density of different clays or of the
same clay at different temperatures.
Fourth, glazing. It is well to have ready a small supply of a standard
clear glaze. Each of the test pieces should be covered with this in a
rather thin coat and then they should all be fired again, this time
close together so that they will receive the same heat treatment. This
will enable one to determine what degree of fire for the clay will best
suit the glaze.
CHAPTER V: THE PREPARATION OF THE CLAY
A clay having been selected in accordance with the tests described, it
becomes necessary to prepare it for use. A fairly large supply should be
obtained and stored in a dry place. Most natural clays need some kind of
cleansing for there are almost always foreign substances present. This
cleansing is accomplished by reducing the clay to the fluid known as
slip. The necessary appliances for making slip are as follows:
A large sieve of quarter-inch mesh.
A small wire sieve of about 14 meshes to the inch.
A large barrel.
Two galvanized pails.
The clay is, after drying, powdered and sifted through the large sieve.
One of the pails is half filled with clean water and the clay, handful
by handful, is sprinkled into it. The clay rapidly absorbs the water and
sinks to the bottom. The addition of clay is continued until a small
mound rises through the water, when the whole is left to soak for an
hour. The bared arm is then plunged into the pail and the mass stirred
vigorously. A stick or paddle will serve, of course, but the potter
learns a great deal by the feel of the clay and therefore the hand is
best. It is said that he is a poor sailor who will not dip his hands in
the tar bucket and in like manner, he is a poor potter who fears the
slip tub. This stirring will tell a good deal about the probable working
of the clay. It may be stony or sandy or greasy. The large stones and
roots will have been removed by the sieve but now, after thorough
mixing, the slip is poured through the small sieve into the barrel. Both
pails may be kept going at once, one being filled while the other is
soaking and so on until the barrel is full or, at least, a good quantity
of slip has been prepared.
If the clay prove very sandy it should be washed. The mixture in the
pail having been well stirred is allowed to stand for a definite time,
say one minute. The slip is then poured into the second pail and it will
be found that a quantity of sand has settled. This is thrown away and
the slip in the second pail is examined. If enough sand has been
removed, the slip may be poured into the barrel, using the fine sieve as
already described. If still sandy the process should be repeated, the
settling being for two minutes. Experience is the best guide in this
operation but all the sand should not be removed.
When the barrel is full of slip it is allowed to stand over night when
some inches of clear water will be found at the top. This is removed
with a siphon which may be made of a piece of lead or rubber pipe. The
removal of the water results in the thickening of the slip and the
contents of the barrel should be thoroughly stirred with a long wooden
paddle to insure a uniform consistency. If the slip is found to be still
thin another settling and removal of the water will thicken it.
The slip thus prepared will keep indefinitely, provided that it is not
allowed to become dry by evaporation. It improves greatly with age. This
is the material which is used for casting as will be described later but
for plastic work it must be still further thickened. A shallow box may
be procured and made water-tight and the slip, when poured into it, will
thicken much more rapidly than in the barrel, but it is better to have
some shallow plaster dishes as the plaster itself absorbs the water and
thickens the clay. Instructions for making these dishes appear in the
chapter on plaster.
These directions will suffice for the preparation of a natural clay but
it is sometimes desired to prepare a white body either of earthenware or
porcelain. These bodies do not exist in nature and therefore a mixture
must be made. The ingredients are kaolin or white porcelain clay, ball
clay or plastic potters' clay, ground quartz or flint, and ground
feldspar.[B]
[B] Georgia Kaolin and Tennessee Ball Clay may be procured from the
John H. Sant and Sons Company, East Liverpool, Ohio, and flint and
feldspar from the Golding Sons' Company, Trenton, N. J., or the
Eureka Flint and Spar Company, Trenton, N. J., in quantities of not
less than one barrel or sack.
A suitable mixture for earthenware is--
Georgia Clay[C] 20 parts by weight
Tennessee Ball Clay 30 " " "
Flint 35 " " "
Feldspar 15 " " "
---
100
and for porcelain--
Georgia Clay 45 parts by weight
Flint 35 " " "
Feldspar 20 " " "
---
100
[C] If English china clay can be procured it will make a whiter ware
than Georgia clay.
The earthenware will be creamy in color and porous at an ordinary fire.
The porcelain will need a hard fire and will be white and translucent.
It is, however, non-plastic and hard to work. The preparation of these
mixtures of course necessitates a pair of scales but otherwise the
treatment of the mix is the same as that of natural clay. Washing is not
necessary but the clay must be powdered, mixed with the flint and spar,
and sprinkled into water as already described. In place of the wire
sieve, however, a silk lawn of 120 meshes to the inch should be used.
The lawn is simply a fine sieve and is named because of the material
(also called bolting cloth), with which it is covered. Have a carpenter
make a box without a bottom. Cypress or oak should be used and this
should be a full half inch thick. Four strips of the same thickness are
also to be provided. The box may be of any convenient size; eight inches
square and four inches deep is about right. The sides should be fastened
together with brass screws to avoid rust and a piece of lawn is strained
tightly across the bottom and secured with copper or brass tacks. A
strip of coarse muslin folded and laid along the edges will help to
prevent the lawn from tearing, the tacks being, of course, driven
through both muslin and lawn. Then the four wooden strips are set upon
the muslin and secured with brass screws. The completed lawn is then a
tray of which the bottom is formed of lawn. The strips of wood beneath
serve to protect the lawn when placed on a table as well as to assist in
holding it firmly.[D]
[D] Silk lawn of any desired mesh may be purchased by the yard from A.
Sartorius & Company, 57 Murray Street, New York City; or brass
sieves ready for use from the W. S. Tyler Company, Cleveland, O.
For storing clay in the plastic state there is nothing better than
stoneware jars. These may be had of any size and a tinman should make
close-fitting covers. Earthenware covers do not fit tight and are always
getting broken. A little water is poured into each jar and a support
provided for the clay so that it does not rest in contact with the
water. Under any conditions clay will slowly harden so that not too
large a stock should be kept. Slip, on the other hand, keeps well so
long as some water is always on the top and it is not a long process to
stiffen it into clay.
CHAPTER VI: MOLD-MAKING AND PLASTER
Plaster is almost a necessity to the potter and therefore something
should be learned about it. Even if one does not use molds there are
numberless purposes for which plaster is convenient. For stiffening slip
into clay, and for absorbing water from glazes, shallow dishes of
plaster are used, and for holding work either in making or drying,
plaster bats or round slabs are always in demand.
It is best to purchase the finest quality of potters' plaster by the
barrel.[E] It will keep indefinitely if stored in a dry place. The
necessary appliances are:
One or two large jugs for mixing, or a metal can with a spout.
A metal spider or frying pan.
Six feet of rubber machine belting, six inches wide, or similar strips
cut from linoleum or enameled cloth.
Two or three thin pieces of steel of various degrees of flexibility
(scrapers).
Handy knives, called vegetable knives.
A small painter's brush.
Two or three fine sponges.
[E] Calvin Tomkins, 30 Church Street, New York City.
To begin with, a size of soft soap and water is prepared. Put a quart of
water into a kettle and add a piece of soap the size of an egg.[F]
Simmer for an hour or until the soap is entirely dissolved and then set
aside to cool. When cold the size should be of the consistency of maple
syrup. This size is used whenever plaster is to be kept from sticking to
a form or surface, and it has also the merit of causing clay to stick to
plaster. For example, if a mold is to be taken from a clay model no size
should be used, but if a plaster form is used as a foundation for clay
ornament it should be well sized first. The size is laid on with a brush
and wiped off with a sponge. Another sponge is then used with clean
water and the sized surface is washed, all superfluous water being
removed. Size is then applied a second time and washed off as before. A
third application is sometimes necessary, or until the sized surface
rejects water like grease does. On the last sizing, water is not
applied, but the surface is polished with the sponge containing size. If
the surface to be prepared be of wood or metal a single coat of size
will often suffice, but if it be of plaster three or four applications
are often necessary.
[F] Any good laundry soap will serve, but it should be sliced thin.
The first lesson may well be the manufacture of a plaster bat. The
frying pan is first sized and set upon a level table. Let us suppose
that a quart of water will fill it to about an inch in depth. This
amount of water is put into a jug and two pounds and three-quarters of
dry plaster is weighed out and allowed to trickle through the fingers
into the water. This proportion has been found to be best for ordinary
mixings. A smaller quantity of plaster to the quart of water will result
in a very soft bat; a larger quantity will be proportionately harder.
After the plaster has soaked up all the water it will take, that is in
about two minutes' time, the hand is plunged in and the whole stirred to
a smooth cream. All lumps must be broken up and the air bubbles removed
as far as possible. Continue stirring gently and presently the mixture
will be felt to grow thicker. The psychological moment arrives when the
plaster forms upon the hand a white coating which cannot be shaken off.
The creamy liquid is then poured into the frying pan which is gently
shaken to level the surface.
If the plaster has been poured at the right moment it will set smoothly
with a mat surface like sugar icing. If poured too late it will be stiff
and difficult to level, and if poured too soon it will curdle on the
surface and water will be seen above the plaster. A little practice will
show the right moment. The jug should be washed out immediately while
the plaster is soft. In the place used for plaster work a tub should be
provided in which all vessels and tools can be washed, for, if allowed
to flow down the waste pipe of a sink, the plaster will speedily choke
the outflow.
After standing for some ten minutes, more or less, the bat in the frying
pan will grow warm. This is the sign of a combination between the
plaster and the water and shows the completion of the setting. The pan
is now taken by the handle and, holding it upside down, the edge is
rapped smartly on a brick or stone. This will cause the contents to fall
out and there is a smooth disc which is one of the most useful of
appliances. The edge will need to be scraped and the bat can be set
aside until needed. It will be good practice to make a half dozen of
these.
This process of mixing and pouring plaster is the same for all
operations and the instructions will not be repeated, but when the
student is told to "pour plaster" it will be presumed that this
experiment has already been made.
[Illustration: Fig. 1. _A_, table. _B_, clay mound. _C_, plaster. _D_,
rubber belt.]
The next step is the making of a plaster bowl or dish for the purpose of
drying out slip or glaze. A convenient size should be determined upon as
it is best to have all the dishes the same. Upon any flat, smooth
surface a mound of clay is reared which shall be the size and depth of
the inside of the proposed dish. About twelve inches in diameter and
three inches deep is a good size, though fourteen inches is not too
large for the former dimension. This mound should be made as nearly
circular as possible and the clay finished as smoothly as may be. The
rubber belt is then set around the mound in the form of a hoop leaving a
space of two inches between the clay mound and the rubber hoop. The
rubber is fastened either by tying with string or by binding the
overlapping ends with clothes pins. A roll of soft clay is laid down
where the belt joins the table and pressed down outside to prevent
leakage. Enough plaster to fill the space within the belt is now mixed
and poured, covering the clay mound to a depth of at least one inch.
When the plaster has set the rubber is detached, the whole turned over
and the clay dug out. We have now a circular plaster dish three inches
deep but we have only one. The trouble of rebuilding the clay is
unnecessary a second time because a "case" or reverse can be made from
which as many dishes as may be necessary can be formed.
[Illustration: Fig. 2. _C_, plaster dish. _D_, rubber belt. _E_, plaster
case or reverse.]
[Illustration: Fig. 3. Plaster case, with rubber belt, arranged for
pouring.]
The dish is carefully smoothed and trimmed. The sharp edge is removed
and the inside is dressed with fine sandpaper to a perfectly smooth
surface. Size is now applied to the inside and upper edge until a bright
slippery surface is obtained. The rubber belt is now bound closely
around the dish and plaster is poured to a depth of about one and
one-half inches on the edge. This, of course, makes a depth of four and
one-half inches in the center. When this new plaster has set in turn the
rubber is removed and the two castings can be easily separated by
inserting a knife at the junction. The knife should be gently driven in
with a hammer. Obviously it is now possible to make a number of dishes
from the reverse thus obtained, by simply binding the rubber belt around
each time and pouring plaster as at first. The original mold having been
sized is no longer absorbent but must be kept in case additional
reverses are needed. The molds or dishes must be thoroughly dried out
before being used.
The molding of a vase form is more elaborate but not really difficult.
Even if one does not intend to produce pottery by molding there is
always an advantage in having a number of simple forms upon which to
make experiments.
The vase to be molded is first drawn to exact size upon paper and a
plaster model is turned on a lathe. This can be done equally well on the
potters' wheel and the method is as follows: A plaster bat is saturated
with water and set upon the wheel so as to run true when the wheel is
revolved, and is cemented to the wheel head by a little slip. A few deep
scratches are made on the face of the bat and a cylinder, either of the
rubber belt or of stiff paper, is rolled up and set on end in the center
of the bat. The size of the cylinder should be a little larger every way
than the proposed vase. Plaster is now mixed and poured to fill the
cylinder. It will adhere to the bat below by reason of the scratches.
When the plaster has set, the cylinder is unfastened and removed and the
turning may begin. To turn plaster well involves a good deal of practice
but it is better to spoil three or four plaster cores in the learning
than to spend a long time on one for fear of damaging it.
[Illustration: Fig. 4. Turning tools for plaster.]
[Illustration: Fig. 5. Position of tool in turning. _A_, correct. _B_
and _C_, incorrect.]
The board support and turning stick described on page 100 are used in
turning plaster as well as clay. The turning stick is held in the left
hand and the point is pressed into the board. All this is, of course,
made ready before the plaster is poured. The turning tools are here
illustrated. They are not sold in the stores but can be made by any
machinist. The head or cutting blade consists of a flat piece of steel
through the center of which is a shaft or pin which is driven into a
handle. The head may be of any shape but the triangle and the circle
will meet every need. The tool is held in right hand and braced against
the turning stick, the stick and tool being moved together by raising or
lowering the left hand which holds the butt of the stick.
While the plaster is still soft the round tool is used and the rough
form is rapidly turned. Then as the setting of the plaster proceeds and
it is found to grow harder, the triangle tool should be used and the
shape gradually wrought out with the point. Finally by using the circle
tool for concave lines and an edge of the triangle tool for convex lines
the form is perfected. The surface is to be finished and the tool marks
removed by using, free hand, a flexible scraper which is bent by the
fingers and thumb to fit the lines of the form, and a final smoothing is
given by fine sandpaper, the wheel being revolved all the time. At the
top of the form a small cylindrical piece is left, called the "spare"
which represents the thickness of the mold substance, and for the bottom
a small piece is turned in the shape of a truncated cone. The small end
of this should be the same diameter as the base of the vase. These are
shown in the illustration (Fig. 6).
[Illustration: Fig. 6. Vase with foot piece and template. _A_, vase.
_B_, spare. _C_, foot piece. _D D_, templates. _N N N N_, natches.]
It will be obvious that in the directions given above the base of the
vase is not finished off and therefore the form must be cut off from the
bat, either by a knife or saw, and the base is then finished by hand, or
by setting the form upside down in a clay cradle--called a "chum"--and
turning the base true. The form is now ready for molding.
[Illustration: Fig. 7. End plates for mold. _E_, upper plate. _E'_,
lower plate. _N N_, natches.]
The plaster vase is laid upon its side on a piece of soft clay and a
thin bat or plaster slab is cut to fit the outline. This template should
fit with reasonable accuracy but need not be absolutely exact. A pair of
these will be required, one to fit each side of the form. These slabs or
sheets of plaster are always useful and if a sheet of glass is kept
handy any excess of plaster left from a mixing may be poured on to it.
This upon setting is easily detached and will present a smooth face
where it has rested on the glass. The pair of templates must include, in
their outline, both the spare and the foot piece but should not extend
beyond either of these. The outside diameter of the mold is now to be
determined and the templates cut to this dimension so that the two
together, with the vase between them, constitute a longitudinal section
of the mold.
The vase must now be divided accurately into two halves by a line
running from top to bottom. There are several ways of doing this. While
the form is still on the bat a diameter of the bat may be drawn and a
perpendicular erected from each end of this diameter. These
perpendicular lines will, of course, mark the center of the vase on each
side; or after the vase has been cut off another method is possible.
With a pair of dividers find the center of both the top and the bottom
of the vase. Mark each with a small hole or the point of a pencil. Now
lay the vase on its side on the clay cradle upon a glass sheet or other
level surface and raise or depress one end until the two centers are
exactly the same height from the glass. Take this height in the dividers
and, sliding one of the compass legs along the glass, gently scratch the
plaster vase with the other or upper point. If the two centers have been
accurately adjusted this scratch line will be the exact center of the
form.
Some soft clay is now built up on each side of the vase and the
templates are pressed down upon it, one on each side until the upper
face of each corresponds with the scratched line. The vase is now seen
to be buried as to one half in a plaster surface, and plaster poured on
this will give a half mold. There is yet, however, nothing to confine
the plaster and it would flow away as fast as poured. Two end plates are
necessary and these must rise in a half circle above the bed formed by
the templates. The part below may be of any shape but must be high
enough to cause the diameter of the half circle to coincide with the
plane of the templates. Two pieces of cardboard, wood, or rubber belt
are now bound to the sides, the apertures at the top and bottom, caused
by the curve of the end plates, are stopped with clay and the whole
presents the appearance of a vase, only half of which is visible, lying
in a shallow trough. All the fitting should be carefully done but the
tying up is not yet. The whole is now taken apart and well sized. Vase,
foot piece, templates and end pieces are all to be sized thoroughly in
the manner described. They are then put together again and bound around
with twine. It is necessary now to make provision for the proper fitting
of the halves of the mold. This is done by providing knobs and hollows
which fit together. These are technically known as "natches" and will be
referred to as such. Take two pieces of moderately stiff clay each about
the size of a cherry. Roll them into neat balls and cut them in two with
a thin knife. Lay each of the halves, flat side down, upon the
templates, two on each, placing them in pairs opposite to each other.
Affix two or more of these on the inner face of the bottom end plate.
Now mix and pour the plaster. This should be poured to the height of the
top of the end plates and, after pouring, shake this well down by
dipping the fingers into it, so that no bubbles may cling to the
surfaces below. As soon as the plaster has become firm but while it is
still soft remove the string and the side boards, pull off the pieces of
clay and with a straight, thin piece of wood scrape off the surplus of
plaster by following the line of the end plates and thus making a half
cylinder.
As soon as the plaster has become warm the whole may be turned over and
the templates and end plates removed. The four half spheres of clay will
be found embedded in the face of the plaster and these, being removed,
will leave four hemispherical depressions. The vase can now be gently
detached from its bed and the first half of the mold is completed. A
little dressing will be necessary. All overhanging edges and rough
places should be finished off and the hollow natches smoothed with a
piece of muslin on the end of a finger.
The second half is simple. Replace the vase in the half mold, set the
foot piece in its place, replace the end plates with the diameter on the
line as before but with the semi-circular edges upward, and set two or
three clay natches on the bottom one. Size, bind up, pour and scrape off
as before, thus completing the two halves of the mold in cylindrical
form. It only now remains to make the bottom for, at present, the mold
is open at both ends.
The two halves with the vase inside are bound very tightly together with
twine and set on the table bottom upwards. The clay natches in the
bottom are taken out and the hollows smoothed. The foot piece is taken
out and the rough places dressed. The bottom end of the vase is now
visible and this, together with the end of the mold, is sized. A strip
of stout paper is bound around the mold, projecting about an inch above
the end and plaster is poured to fill it. When this is set the paper is
peeled off and the edges of the mold are dressed smooth. The bottom may
now be detached by inserting a thin knife at the junction, the mold
opened and the form taken out. The mold is now in three parts which may
be put together at will and used for casting the vase in clay.
CHAPTER VII: CASES AND WORKING MOLDS
The mold described in the previous chapter is called, technically, a
"block mold" and is not, as a rule, used for making the clay ware. The
reason for this is that molds will wear out more or less rapidly and to
repeat the process of making new ones from the original form would be
tedious and expensive.
From the block mold a reverse is made, called a "case," and from this,
in turn, working molds are made in any required number. While it is
possible to use the block mold as a working mold, and, if only a few
pieces are required this is quite sufficient, yet, as it is often
necessary to have a number of molds, the student should understand how
to make a case.
A case may be defined as a mold from which a mold is made. If one can
imagine the visible half of the vase form as it appears in making the
mold, with the templates and ends cemented into one piece, one has a
conception of one half of a case. The problem is to make this with
permanent but movable ends so as to have a convenient form from which
half molds may be easily made.
[Illustration: Fig. 8. Offset plates. _F_, top plate, front view. _F'_,
side view. _G G'_, bottom plate.]
[Illustration: Fig. 9. Sectional view of mold ready for casing. _A_,
mold. _B B_, offset plates. _C C_, end plates. _N N_, natches.]
The ends are joined to the body by means of offsets and the first step
is the construction of these. One half of the block is taken and laid
upon its back, being supported by clay so that the face is level and
steady. An offset plate is now cut to fit each end. To make these a
piece of plaster is selected or made which is true and smooth on both
sides. The plates are cut of the same width as the mold and are beveled
at the upper edge so as to rise slightly from the mold face. The curve
at the end of the mold is cut out to fit and beveled in like manner.
Then two end plates are fitted. These should be about two inches higher
than the offset plates and are square at the top. Upon each of these two
or three clay natches are set, being placed low down near the face of
the mold. The mold and plates are well sized and bound together with
side walls just as in the making of the mold. Plaster is poured to a
height sufficient to well cover the natches and left to set hard. No
shaping is necessary. When well set the end plates and offset plates are
removed but the vase mold and the case are left attached together. The
other half of the mold is prepared and run in the same way, the same
offset plates and end plates being used with such slight refitting as
may be necessary. The work is now examined and all rough places and
scraps of adhering plaster are removed. The two halves of the case, the
half molds being still attached, are set up on end, back to back, being
separated by a thin piece of plaster or a strip of cardboard which
should extend two inches above the top. The top ends are now sized, the
natch holes having been smoothed off, a band of paper is tied around and
plaster poured on top to a depth of about one inch. When set the whole
is turned over and the operation is repeated on the other end. After the
final setting the ends are easily removed and by the insertion of a thin
knife driven by a light blow, the molds and case are separated. Each
half case is now laid on its back and the proper ends are fitted in
place. It only now needs the usual side walls to be tied on and molds
can be made with ease just as the original block mold was made.
[Illustration: Fig. 10. Mold and case in position. The top ends are
lifted to show fitting. The bottom ends are not shown.]
It now remains to make a case of the bottom mold. The bottom piece of
the block mold is taken and sized and with a strip of paper bound around
it, plaster is poured. The two are detached when set and the case is
finished. It consists of seven pieces; three are used in each half and
one for the bottom.
[Illustration: Fig. 11. Block of plaster with face of plate turned. _B_,
height of plaster to be poured. _C_, rubber belt.]
Thus equipped it is possible to make any number of working molds and if
the case should wear out or be damaged, a new one can always be made
from the block mold. The block mold itself, having been sized, is no
longer absorbent and cannot be used for making vases. The working molds
should be thoroughly dried before using and they will last longer.
Flat ware, such as plates and saucers, is made on, not in, a mold. The
diameter of the plate having been decided upon, a block of plaster three
inches wider is run. This is placed on the center of the wheel or jigger
and in it the face of the plate is turned. This must be sunk below the
level of the block and when finished, must appear as though the plate
itself were embedded in the plaster. One half of the thickness of the
edge is shown in such a way that there is no under cutting. Just outside
of this edge the plaster is turned so as to slope gently up to the level
of the block.
Without removing the block from the wheel the face of the plate is well
sized, a band of belting is arranged, of the same diameter as the edge
of the slope and plaster is poured to a depth of three inches. Out of
this the back of the mold is turned as shown in the illustration (Fig.
12).
[Illustration: Fig. 12. _A_, block of plaster. _B_, mold poured on face
of plate and turned.]
The top of this as it lies upside down is shaped with a straight, almost
upright slope which enables the mold to be set securely in the wheel
head. Around the exposed edge of the original block, three or four
natches are now bored or cut. They should be placed at irregular
distances so that there will be no doubt as to the putting together of
the sides of the case. If two circular pieces of plaster have to be set
together and held by natches there should always be either this
irregular spacing or some distinctive mark, because if this be not
provided for, two or three trials will always be made before the correct
fitting is found and these trials wear out the natches very quickly.
[Illustration: Fig. 13. _A_, bottom of case. _B_, Cavity for pouring
molds. _C_, top of case.]
The back of the plate mold and the edges of the block are now sized and
plaster is run to the level of the highest part of the mold but no
higher (Fig. 13). When this is set, the two halves of the case can be
separated and the mold taken out. Now when the halves of the case are
fitted together there will be a cavity the exact size of the mold. This
can be filled again and again with plaster, a new mold being formed each
time.
[Illustration: Fig. 14. Iron prong to fit wheel head.]
[Illustration: Fig. 15. _A_, plaster, with prong inserted. _B_, rubber
belt.]
In order to use these molds a special head must be provided for the
wheel. The regular head of the wheel should be detachable and in its
place an iron frame called a prong is fitted. This consists of a collar
either with a hollow cone or a screw to fit the shaft of the wheel, and
from this radiate four short arms. In order to use this a circular block
of plaster some two or three inches thick is poured on a table or slab
and just as this is setting, the prong, upside down, is pressed into it
just below the surface and held there until the plaster is hard enough
to support the weight of the iron. When hard, the whole is lifted and
the prong with the plaster attached is set in position on the wheel.
This now forms a rough plaster head and it must be turned true. In this
head a circular depression is to be turned which will exactly fit the
back of the plate molds. If the recess should wear larger as it will if
much used, a new head can easily be run. The same principle can be
applied to the making of molds for saucers.
[Illustration: Fig. 16. Wheel head with plate mold. The tool used is
shown in dotted outline.]
Cups and bowls are molded from the outside. A block of plaster about one
inch thicker than the height of the proposed cup is taken and centered
upon the wheel. Out of this the piece is to be turned, upside down,
leaving a ledge or platform, the outside diameter of which is the size
of the mold. The rubber belt is tied around this and the mold poured. If
for casting this will suffice, but if it is intended to make the cups
upon the wheel the outside of the mold must be turned to fit a
wheel-head which is hollowed to receive it. The making of the cups is
described in Chapter XI. A bowl is simply an enlarged cup.
CHAPTER VIII: BUILDING BY HAND
The production of pottery by hand is a form of modeling but with the
important difference that while pieces modeled by art-school methods are
not intended to be preserved in the clay itself, built pieces are
destined for the fire. It is therefore necessary not only that a special
clay be used but that the work be such as will hold under the strain of
the burn. The composition of the clay has been dealt with in another
chapter and it is presumed that the worker has decided upon the proper
mix or has procured a suitable clay.
There are two possible treatments of built pottery; the work may be
finished by fingers and tools only or it may be placed upon the wheel
and turned to a true surface. In the latter case the result is much the
same as if the piece were thrown on the wheel as will be described. The
principal point of difference is that while building needs less practice
than throwing, turning a built piece is much more difficult and tedious
than turning a thrown one. It is almost impossible to build with
sufficient accuracy for the work to run true, and a great deal of time
is consumed in filling hollows and removing lumps. These do not appear
obtrusive when the work is held in the hand, but if it be revolved upon
a fixed center every slight irregularity appears to be accentuated. On
the other hand the charm of built ware lies in the subtle plastic
quality which belongs to no other material or method.
For very large pieces such as tree pots the combination method is useful
but these should be built on the wheel itself and kept true as the work
proceeds. Then a slight turning at the finish, when the clay is leather
hard, will produce a satisfactory result.
The clay for building should be rather soft as it is apt to dry quickly
on handling. The work may be done either with coils or pieces.
A plaster bat should be made with a low dome in the center. This bat may
either fit the wheel or not, depending upon the plan adopted. The dome
is to raise up the bottom of the vase and form a foot. The table may be
covered with a piece of oil cloth or may be kept slightly damp. The
first attempt should be to build a cylinder as this form is easy to
construct and to keep true, so that the attention may be devoted to the
manipulation of the clay.
It is first necessary to roll out the clay into cords which should be a
little thicker than the proposed walls are to be. These cords should be
as uniform as possible and should be rolled quickly to avoid undue
hardening. It is best to roll them as required. The domed bat is made
quite damp and upon it should be marked the diameter of the cylinder to
be built. A roll of clay is taken, one end laid in the center of the bat
and the rest is coiled around it in a spiral line. When the disc so
formed has reached the proper size, the coils are gently rubbed over
with the fingers until they have thoroughly united and the lines of the
spiral have disappeared. The clay disc may now be turned over and the
rubbing continued on the other side. The circle is cut true and a new
coil is laid on the outer edge thus making a shallow circular tray. In
raising the walls it is best to pinch off the roll of clay when one
circle has been completed and the new roll should be begun at another
point so that all the joints will not be at the same place. This plan is
better than coiling a long roll in a spiral for in this case one side of
the piece will be higher than the other.
After three rolls have been laid in position the wall, both inside and
out, should be worked like the bottom so that the rolls will disappear
and the clay be welded uniformly together. This should be done without
water or with as little as possible. The use of water is very tempting.
It makes the clay so smooth and seems to help but it will inevitably
make the work sloppy and will tend to soften the walls.
After three or four rolls have been worked in, the piece should be laid
aside for some hours to stiffen. If this be not done the weight of the
second building will cause the work to sag and fall out of shape. For
this reason it is well to have two or three pieces in hand at once so
that there need be no waiting. When the cylinder is of sufficient height
it should be allowed to become quite stiff and then the irregularities
should be corrected with a little soft clay which is worked into the
joints. The whole surface may now be gone over with tools and brought to
the required finish. As soon as the clay is hard enough it should be
removed from the damp bat and placed upon a dry one to become dry.
In the method of building by pieces no rolls are prepared but the clay
is taken, pinch by pinch, each morsel being pressed into place as the
work goes on. This plan is somewhat more plastic in effect and is well
adapted to free-hand work; the resulting pottery, however, is generally
thicker and heavier.
The craft of building is not mastered until the lines of a drawing can
be successfully followed. The clay is apt to choose its own way and the
result will be very different from what the potter intended. The design
should be carefully worked out on paper, full size if possible, and the
clay form should be compared with the drawing as the building goes on. A
profile may be cut in cardboard and this, applied to the clay from time
to time, will verify the line, but all such mechanical aids should be
used sparingly as the value of this work depends largely upon the sense
of freedom and self-expression which belongs to it.
The thickness of the clay walls is a matter of great importance. A small
piece should not be so thick as to feel clumsy and heavy, nor should a
large piece be so thin as to lose the sense of strength and solidity.
It may be found on drying the ware, that cracks, especially in the
bottom, are developed. The cause of this may be in the clay. A clay
which is too plastic or too fine in the grain will surely crack. Such a
clay may be opened or meagered by the addition of ground flint or fine
grog. The cause may, on the other hand, be in the building. If the
welding of the coils or pieces be imperfectly done, cracks are sure to
result. If the bottom be too thick it will crack. A great strain is put
upon the bottom in drying. The clay must be able to shrink and while the
side walls are able to settle down on themselves, the bottom is pulled
in every direction by the sides. The bottom should be made quite thin in
the center and thicker toward the edges. This will help to avoid cracks.
A bad crack cannot be successfully mended. It is best to break the piece
and begin again. To burn it means the loss of the clay but the clay will
be saved if the damaged work be withheld from the kiln. A small crack on
the edge is also hopeless. A crack showing on the edge of a piece is a
bad fault. A small crack in the bottom may be mended by dampening the
place carefully and pressing in a little stiff clay.
CHAPTER IX: THE POTTER'S WHEEL
Much of the glamour of the potter's art is associated with the wheel.
Poets have sung its praise and artists have delighted in its rhythmic
motion, but alas! the wheel as a commercial method of manufacture is
doomed to extinction. It cannot compete with the precision and speed of
machinery. It devolves, therefore, upon the artist potter to maintain
the wheel in its rightful place as, _par excellence_, the potter's tool.
No clay worker's studio should be without a wheel, but the particular
form of wheel depends upon the nature of the circumstances under which
it is to be employed.
The simplest wheel is that used by the Chinese. A circular plate with a
heavy rim is set upon a spindle so that it will revolve freely and run
steadily. As the workman sits or kneels upon the floor the surface of
the wheel is about at the floor level. Around the periphery and upon the
upper surface four holes are sunk and the workman, inserting a short
stick into one of these, gives the wheel a rapid motion. Then while it
is revolving by its own momentum the clay is centered and shaped. As the
motion is lost the stick is again inserted and the wheel spun. This
method, of course, involves much skill on the part of the workman.
In the next form, one which is only adapted, however, for crude
experimental work, the wheel is set upon the frame of a sewing machine
and operated by the treadle. A beginning may be made upon such a wheel
but the operator will soon wish for something better.
A common factory form and one which is well adapted for studio work is
the kick wheel. The wheel head is set at the top of a spindle and in the
upright shaft there is a crank to which is attached a horizontal moving
treadle. This is worked continuously by the left foot, the weight of the
body being supported by the right. The action is strenuous and scarcely
fitted for persons of other than robust physique but it can be used
successfully after practice. This wheel is made by the manufacturers of
potter's machinery.
Another form of the kick wheel is used in Europe and is, in fact, the
original wheel used by the French and German potters in the seventeenth
century. The head is set on a spindle as usual but instead of the crank
there is a large heavy disc on the bottom of the shaft and revolving in
a horizontal plane. This is within reach of the foot and the operator,
being seated, imparts a rapid motion by pushing, usually with the ball
of the right toe. The momentum is kept up by the weight of the disc and
there is a great advantage in that the foot need not be in continuous
motion. On the other hand it is difficult to acquire sufficient speed
and power for the work.
There are several forms of machine wheels which are entirely
satisfactory but which need the application of power. If a gas engine or
a water motor or electric current be available, every effort should be
made to obtain a wheel of this description. The prime motion is imparted
to a short horizontal shaft which moves at a constant speed. Then the
operator, seated in comfort, regulates the speed of the wheel itself by
pressure upon a treadle. No action is required but a simple pressure,
light for a slow speed and heavy for rapidity. Where the electric
current is available, nothing could be better. Self-contained
motor-driven wheels are available but are rather expensive.
One more plan may be mentioned in which the wheel is simply a vertical
lathe with a belt and handle to be turned by an assistant. This may be
convenient for some but it is not always possible to secure help at the
moment when the wheel is to be used. Moreover the cost of labor would
soon pay for a mechanical wheel.[G]
[G] Information as to the usual types of wheel may be obtained from The
Crossley Manufacturing Company, Trenton, N. J.; The Patterson
Foundry and Machine Company, East Liverpool, Ohio; a wheel operated
like a sewing machine is sold by the Lewis Institute, Chicago.
Whatever type of wheel is selected it should be arranged with a head
which can be removed. There are two methods of constructing this; the
head may be screwed on to the spindle, or the latter may terminate in a
cone-shaped plug upon which the wheel head is made to fit as in the
illustration (Fig. 14). The latter plan is to be preferred as the head
can be removed more quickly and is not so likely to work loose. Several
heads for the wheel can then be provided, one for regular work, one for
making plates, one for finishing and so forth.
The regular operation performed upon the wheel is termed either throwing
or turning according to the industry in which it is employed, but in
this description the word "throwing" will be used because the subsequent
operation in which tools are employed is best described as turning.
The best head for the wheel to be used in throwing is made of hard wood
or brass because the ball of clay can be easily centered upon a smooth
surface. This, however, involves that the work shall be cut off with a
wire and removed while soft. This is commonly done by professionals but
is beyond the skill of the beginner. It is best, therefore, to use a
head like that illustrated for plate making and to have a number of
specially shaped plaster bats to fit the recess (Fig. 17). Then when the
piece is formed, the bat with its burden can be set aside for the work
to harden.
[Illustration: Fig. 17. Wheel head with detached bat.]
Throwing is not an easy operation to describe but the following
instructions in the form of lessons will, with a large amount of
practice, enable the student to become fairly expert. Every opportunity
should be taken to watch a good potter at work. There are a thousand and
one little tricks in the position of the arms, hands, thumbs and fingers
which are impossible to describe but which can easily be copied. If a
kick wheel be used some time must be given to practicing the motion
without using clay. The action of the foot must become subconscious or
automatic like the pedaling of a bicycle so that simply to will a change
of speed is to accomplish it.
[Illustration: Fig. 18. The progress of a clay ball on the wheel.]
_Lesson I._ Take the bat about to be used, plunge it in clean water and
soak it nearly, but not quite, to saturation. If the bat remain wet one
minute after being taken from the water, it has soaked too long and must
be dried off a little. The effect of a wet bat is that the clay slips
and cannot be held in one place. The proper dampness is secured when the
clay ball can be pushed along the surface of the bat but does not slip
easily. This condition is important and should be secured by experiment,
because if not right, good work will be impossible.
[Illustration: PLATE I. THROWING.--LESSON II, 1.]
[Illustration: PLATE II. THROWING.--LESSON II, 2.]
_Lesson II._ Place a small basin of water close at hand. Take a ball of
clay about three inches in diameter. Set it on the center of the wheel
as nearly as can be judged. Now spin the wheel at a fairly rapid rate.
Brace the left elbow against the side and, wetting the hand, press the
ball of the thumb and the lower part of the palm against the clay. The
left forearm being kept rigid, the clay as it revolves will be forced
into the center of the wheel. Use the right hand to sprinkle water on
the clay that proper lubrication may be maintained. With the fingers of
the right hand pull the clay towards you, at the same time pressing
inward with left hand and so squeezing the clay. As the hands come
together the clay will rise in a cone. Do not pull it upwards but let it
rise as it is squeezed. Now bring the hands over the top and with the
thumbs together press down again. Lumps and irregularities will be felt
in the clay and the operations of spinning up and pressing down must be
continued until these disappear. Repeat the exercise of centering with a
fresh ball of clay until it can be accomplished with ease and rapidity.
The clay so used is not wasted. The superfluous water may be dried off
upon a plaster bat and the clay wedged up for use again.
[Illustration: PLATE III. THROWING.--LESSON II, 3.]
This wedging or waging of clay--the word has descended from the old
English potters--is important. A strong table should be built of which
the top, measuring about 30 by 20 inches, is made of two-inch plank. A
raised edge two inches high is fastened firmly by being nailed to the
sides; the trough thus formed is then filled with plaster and allowed to
harden. An upright post is fastened in the center of one side and from
the top of this a fine brass wire is stretched to the other side of the
table, thus making a diagonal. The worker stands at the side of the
table opposite the post. The ball of clay is taken in both hands and cut
in two against the wire, then the pieces are slapped smartly upon the
plaster, one on top of the other. The whole lump is then lifted, cut in
two and slapped down as before. The lump of clay is thus formed into
layers, the irregularities in hardness are corrected and the clay made
smooth. A little practice will make the work quite easy but it will
often be found necessary to cut and beat the clay fifteen or twenty
times before a good texture is secured. If the plaster table be dry the
clay will be stiffened rapidly but the plaster may be made wet to
prevent this if it should not be necessary. A clay may also be softened
in this way by sprinkling it with water as the wedging goes on.
[Illustration: PLATE IV. THROWING.--LESSON III, 1.]
[Illustration: PLATE V. THROWING.--LESSON III, 2.]
_Lesson III._ Center the ball as in Lesson II and moisten both hands and
the clay. Grasping the clay lightly but with sufficient force, press the
right thumb downwards and towards the palm and a cup-shaped hollow is
formed in the clay. Raise the right hand slowly, still keeping a light
pressure upon the clay with the thumb. The clay wall will rise with the
hand. Now insert the two first fingers of the left hand into the hollow
and hold them against the right-hand wall. Slacken the speed of the
wheel a little. Bend the forefinger of the right hand and press the
second joint and the knuckle against the outer wall so as to oppose the
fingers which are inside. Press the thumbs together to steady the hands
and raise both hands upwards together. The fingers inside and outside
the clay should be kept at a definite distance apart so that as the
hands rise, the clay is brought to a uniform thickness. The hands are
brought steadily to the full height to which the clay will go and thus a
cylinder is formed.
Repeat this lesson three or four times with fresh clay.
[Illustration: PLATE VI. THROWING.--LESSON IV, 1.]
[Illustration: PLATE VII. THROWING.--LESSON IV, 2.]
_Lesson IV._ Keep the hands wet. Shape the clay cylinder as directed in
the previous exercise. Now repeat the action of the fingers inside and
outside and, beginning at the bottom, take a closer grip of the clay and
draw up the walls as before. The cylinder is now taller and the walls
thinner. Do this again and again taking a little closer grip each time
until the cylinder is as tall and as thin as the clay will bear. The
walls will probably spread as the work proceeds and the hands must then
be used outside. Grasp the clay with both hands and squeeze it slightly;
at the same time raise the hands upwards. This will reduce the diameter
of the cylinder and thicken the walls. The operation of the fingers can
then be repeated until the full height is reached. There is, of course,
a limit to the height of the cylinder which can be made from a given
lump of clay and it is best to begin on a small scale. A ball of clay
which can be easily grasped with the hands is the proper size with which
to learn. A very small ball is nearly as hard to work as a large one.
Repeat this lesson until a tall cylinder can be made with ease and
certainty.
[Illustration: PLATE VIII. THROWING.--LESSON V.]
_Lesson V._ Keep the hands wet. Spin up a cylinder with thick walls as
in Lesson III. With the fingers of the one hand inside and those of the
other hand outside, open the cylinder gradually. Keep the wheel at a
slow speed. If the edge runs unevenly, use both hands outside to steady
it, then work outwards again until a shallow bowl is formed.
[Illustration: PLATE IX. THROWING.--LESSON VI, 1.]
_Lesson VI._ Keep the hands wet. Spin up a cylinder of medium height as
in Lesson IV. With the fingers of the right hand outside press inwards
at the base of the cylinder close to the bat and with the fingers of the
left hand inside, press outwards at a slightly higher level. This will
reduce the diameter at the bottom and increase it in the middle, making
a cup shape. Now raise the right hand and gently draw the top inwards.
With the left hand inside press the upper edge outward and with the
fingers of the right hand shape the upper part into the form of a jar or
flower pot.
[Illustration: PLATE X. THROWING.--LESSON VI, 2.]
[Illustration: PLATE XI. THROWING.--LESSON VII.]
_Lesson VII._ Keep the hands wet; proceed as in Lesson VI. Instead of
making the top flange outwards, draw it gradually inwards into a globe
form. Work the clay carefully upwards and inwards until the opening at
the top is almost closed. Several attempts will probably have to be made
before this result can be secured.
[Illustration: PLATE XII. THROWING.--LESSON VIII, 1.]
_Lesson VIII._ Keep the hands wet. Spin up a globe shape with a narrow
base as in Lesson VI but carry a good share of the clay to the top so
that the upper edge of the globe is quite thick. Insert two fingers of
the left hand and with the fingers of the right hand outside work the
upper edge of the globe into a tall neck. The action is the same as in
the shaping of a cylinder except that the diameter is smaller. A good
deal of practice will be necessary in order to keep the neck thin and to
raise it to any appreciable height, but perseverance will accomplish it.
[Illustration: PLATE XIII. THROWING.--LESSON VIII, 2.]
These lessons if carried out conscientiously will enable the operator to
produce almost any form in so far as the manipulation of the clay is
concerned but the work up to this point is drill only. It is not
intended that the pieces should be preserved. The next point is to
insist that the clay obey the potter in the shaping of a form.
A simple drawing of a jar should be made exact to the size proposed. Two
or three pairs of calipers are provided and with them the diameter of
each part of the drawing is taken. Of course a single pair could be made
to serve, but it is very inconvenient to change measurements while
working. A piece of wood also is cut to the height of the proposed
piece. The throwing is begun as usual by making a cylinder. This should
be higher than the drawing for the clay sinks in the shaping. First the
bottom is pressed into the proper size (Lesson VI). Then the body is
enlarged to the required measure and, lastly the diameter of the top is
taken and the height brought to the determined point. If too high the
superfluous clay may be cut off with a pointed knife, the edge being
carefully rounded afterwards.
It is only by checking up one's work in some such way as this that real
power can be acquired. The skilled worker can think in the clay and
create forms at will upon the moving wheel, but for the beginner to
attempt this is like an endeavor to paint pictures before one has
learned to draw. Shape after shape should be designed, drawn to scale
and thrown to measure; in fact, for elaborate pieces no other course is
possible.
CHAPTER X: TURNING
It is not possible to finish work to perfection in the operation of
throwing. The clay is too soft to handle and for proper finishing the
piece must be turned over to get at the bottom. An experienced thrower
reduces the final work to a minimum and this, of course, is the ideal
plan but even in factory practice every thrown piece is passed on to the
turner so that the phrase "thrown and turned" is used as of a single
operation, though it, in fact, expresses not only two processes but the
work of two men.
The artist-potter must needs, therefore, learn to turn, though this
process should not be worked to death as it is liable to be. Many
persons in the pride of having produced some sort of a form on the wheel
will leave it in the crudest possible condition and trust to the turning
tool to remove defects. If the lessons on throwing have been
conscientiously carried out, this error will not be committed.
A half dozen cylinders of convenient size should be thrown on separate
bats and set aside in a cool place to harden. They must not be dried but
should be in the condition known as "leather hard." If thrown one day
they will be ready for turning the next morning. Pieces thus hardened
are no longer flexible. They can be handled freely and the clay can be
easily cut with a knife.
[Illustration: Fig. 19. Turning tools bent and sharpened.]
The equipment for turning consists of a board support, a turning stick
and a set of tools. The board is of soft pine, eight or ten inches wide
and two feet high and is set upright at the back of the wheel frame
opposite the workman. It may be screwed in position if it does not
interfere with the throwing, or it may be set in a socket so as to be
removed when not in use. Its purpose is to support the end of the
turning stick. The stick is an ordinary broomstick in the end of which
is a sharpened nail. In use the end of the stick is held in the left
hand and the point is pressed into the board at any required height. The
right hand, holding the tool, is rested on the stick just as the hand of
a painter rests on the mahl-stick.
The turning tools are of soft steel.[H] They are purchased unshaped and
the potter must learn to bend and file them to suit himself. A section
of bench should be set apart for filing and care must be taken that the
steel dust does not get into the clay.
[H] The Milligan Hardware Company, East Liverpool, O.
One of the cylinders, with the bat upon which it was thrown, is now
taken in hand. Many beginners try to turn their pieces without detaching
them from the bat, trusting to the original adhesion to hold the piece
in position. This is a very unsatisfactory plan. A fundamental principle
in craft work is that the mechanical difficulties in manipulation should
be met and overcome at the first. If one trusts to some method which is
apparently easy one walks with crutches and there will come a time, if
progress is to be made, when such helps must of necessity be abandoned
and then the learning must be begun again. Therefore the student is
advised to face the mechanical technique at the very beginning. The
cylinder may be turned on the throwing bat, but there is a better way.
The piece should not become so hard that it will release its hold on the
bat but with a long bladed knife it should be cut away. If the knife be
held close to the bat a separation is easily effected. Set the
leather-hard cylinder upon a new bat which is slightly damp and which
runs true, on the wheel. The first problem is to center the work. A
pencil line may be run upon the bat making a circle just the size of the
cylinder. Then as the wheel is revolved it will be seen if the piece
runs true. It is quite unlikely that this will be the case. Perhaps the
bottom is true but the top circle is untrue. In other words, the axis of
the cylinder is not upright. Turn the cylinder upside down and try if it
will run any better. If it does the work may be begun in this position.
If it does not, turn it back again. Now take a pencil and hold it with a
steady hand so that it just touches the near side as the wheel goes
round. Lift up the edge of the cylinder on the side marked by the pencil
and slip a morsel of clay under it. Revolve the wheel and try with the
pencil again. In this way raise or press down one side, keeping the
bottom circle in the center until both top and bottom are running as
nearly true as they can be made. This, so far, refers only to the
horizontal planes. If one side is higher than the other it does not
matter at present. Now take three small pieces of soft clay, and,
holding the cylinder firmly with one hand, press them down at
equidistant points in the angle where the piece joins the bat. This
serves to hold the work in position. A square turning tool of small size
is the best to begin with. It is held in the fingers as a pen is held
but more firmly. The right hand rests on the turning stick and, the
connection between hand and stick being as rigid as possible, both are
moved together. This is better at first than moving the right hand
freely for to do so will surely result in irregular work.
The tool should be held so as to cut with one corner at first and it is
well to take one cut, remove the tool, take another cut and so on. The
object should be to feel the clay and to test its resistance. No one can
be a successful potter who does not cultivate a sympathy for the clay.
The tool is to cut, not to scrape. That is, the cutting edge is to be
opposed to the revolving clay. The point at which the tool touches the
clay is opposite the center or at the same distance from the operator as
the center of the wheel is. If nearer to the workman the tool will not
cut; if further away, it will scrape and pull (Fig. 5, page 50).
The first efforts should be directed towards acquiring skill. The
student should endeavor to make a cut at any desired point without
regarding the effect upon the shape of the cylinder. In other words the
clay is used merely as a practice piece. It is not to be preserved. It
is a good plan to keep on turning the first piece until it is all turned
away. Too many students fail because they wish to have a piece to keep.
He will make the best ultimate success who cares nothing for the
preservation of a dozen or two cylinders or other shapes, but uses them
merely as exercises in manipulation. If the student is over anxious to
avoid spoiling his work, he grows nervous and so loses control of his
tools and material. To set no value on the practice pieces themselves
begets confidence and this is the surest aid to success.
After two or three cylinders have been centered to the pencil line the
attempt to center one free-hand may be made. Place a cylinder on the
wheel but not quite in the center. Spin the wheel at a medium rate. Fix
the attention upon the eccentric motion, trying to forget the circular
motion. As the cylinder appears to move from side to side tap it lightly
with the hand so as to drive it towards the center. In all probability
this will result in driving the cylinder off the wheel altogether. Some
little practice is needed, but if persevered in the result will be a
power of convenient and rapid centering which is never forgotten and
which is the greatest possible help to successful work. One may practice
with a wooden cylinder or even a tin can if the weight approximates that
of the clay pieces.
[Illustration: Fig. 20. Turned feet. _A B C_, feet for small pieces. _D
E F_, feet for large pieces. _G H I_, common faults in foot finish.]
Accompanying the practice in turning there should be some exercise in
the shaping and filing of tools. Broad tools filed to the proper curve
are indispensable in finishing concave surfaces. A curved edge may also
be put upon one or two narrow tools. These will cut more rapidly than
the broader ones but will not leave as smooth a finish. Whatever tool be
used the final surface must be worked over with a soft sponge and water
so as to eliminate the tool marks and leave a plastic surface. One of
the principal troubles with which the beginner will meet is the
vibration of the tool known as "chattering." This is sometimes so slight
as not to be felt by the hand but when the motion of the wheel is
stopped the work will be found covered with fine ridges like gathering
on muslin. The way to prevent this is to avoid using the broad edge of
the tool until some experience has been gained. The way to cure it is to
go over the work again with a fine pointed tool and then to use the
sponge liberally. The point of the tool cuts through the small ribs or
wrinkles whereas a broad tool would ride over them and make the trouble
worse.
While the whole surface of the work will probably need more or less
turning, the chief part of the operation is concerned with the under
part or foot. The formation of a good foot marks a good potter and vice
versa. Before beginning to turn it should be decided what kind of a foot
is desired. Each shape has its own style. Some sketches are given here
with an idea of the form to which each is adapted. They are shown upside
down because the work is done in this position. The small bevel at the
outer angle is used for facility in glazing. A foot finished thus always
has a neat appearance when the glaze has been removed from the beveled
face.
CHAPTER XI: MAKING LARGE PIECES
There is a limit in size beyond which the non-professional will not be
able to go. Men of life-long experience can throw very large jars but
this involves not only more practice than the artist-potter can hope to
secure but also great physical strength. On the other hand it is
perfectly possible to form vases two or three feet in height by doing
the work in parts or sections. No one need fear to put such a plan in
operation on account of sentiment. It is, of course, worth while to make
large wares in a single piece but section work involves great skill and,
as a rule, the result attained is better. Work made in one piece is apt
to be badly finished, especially inside, and unduly heavy. Work made in
sections can be thrown with thin walls and finished with proper care. If
tradition be of any help, be it known that the Chinese have used the
piece method for hundreds of years, and that the Greeks used it three
thousand years ago.
The first requisite is a drawing either actual size or properly scaled.
The measurements should be those of the soft clay and if a particular
size be desired in the burned piece, the shrinkage, probably about
one-eighth, must be added. The drawing must show the size of each
section with the points of junction, and should indicate the upper and
lower edges in each case. Some divisions are best made right side up;
some are more easily thrown upside down. Care should be taken that the
faces which are to be joined are thrown under similar conditions. In
every piece of work one face rests on the bat, the other is in the air
or free. A bat face should always be joined to a bat face and a free
face to a free.
Suppose, for instance, a vase is to be sixteen inches high and is to be
thrown in four divisions of four inches each. The bottom division is
made first. This will stand in its normal position, right side up. The
second section must now be thrown upside down, because, if it were not,
its bat face would be joined to the free face of the first piece. So the
sections are thrown alternately, every other one being inverted.
[Illustration: PLATE XIV. MAKING LARGE PIECES. THE FIRST SECTION.]
As the pieces are thrown they must be carefully measured to see that the
faces which are to be united are the same size. The height of each piece
also must be gauged and adjusted. The bats with their contents are now
set aside to harden. As soon as they can be handled with safety the clay
pieces should be removed from the bats upon which the throwing was done
and set upon dry bats which will absorb the moisture and help to stiffen
the clay. It is a good plan to pile the sections up as they are to stand
in the finished piece, one upon another and to leave them so in a cool
place for ten or twelve hours. The faces which are to be joined will
thus acquire a uniform hardness and unequal shrinkage will be avoided.
When all is ready for the turning, the sections being of the proper
hardness are taken in hand. This work should not be hurried. It will
take a whole morning to put together a large piece. First, the bottom
section is placed on the wheel, centered and made to run true as regards
the top edge. It is then inverted and the foot is properly finished,
signed and dated. Then the second joint is likewise turned true on both
faces, the inside turned smooth; and so on, each piece in turn is
prepared for the fitting, the measurement of each face being accurately
adjusted. At this stage it is possible to correct the diameter of the
faces to some extent either by pressure as the wheel revolves or by
building up with soft clay. In either case, however, the new work must
be hardened before proceeding. The whole piece is now put together
carefully but with dry joints. It should be slowly revolved on the wheel
and the proportions carefully criticised. If satisfactory it is taken
apart again and the actual fitting up may proceed.
The bottom section is again centered most carefully on the wheel and
steadied with three pieces of clay. A thick slip is now prepared, the
same clay as that used for the work being of course, used. This slip
must be quite free from lumps and should be as thick as molasses. The
upper edge of the work is carefully sponged with clean water and a good
coating of slip is applied at the junction. Care must be taken that
every part of the face is covered with slip. The second joint is now
moistened at the junction and set in position upon the bed of slip. It
is placed very lightly and the wheel is gently revolved to see if the
running is true. If so it is pressed home and the superfluous slip is
removed. The joint should be quite close like a glued joint in
carpentry.
In the same way the third section is placed upon the second and the
fourth upon the third. It is now possible to work over the face of the
vase with a little soft clay. There is almost always some irregularity
in the line, especially at the joints, and this must be adjusted while
the work is moist. Then the whole face is gone over with turning tools
and sponge and the vase is set aside to dry. It must not be expected
that large pieces, made by any method, will be produced with as much
ease as small vases and bowls. The risks are much greater and, owing to
the size of the work, the faults are much more apparent. When the vase
is perfectly dry it should be set on the wheel, centered and slowly
revolved. If it is very untrue in its motion there is no remedy. It
should be broken down and the clay used again. A very slight
irregularity may be corrected by rubbing off a little clay on one side
of the foot but this cannot be done to any considerable extent. The
courage to break unsatisfactory work is never more valuable than at this
juncture. It will pay in the end, for no imperfect piece can be a source
of satisfaction to the conscientious craftsman.
[Illustration: PLATE XV. MAKING LARGE PIECES. Measuring the Foundation
of the Second Section.]
[Illustration: PLATE XVI. MAKING LARGE PIECES. Drawing up the Second
Section.]
[Illustration: PLATE XVII. MAKING LARGE PIECES. Shaping the Third
Section.]
[Illustration: PLATE XVIII. MAKING LARGE PIECES. The Three Sections
Completed.]
[Illustration: PLATE XIX. MAKING LARGE PIECES. Turning the Edge of the
First Section. (Note the other sections on the table.)]
[Illustration: PLATE XX. MAKING LARGE PIECES. Finishing the Bottom of
the First Section. (Note the second section in the foreground ready for
turning.)]
[Illustration: PLATE XXI. MAKING LARGE PIECES. Checking the Size of the
Second Section.]
[Illustration: PLATE XXII. MAKING LARGE PIECES. Fitting Together Dry.]
[Illustration: PLATE XXIII. MAKING LARGE PIECES. Setting the Third
Section in Place.]
[Illustration: PLATE XXIV. MAKING LARGE PIECES. The Three Sections Set
Together in the Rough.]
[Illustration: PLATE XXV. MAKING LARGE PIECES. The Finished Vase.]
CHAPTER XII: CUPS AND SAUCERS AND PLATES
It is not likely that many craftsmen will care to produce table wares or
even that they will be able to acquire the necessary skill. Simple as
these wares seem, they are, in fact, the most difficult of all to make
well. In factory working, one man makes nothing but cups, another
saucers and another plates, so that each attains the skill of constant
practice, but this is out of the question for the studio worker. At the
same time it is well to know how it is done and it may be that some one
will undertake to produce a few pieces for the sake of the enjoyment
arising therefrom.
It is possible to finish a cup upon the wheel just as a vase is made.
The handle is modeled in clay and fastened in place with slip when in
the leather hard condition. Saucers and plates cannot be made in this
manner; first, because the broad thin bottom will surely crack and,
second, because it is impracticable to turn a plate or saucer over in
order to finish the bottom. The risk of breakage is so great that there
is nothing to be gained.
If cups be needed of uniform size they must be molded. The making of the
molds has already been described. A small cylinder of the proper size is
thrown in clay and removed from the wheel while soft. A number of these
should be made at one time so as to avoid changing the wheel head often.
When all are ready a hollow head shaped to receive the cup mold is set
on the wheel and a mold inserted. One of the soft cylinders is now
lowered gently into the mold and as the wheel is revolved the soft clay
is pressed firmly against the walls with the fingers. A piece of wood,
called a rib, cut to the exact shape of the inside of the cup, is used
to smooth off the interior. The top edge is cut off and rounded and the
mold is set aside for the cup to harden. As soon as the cup can be
turned out it is set upside down upon the wheel and the bottom turned.
Another method dispenses with the formation of the cylinder or "lining."
A ball of clay of the proper size is dropped into the mold and pressed
into shape with the fingers, the wheel, of course, being spun. The
finishing is accomplished with the rib as before. This method will
answer for wares which are to receive a low fire but for high
temperatures the clay must be handled by the first-named plan.
The cup is not complete without a handle. This may be modeled as already
stated but to make each one of half a dozen in this way is unduly
tedious. The better plan is to model a handle in wax and make a mold as
already directed. A roll of soft clay is then laid in the mold, the two
halves pressed together and the handle taken out and finished. Care must
be taken that cup and handle are of the same degree of moisture, leather
hard, for choice, or they will part company as they dry. The fastening
is done with thick slip.
The method for saucers is the same as that for plates, so that one
description will suffice. The first step is to make a tool or profile. A
large handful of soft clay is rolled out into a thick cylinder and laid
down upon the plate mold. It should extend from the center to the
circumference, forming a radius of the circle. The clay is pressed
closely to the surface of the mold and part of it is squeezed into a
knob which will form the hand-hold of the tool (Fig. 16, page 66). The
clay is left in this position until it becomes nearly but not quite dry.
It is then taken off and whittled into shape. The front edge must be
straight and must lie along a radius of the plate. The foot is cut in at
the proper point and a broad wedge-shaped hollow is made so as to gather
the clay and pile it up into the foot. The hand-hold is shaped so as to
fit comfortably between the first and second fingers of the right hand.
When properly shaped the tool is thoroughly dried and then burned in the
kiln. The fire must not be severe as it is important not to shrink the
tool to any great extent. After burning slight corrections can be made
with a file or a hard stone. The heel of the profile must be exactly at
the center of the plate and the toe or curve must rest on the outer edge
of the plate mold.
In making plates a "batting block" and "batter" are used. The former is
a heavy block of plaster which is fixed to a strong table. It must be
saturated with water when in use. The wedging table already described
will serve for this. The batter is a disc of plaster to which a handle
is attached. It may be made of a thick plaster block, the handle being
cut out of the substance itself. This is also kept saturated with water
so that the clay will not stick. A ball of clay is laid on the block and
gently beaten out with the batter into a disc of the proper size and
thickness. The face of this is then polished with a steel blade and the
disc is then lifted, turned over and laid, polished side downward, upon
the mold. The wheel is then revolved and the clay pressed firmly to the
mold with wet hands. The tool is now dipped in water and pressed
steadily upon the revolving clay. The heel must be adjusted accurately
to the center and the foot will be seen to rise up in its proper place.
The operation is not easy and many failures must be expected but
practice will accomplish the desired result. When leather hard the plate
is gone over with a thin piece of rubber and when quite hard it may be
removed from the mold. The edge is now trimmed and the face sponged over
and the plate is ready for the kiln.
CHAPTER XIII: CASTING
In commercial production the casting method is constantly used. It is a
means of making light and delicate pieces with ease and, of course, all
the pieces cast in the same mold are alike. This very fact, however, has
led to the method being disregarded by the studio worker who does not
wish to duplicate anything that he makes. If a single piece only is to
be made the work involved in molding is a waste of time and it is better
to strive for skill at the wheel, and yet there are occasions when a
knowledge of casting is of great value. In the preparation of trial
pieces there is no method better. To make these in sufficient number on
the wheel would be tedious except for the benefit of the practice
involved.
Directions for making molds have already been given and the slip which
will have been prepared in the process of clay making is ready for the
casting process. This slip should be thick, about the thickness of
buckwheat batter. To be accurate, a pint should weigh 26 ounces. For
small pieces or for vases with narrow necks it is advisable to use the
slip rather thinner. For large wares, on the other hand, or for open
bowls it may be slightly thicker. A few experiments will show the reason
for this. Two quart jugs are needed. They should be large of neck and
should deliver their contents freely and completely. Jugs with a deep
shoulder are not good as the slip hangs in the pouring. One of these
jugs is filled with slip which is to be poured carefully from one to the
other, allowing it to flow gently down the side. This is to break the
air bubbles which are nearly always found to be present and the pouring
should be repeated until the slip flows smooth and even.
The mold, being thoroughly dry, is tied around with twine, if in parts,
and wedged firmly so that it cannot leak. The slip is then carefully
poured so as not to touch the sides and the mold is filled until a small
mound of slip rises over the edge. This mound will at once begin to sink
as the water is drawn into the walls of the mold and slip must be added,
little by little, to make good the loss. A small quantity of clay will
now be found to have stiffened at the rim of the mold and if this be
carefully removed with a steel tool the thickness of the wall of the
vase will be seen. If not thick enough the mold must be continually
filled up until the necessary thickness is attained. The mold is then
carefully lifted, making sure that the bottom is held firmly, and the
slip is poured out. It should not be poured back into the casting-jug
but into another vessel.
The mold is now set upside down to drain. It should not be placed upon
the table but upon two sticks laid parallel so that the drip may hang
clear. Several molds may be filled in this way at one time and after
about twenty minutes the one first filled may be opened. The bottom is
gently detached and the upper part of the mold, consisting of two
halves, is laid upon the table on its side. A little gentle manipulation
will now suffice to lift the one half and the vase will be seen lying in
the other half as in a cradle. The clay is still very soft and must be
treated carefully. The half mold, with the contained vase, is taken in
the left hand and held nearly upright, the fingers below, the thumb on
the top. Now set the fingers of the right hand under the bottom of the
vase, rest the thumb lightly against the side and tilt the half mold
gently forward. If mold and clay are in good condition the vase will
fall forward to be supported on the fingers of the right hand and
steadied by the thumb. The half mold is now laid down and the vase taken
in both hands, set gently on a plaster bat and put aside to dry. It
often happens that the vase leaves the mold with reluctance. If the slip
be very new, or the mold either damp or hard or worn out there will be
some difficulty in effecting a separation. By allowing the work to stand
a while, however, and by slightly jarring the mold from time to time
with the ball of the thumb the piece can generally be removed without
damage.
In using a new mold it is customary to make what is called a "waste
filling." The mold is filled with slip and at once emptied. After
standing a few minutes it is forcibly opened and the thin layer of clay
inside is picked out with a ball of plastic clay pressed against it. A
tool should never be used as this will damage the face of the mold. If
the clay should stick obstinately a soft cloth used over the finger will
remove it. The reason for this waste filling is that it removes the scum
which occurs on all new molds.
Cast ware should not be touched until quite dry and then the spare at
the neck is carefully cut off, the seams scraped down and the whole
surface smoothed with fine sand paper and a soft cloth. Worn out linen
serves excellently for this purpose.
Cups and bowls, if molded, are made without spare at the top. In this
case great care must be taken to see that the edge is left clean and
smooth in the casting. The spare neck on a vase acts as a margin of
safety, as it is completely cut away in the finishing. If a piece has no
spare the edge must be left without blemish at the first.
CHAPTER XIV: TILES
There are two methods of making tiles, the dust-pressed method and the
plastic. The former is the more usual commercial plan but the appliances
for preparing the dust and the heavy presses necessary are not adapted
to studio work. The dust-pressed tile is, moreover, somewhat mechanical
in surface. It is not suitable for modeling or for any treatment but
those of glaze and color. The plastic tile, on the other hand, may be
treated by plastic methods and the surface offers a texture which
appeals strongly to the artist.
For the successful production of tile a special body is necessary.
Ordinary pottery clay is too close in grain and straight tile cannot be
made from it. Small square pieces, however, such as tesseræ, can be made
from any clay.
It is presumed that a pure white tile body is not required. For studio
work the most pleasing white surface is found in an opaque enamel, but
for the most part the craftsman will wish to work for colored tile. A
cream or buff body is all that is necessary, therefore, and the
foundation of this is a clay known as sagger clay. In order to secure
the necessary porosity a fine "grog" must be used. Grog is burned clay.
After working awhile there will be an abundance of this in broken
unglazed pottery but at first some soft fire-bricks must be pounded.
This is laborious work, but a boy can usually be hired to do it. The
brick or broken pottery is crushed in an iron mortar but should not be
broken too fine. Two sieves are necessary, one of 20 and one of 40
meshes to the linear inch. The coarse powder which passes through the 20
mesh and lies upon the 40 mesh is used. This is called 20-40 grog. The
dust which passes through the 40 mesh may be saved for kiln work. It is
useful for setting biscuit pieces one upon another as it will
effectually prevent sticking. This powdered grog is also useful in the
case of flowing glazes. A thick layer on the bottom of the kiln will
catch any drops of glaze and save the kiln from damage.
A quantity of the 20-40 grog having been prepared, a mixture should be
made of:--
Sagger Clay 550 parts
20-40 Grog 300 parts
Ground Flint 150 parts
The clay should be finely pulverized and the whole mixed in the dry
state. Water is then added, little by little, until a rather soft mass
is obtained. It is not practicable to mix clay of this description by
the slip method because the grog would settle out and fall to the bottom
of the vessel. It sometimes happens, however, that the stoneware clay
contains grains of iron which cause black spots to appear in the tile.
If these cause trouble the clay must be made into slip first and lawned
through 120 mesh. It is then allowed to become very thick and the grog
is stirred in. This is a good deal more trouble than the first named
plan and is not often necessary.
Tile are sometimes made in plaster molds. A tile of the proper size is
cut from a plaster block and a mold is made from it. If a modeled
surface be desired clay may be modeled upon the face of the plaster tile
before the mold is made. The mold will then receive the embossment in
reverse and all the tiles made from this mold will be alike. The clay is
pressed into the mold while quite soft and is scraped off level at the
back. Thus it is the face of the tile that is shaped by the plaster. If
this plan be adopted the tile must be removed from the mold as soon as
possible. If left to dry in the mold they will warp because of the
unequal absorption.
A better method has been devised by the author and has been put into
practice with considerable success. When the size of the proposed tile
has been determined a board is made which is large enough to hold a
square of the tile, say twelve or sixteen. Thus if a tile five inches
square is to be made the board would be fifteen by twenty inches for
twelve tile or twenty inches square for sixteen. On each side of the
board a wooden rim is fastened and this must stand higher than the board
to the exact thickness of the tile. About five-eighths of an inch is
enough. The board must be perfectly rectangular and marked off at even
distance of five inches and a shallow groove is cut at each point.
To make the tile the board is wetted and an even coating of grog dust is
sprinkled upon it. A ball of clay is laid in the center of the board and
rolled out with a rolling pin to fill every part of the frame. With a
straight edge the clay is struck off smooth and clean, working always
from the center outwards. Reversing the plaster mold method the tile are
now face upward and any kind of surface may be given at will. The clay
may be lubricated with water and made smooth or it may be sprinkled with
grog dust which will give a sandy or toothed finish. The square is now
to be cut into tile and this is done with a slender knife and ruler. The
ruler should not rest upon the clay but upon thin strips of wood or
cardboard which may be laid along the edges for the purpose. The cutting
should not go quite through the clay as, if a slight connection be
allowed to remain at the bottom, the tile will keep each other straight.
When the cutting is finished the board should be set at an angle of
forty-five degrees for the clay to harden. When leather-hard the whole
may be turned gently over and the tile allowed to fall on to a board
placed in readiness. They are now broken apart, trimmed if necessary and
set aside to dry.
Tile made in this way can be kept straight without difficulty and the
method is much more expeditious than pressing in plaster molds.
If a modeled surface be intended it is quite easy to work on the tile in
the tray while the clay is soft. Forms may be cut in wood and pressed
into the clay in any variety and the charm of individual treatment is
preserved.
The body given above will prove quite porous when fired but it will take
matt glazes well. A little crazing is no detriment to tile because they
are not like vessels which are meant to hold water. If a denser body be
wished for some of the flint may be replaced by spar.
One of the most attractive methods of decorating tile is by means of a
white or delicately tinted enamel and color. The opaque tin enamel given
on page 134 will answer well and if the whiteness prove too intense it
may be modified by a very small addition of under-glaze color according
to the tint desired. The tile should be glazed rather thick. Not as
thick as a matt glaze but thicker than bright glazes. The glaze or
enamel should be poured into a flat tray which is large enough to
receive one tile. The tile is taken by the edges between fingers and
thumb and held face downwards. Do not let either fingers or thumb
project beyond the face. The glaze having been well stirred the face of
the tile is allowed to rest upon it for about two seconds. The hand is
then lifted quickly and reversed so that the tile is face upwards. Every
effort should be made to avoid streaks or tears and a little practice
will accomplish this. If the glaze shows a bad surface it should be
scraped off. It can be mixed up and used again. Sometimes a slight
wetting of the tile before glazing will help the surface to flow evenly.
The decoration is carried out with ordinary under-glaze colors. These
may be mixed together to produce any hue which is sought and a little of
the glaze itself, about ten per cent., should be mixed with the color.
This will assist in uniting the color with the glaze so that they melt
together.
To produce enamel decorations at their true value the color should be
painted upon the dry glaze before it is burned. The best relation
between surface and color is thus secured. The color must be worked
quite thin with water and a little glycerine. A quick, sure stroke is
needed as no change or erasure is possible. The design may be made on
paper and traced or pounced on to the glaze with lamp-black.
For burning the tile there is nothing better than little fire-clay
boxes. These can be made in a mold without difficulty and the inside of
each should be washed with glaze. If some such protection be not
provided dirt is almost sure to fall on the flat surface and the tile
will be spoiled. It is not possible to rear them on edge in the kiln for
burning as then the glaze would flow to the lower side and cause an
unsightly ridge.
CHAPTER XV: GLAZES AND GLAZING
PART I
Much of the fascination of pottery making centers in the glaze. At one
time a great deal of mystery appeared to surround the composition and
use of glazes, but if one will take the trouble to learn, much of this
may be dispelled. Some knowledge of chemistry is desirable if an
understanding of the theory of glaze-making is to be acquired, but a
good deal may be learned even without this knowledge. Only such simple
instruction as can be assimilated by ordinary intelligence will be
attempted here, as an exhaustive treatment of the subject would be long
and tedious.
It is possible to purchase glazes ready for use[J] but the true
craftsman will not be satisfied until he can prepare his own.
[J] The Roessler & Hasslacher Chemical Company, 709 6th Avenue, New
York City, manufacture glazes according to the recipes of the
author, and also chemicals for use in the laboratory.
Glazes[K] belong to a class of chemical compounds known as silicates;
that is, they have silica as the characteristic ingredient. Clear glazes
are compound silicates of lead, zinc, lime, potassium, sodium, aluminum
and boron. Matt glazes are characterized by certain of these ingredients
being present in excess; and stanniferous or tin glazes are, as the name
implies, rendered opaque by the use of oxide of tin.
[K] It is admitted that glazes are not chemical combinations but solid
solutions, but the principle is more easily understood when the
analogy of chemical action is adopted.
The commonest type of glaze is that which is made from ready prepared,
commercial substances. These are called raw glazes as being made from
raw materials or materials which need no preparation.
It is possible to mix a glaze in a druggist's mortar by hand, using fine
sieves, but if the best results are to be secured, a small mill must be
used for grinding. The best form of mill is the ball mill or jar mill.
This consists of a porcelain jar which is set in a frame and made to
revolve upon its axis in a horizontal position. It is about half filled
with porcelain balls and these as they roll against each other perform
the grinding. These mills may be purchased ready for use, either as a
single jar to be worked by hand or a battery of two or more revolved by
power.[L]
[L] Paul O. Abbé, 30 Broad Street, New York City.
A good pair of scales is a necessity and it will be found convenient to
use metric weights which need no calculation into pounds and ounces.
Suspended scales are not as easy to use as the form known as counter
scales or balances. They should have movable pans which are usually
nickel plated. Upon these the materials can be placed direct without the
use of pieces of paper, which are always troublesome and inaccurate.
There should be a graduated bar on the front for the adjustment of
weights of five grams and under. This avoids the use of small weights
which are always being mislaid and lost. Dealers in chemical supplies
keep these scales in stock and the cost is about eight dollars. A set of
weights must also be procured from one hundred grams to five grams
inclusive. These need not be of the accurate adjustment which are used
in analysis. A good inexpensive grade is sufficient.
The ingredients for glazes are given in the following list:
Commercial Chemical Symbol or Equivalent
Name Name Formula Weight
White Lead Lead Carbonate Pb(OH)_{2}2PbCO_{3} 258
Zinc Oxide Zinc Oxide ZnO 81
Soda Ash Sodium Carbonate Na_{2}CO_{3} 106
Niter Potassium Nitrate KNO_{3} 202
Whiting Calcium Carbonate CaCO_{3} 100
(Carbonate of Lime)
Feldspar Orthoclase K_{2}O,Al_{2}O_{3},6SiO_{2} 557
Kaolin Aluminum Silicate Al_{2}O_{3},2SiO_{2},2H_{2}O 258
or China Clay
Flint Silica SiO_{2} 60
Borax Sodium di Borate Na_{2}B_{4}O_{7}10H_{2}O 382
Boric Acid Boric Acid B_{2}O_{3}3H_{2}O 124
For coloring, the following metallic oxides are used:
Color Chemical Symbol or Equivalent
Name Formula Weight
Blue Cobalt Oxide CoO 80
Blue and Green Copper Oxide CuO 79
Gray and Brown Nickel Oxide NiO 75
Brown and Yellow Iron Oxide Fe_{2}O_{3} 160
Brown Manganese Carbonate MnCO_{3} 115
Under-glaze colors may also be used for coloring glazes, the color being
ground with the glaze batch.
It is not absolutely necessary to commit the formula and equivalent
weight to memory. They will soon be remembered as use becomes second
nature.
A glaze is usually expressed as the chemical formula. In this there are
three divisions given, each of which expresses a distinct function. On
the left hand are the bases, the foundation of the glaze. These indicate
the type, such as lead glaze, a lime glaze, an alkaline glaze, etc. All
glazes being silicates, this is the usual way of distinguishing them. In
the center are the alumina and boron oxide. These regulate the behavior
of the glaze in the fire. They make it viscous or sluggish as it melts
and prevent a too rapid flow. The alumina is infusible, the boron is
fusible, but boron cannot be used in a raw glaze for reasons to be
presently explained. At the right stands the silica, the dominating
factor with which all the other ingredients combine, and which controls
the behavior of the whole as regards the fitting of the glaze to the
body.
The very simplest form of glaze is a bisilicate of lead, represented by
the formula PbO, SiO_{2}, or one equivalent of lead oxide and one of
silica. The term "equivalent" means that the mixture is calculated, not
upon the actual weight of a substance but upon its equivalent or unit
weight. Thus the equivalent weight of lead oxide, PbO, being 222, in
order to produce the formula in actual weight 222 grams or pounds must
be weighed out. It does not matter what weights are used so long as they
are the same for all.
In like manner the equivalent weight of silica is 60 and as flint is
pure silica, the formula PbO, SiO_{2} would be produced by weighing--
Litharge or Lead Oxide 222 parts
Flint or Silica 60 parts
Litharge is not, however, a convenient substance to use. It is very
heavy and does not mix well in water. The most usual substance for the
introduction of lead oxide is white lead. This is not lead oxide but it
changes to lead oxide when burned. White lead bears the formula
Pb(OH)_{2}, 2PbCO_{3}, which, being dissected is found to be 3PbO,
H_{2}O, 2CO_{2}. H_{2}O is water and CO_{2} carbonic acid, both of which
pass off in burning. Both, however, are weighed when the white lead is
put on the scales and therefore the equivalent weight of white lead is
258 and not 222.
The mixture for practical purposes then would be--
White Lead 258 parts
Flint 60 parts
Which, when ground and spread upon the ware would be a very fusible
glaze of a yellowish tone.
This was spoken of as a bisilicate of lead because the measure of the
silica, also called the acidity of a glaze, is calculated upon the
oxygen contained in the base and the silica respectively. PbO contains
one molecule of oxygen, SiO_{2} contains two. Hence the relationship of
the oxygen in the base to the oxygen in the silica is as one to two.
This is called simply the "oxygen ratio" and is of great importance in
determining the behavior of a glaze. While this simple bisilicate of
lead will be a glaze under certain conditions it is found to possess two
faults. 1. It is too fluid under fire. The glaze will run down a
vertical surface and leave the upper edge of the piece bare. 2. If
subjected to a long slow fire it will lose its gloss and become
devitrified. This devitrification is often seen in commercial work and
appears as a dull scum in patches and around the edges of the ware. It
is, in fact, a crystallization of the silica which separates out, as
salt does from an evaporated brine. Both these faults may be corrected
by the addition of a little alumina to the glaze. A whole equivalent of
alumina would be too much, in fact it is found in practice that .2
equivalent is sufficient for most lowfire glazes. In order to maintain
the oxygen ratio and to keep the glaze as a bisilicate the silica
content must be raised. Alumina contains three molecules of oxygen so
that the total amount of alumina is multiplied by three and the silica
brought to the equal point thus:
PbO, .2Al_{2}O_{3}, 1.6SiO_{2}
The amount of silica required in any bisilicate glaze may be found by
the following equation:
SiO_{2} = 2(3Al_{2}O_{3} + 1)/2
Thus if the alumina content were .25 equivalent this would be expressed:
SiO_{2} = 2(.75 + 1)/2
Or--
SiO_{2} = 3.50/2 = 1.75 equivalent
Now in order to produce this as a mixture it would be possible to
introduce the alumina in the pure state, but pure alumina is expensive
and clay which contains alumina is cheap so that clay is generally used
to supply the alumina. Clay, however, contains silica as well, and
therefore allowance must be made for this. On referring to the formula
for kaolin, the purest form of clay, Al_{2}O_{3}, 2SiO_{2}, 2H_{2}O, it
will be seen that there is twice as much silica present in equivalence
as there is alumina and therefore .2 kaolin will contain .2Al_{2}O_{3}
and 4SiO_{2}. Subtracting, then, the 4SiO_{2} from the 1.6SiO_{2} needed
there will be 1.2 left to be supplied in the form of flint. The mixture
therefore is--
White Lead 1.0 × 258 = 258
Kaolin .2 × 258 = 51.6
Flint 1.2 × 60 = 72
This is a glaze of the same character as that first given except that it
no longer flows unduly from the higher places nor will it devitrify in a
long-continued fire. The alumina will have counteracted both these
evils.
A glaze with only lead oxide as the base is not, however, desirable for
general use. The color is yellowish and the lead oxide is apt to destroy
the hue of any colors which are used with it. The available bases may be
classified under three heads. 1. The metallic oxides, lead and zinc
oxides. 2. The alkaline earths, the oxides of calcium and barium. 3. The
alkalies, potash and soda. Barium oxide is not often used and soda
cannot be used in raw glazes because there is no convenient substance
which contains it. As glazes are always ground in water only insoluble
ingredients can be employed without preparation. Potash is found in
feldspar which is insoluble and while there is a so-called soda feldspar
it can rarely be obtained of sufficient purity.
In arranging the bases with which to compose a glaze it is desirable to
use one at least from each class, but it must be borne in mind that
however many bases are introduced the total must always be unity. This
unit is, for the sake of brevity, described as RO. For example the
following groups may be set forth:
1. PbO Lead Oxide .7
CaO Calcium Oxide .3
---
RO 1.0
2. PbO .6
CaO .4
---
RO 1.0
3. PbO Lead Oxide .5
ZnO Zinc Oxide .2
CaO Calcium Oxide .3
---
RO 1.0
4. PbO .6
ZnO .1
CaO .3
---
RO 1.0
5. PbO Lead Oxide .6
CaO Calcium Oxide .3
K_{2}O Potassium Oxide .1
---
RO 1.0
6. PbO .50
CaO .35
K_{2}O .15
----
RO 1.00
7. PbO Lead Oxide .45
ZnO Zinc Oxide .10
CaO Calcium Oxide .30
K_{2}O Potassium Oxide .15
----
RO 1.00
8. PbO .35
ZnO .15
CaO .35
K_{2}O .15
----
RO 1.00
The reason for the unit rule is that if one formula is to be compared
with another there must be a uniform basis upon which to work and,
furthermore, it makes no difference whether the silica combines with
one, two, three, or four bases, the chemical action is the same and, so
long as the sum of the bases is kept at unity, the same amount of silica
will be required.
If two glazes be taken as an illustration this will be made clear:
PbO .6 }
CaO .4 }
--- } Al_{2}O_{3} .2 SiO_{2} 1.6
1.0 }
PbO .46 }
ZnO .12 }
CaO .28 }
K_{2}O .14 }
---- } Al_{2}O_{3} .2 SiO_{2} 1.6
1.00 }
Both of these formulae are bisilicates and each being properly fired,
will stand, without crazing, on the same body.
The use of the formula is to give an insight into the composition of the
melted glaze. It takes no account of volatile ingredients or losses in
the fire but for this very reason it must be translated into the
substances to be weighed before use can be made of it.
Of the ingredients given on pages 142, 143, some contain but one item of
the formula, others contain several, as in the case of kaolin already
cited. Feldspar, of the variety known as potash feldspar and named by
mineralogists, "orthoclase," is a very useful ingredient in raw glazes,
being, in fact, almost the only source of potash. The formula, page 142,
shows that a molecule or equivalent of feldspar contains one molecule of
potash K_{2}O, one of alumina Al_{2}O_{3}, and six of silica SiO_{2}.
This fact is taken into account in calculating the mixture or batch
weight.
Base No. 5 (page 148), is as follows:
PbO .6
CaO .3
K_{2}O .1
----
1.0
And this made up into a bisilicate glaze would be:
PbO .6 }
CaO .3 }
K_{2}O .1 }
---- } Al_{2}O_{3} .2 SiO_{2} 1.6
1.0 }
These items are extended in a horizontal line, a space being left on one
side for the list of ingredients.
PbO CaO K_{2}O Al_{2}O_{3} SiO_{2}
.6 .3 .1 .2 1.6
Addition .6 White Lead .6
----------------------------------------
Subtraction .0 .3 .1 .2 1.6
Addition .3 Whiting .3
----------------------------------------
Subtraction .0 .1 .2 1.6
Addition .1 .1 .6 Feldspar .1
----------------------------------------
Subtraction .0 .1 1.0
Addition .1 .2 Kaolin .1
----------------------------------------
Subtraction .0 .8
Addition .8 Flint .8
----------------------------------------
Subtraction .0
Each item is thus disposed of until the list is complete. These figures
are, however, given in equivalents and each must be multiplied by the
equivalent weight of the substance used.
White Lead .6 × 258 = 154.8 parts by weight
Whiting (calcium carbonate) .3 × 100 = 30.0 " " "
Feldspar .1 × 557 = 55.7 " " "
Kaolin .1 × 258 = 25.8 " " "
Flint .8 × 60 = 48.0 " " "
-----
314.3 Batch of Glaze
These amounts are weighed out in grams, put upon the mill with half a
pint of water, and ground for about an hour. When taken off, the jar and
porcelain balls are washed with plenty of water and the washings saved.
The glaze, thus diluted, is strained through a lawn of 120 mesh and laid
aside to settle. The clear water is then siphoned or poured off and the
glaze is ready for use.
For glazing the glaze should be as thick as cream. A finger dipped into
it should show a white coating which cannot be shaken off. The pottery
to be glazed should be first soaked in clean water until all absorption
has ceased. It is then wiped dry and plunged into the glaze bath, or, if
the piece be large, the glaze may be poured over it. The piece is gently
shaken to distribute the glaze evenly and it is then set aside to dry.
Before glazing a piece everything should be prepared. A stilt or support
upon which to set the wet glazed pottery, and a bowl of water in which
to wash the fingers so as to save all the glaze. It will be found best
to glaze the inside of the piece first. It should then be well shaken to
remove as much glaze as possible before beginning the outside. A thick
glaze inside is almost sure to run down to the bottom where it will form
a pool and perhaps burst the piece.
Before firing, the bottom of the pottery should be carefully trimmed.
Any excess of glaze is removed and the point of contact with the table
is sponged clean. Then, when the piece is set in the kiln the bottom
will not be inclined to stick.
PART II: MATT GLAZES
The texture of the matt glaze is always pleasing and the artist is not
content unless at least some of his work can be finished in this way.
Matt glazes are not underfired glazes nor are they deadened by acid or
sand blast. They are produced in two ways. First, by an excess of
alumina which is believed to cause the formation of certain compounds in
the glaze, and, second, by an excess of silica which produces a
devitrified surface. It was mentioned in the last chapter that a glaze
free from alumina will devitrify or become dull. This is undesirable
when a glaze is intended to be brilliant but it may be controlled and
turned to advantage in the production of a certain type of matt. The
successful preparation of this silica matt is extremely difficult. In
fact, in the studio kiln it is almost impossible. These small kilns are
apt to cool with great rapidity whereas, in order to produce the silica
matt the kiln must be cooled very slowly, hours and even days of cooling
being sometimes necessary.
The alumina matt is more simple and its texture is quite satisfactory,
being, in the opinion of some, the more pleasing of the two.
It was mentioned in the last chapter that the best bright glazes for low
temperature work are bisilicates, having an oxygen ratio of 1:2. The
alumina matt has an oxygen ratio of about 3:4. This is secured in the
following manner. The RO content may consist of any of the bases used in
bright glazes, the proportion of each being adjusted in accordance with
the desired point of fusion. The alumina content is rather higher than
in a bright glaze and should not fall much below .3 equivalent, .35
equivalent is even better. The silica is adjusted in accordance with the
following equation:
SiO_{2} = 3(3Al_{2}O_{3} + 1)/4
Now if the alumina content be placed at .35 equivalent this would work
out:
SiO_{2} = 3(1.05 + 1)/4
Or:
SiO_{2} = 6.15/4 = 1.5375
But as such a complete fraction is not necessary it may be stated as
1.54 equivalent. The formula would therefore be:
RO, Al_{2}O_{3} .35, SiO_{2} 1.54
The RO content should not be too fusible. Lead oxide is desirable up to
about .5 equivalent and it is an advantage to use feldspar so that
K_{2}O may be introduced. Calcium oxide is also good but zinc oxide must
be used sparingly as it is apt to suffer if overfired. The high content
of alumina necessitates a good deal of clay and as this, if used raw,
would make the glaze too plastic and cause it to crack, it is best to
calcine a part of it, thus removing the combined water and changing the
equivalent weight from 258 to 222. The calculation will then proceed as
in the case of a bright glaze.
PbO .50 }
CaO .35 }
K_{2}O .15 }
---- } Al_{2}O_{3} .35 SiO_{2} 1.54
RO 1.00 }
PbO CaO K_{2}O Al_{2}O_{3} SiO_{2}
.50 .35 .15 .35 1.54
Addition .50
White Lead .50 × 258 = 129
----------------------------------------
Subtraction .0 .35 .15 .35 1.54
Addition .35
Whiting .35 × 100 = 35
----------------------------------------
Subtraction .0 .15 .35 1.54
Addition .15 .15 .90
Feldspar .15 × 557 = 83
----------------------------------------
Subtraction .0 .20 .64
Addition .15 .30
Calcined Kaolin .15 × 222 = 33
----------------------------------------
Subtraction .05 .34
Addition .05 .10
Kaolin .05 × 258 = 13
----------------------------------------
Subtraction .0 .24
Addition .24
Flint .24 × 60 = 14
----------------------------------------
Subtraction .0
The mix, therefore, is:
White Lead 129 grams
Whiting 35 "
Feldspar 83 "
Calcined Kaolin 33 "
Kaolin 13 "
Flint 14 "
This will give a silky matt glaze, nearly white, maturing at about cone
1. If a lower fusing point is desired the white lead may be increased at
the expense of the whiting or if the glaze prove too fusible the reverse
will correct it. The flint may be omitted without damage.
The grinding of a matt glaze is of great importance. It is better to
have it too coarse than too fine. Grinding for one hour on the ball mill
should be ample and if the glaze be then strained through 120 mesh lawn
all coarse particles will be arrested. A glaze that is too fine will
crack and peel off or will curl up in the kiln.
More than half the success of matt glazes lies in the using. It is
necessary that the coating of glaze be very thick or the true texture
will not be developed. When the glaze is taken from the mill plenty of
water may be used in order to wash the apparatus clean and to save all
the glaze. This is set aside in a deep bowl to settle. After some hours
the clear water is carefully drawn off with a siphon.
Half an ounce of gum tragacanth is put to soak in a quart of clean
water. After twelve hours the gum will have swollen to a jelly-like
mass. This is now worked vigorously with a Dover egg-beater or in a
Christy mixer and again set aside. After another twelve hours the
operation is repeated and the solution is a clear syrup of the
consistency of thin molasses. A drop or two of carbolic acid or other
germicide should be added to prevent decomposition. This mucilage should
be prepared in advance. To the glaze batch from which the water has been
removed a tablespoonful of the mucilage is added. If more of the glaze
than the single batch has been weighed out then more mucilage will be
necessary. The mixture is to be stirred very thoroughly and it will be
found to thicken under the hand. It must be very much thicker than the
bright glaze. In fact, the thicker it is the better, only that it must
flow sufficiently so that the pottery may be covered with a smooth
coating, avoiding lumps. Matt glazes do not correct their own faults in
the kiln as bright glazes do. Every finger mark will show and,
consequently, the glazing must be done with the greatest care. The
process is the same as that described for bright glazes, except that as
much glaze as possible is left on the ware. No more shaking should be
done than will suffice to secure a smooth coating. It is well to place
the pieces upside down to dry.
For the inside of the pieces a matt glaze may be used or a thin coat of
clear glaze at the pleasure of the worker. If the latter, care must be
taken that none of the inside glaze is allowed to run over the edge.
In firing, the pottery is sometimes placed on a stilt but this is not
absolutely necessary. For a support a flat piece of burned clay may be
used and this should be covered with an infusible wash to prevent any
possibility of sticking. Equal parts of kaolin and flint make a good
wash. The wash is worked up with water into a slip and applied with an
ordinary brush.
PART III: FRITTED GLAZES
Fritted glazes, like raw glazes, are clear and brilliant and for most
purposes the latter will suffice. Since, however, the aim of this work
is to give as complete information as may be the fritted glaze will not
be omitted.
A fritt is a melt or compounded glass and the purpose of it is to permit
the use of certain ingredients which are not available in the raw state.
As glazes are ground in water it is essential that the substances used
be insoluble. This condition would prohibit advantage being taken of
borax, boric acid, and soda ash, if it were not for the possibility of
rendering these insoluble by the operation of fritting.
The following is an example of a fritted glaze:
PbO Lead Oxide .30 }
ZnO Zinc Oxide .15 }
} Al_{2}O_{2} Alumina .15 }
CaO Lime .25 } } SiO_{2} Silica 2.65
} B_{2}O_{3} Boric Acid .40 }
Na_{2}O Soda .20 }
K_{2}O Potash .10 }
This will be produced in accordance with the usual calculation by the
mix:
White Lead .3 × 258 = 77
Zinc Oxide .15 × 81 = 12
Whiting .25 × 100 = 25
Borax .20 × 382 = 76
Feldspar .10 × 557 = 56
Kaolin .05 × 258 = 13
Flint 1.95 × 60 = 117
The borax contains the required amount of both soda and boric acid and
the potash is supplied by the feldspar. Borax, being soluble, must be
melted with certain other ingredients into an insoluble glass, thus:
Fritt:
Borax 76 x 2 = 152
Whiting 25 x 2 = 50
Feldspar 30 x 2 = 60
Flint 50 x 2 = 100
---
362
These ingredients are weighed out in double quantity to guard against loss
in melting and are fused either in the kiln or in a special furnace. A good
fritting furnace is the No. 15, made by the Buffalo Dental Manufacturing
Company. The charge is put into a plumbago crucible and when melted is
poured out into water. This breaks up the fritt and renders it easy to
grind. A similar crucible may be used in the kiln but as the fritt becomes
very hard when cold and a crucible must be broken each time, the furnace
method is better. If the fritt as given prove too sluggish to pour freely,
the feldspar may be omitted, being added, of course, to the glaze mix. The
melted weight of the fritt must now be calculated.
Borax contains in each equivalent 180 parts water. Whiting contains in each
equivalent 44 parts carbonic acid. Both water and carbonic acid pass off in
the melting, thus the 76 parts of borax will be reduced in weight to 40
parts, and the 25 parts of whiting will be reduced to 14 parts. Spar and
flint undergo no loss. The fritt after melting will therefore be:
Borax 40
Whiting 14
Spar 30
Flint 50
---
134
And the final mix for the glaze will be:
Fritt 134 parts
White Lead 77 "
Zinc Oxide 12 "
Feldspar 26 "
Kaolin 13 "
Flint 67 "
This is ground on the mill as already directed and is ready for use.
Fritted glazes are better than raw glazes for certain classes of ware.
They are usually whiter and less easily scratched. They are, moreover,
better for use with underglaze colors and are, as a rule, more easily
melted. It is never necessary to make a fritt for the preparation of
matt glazes.
PART IV: RECIPES
While the purpose of this work is not so much to put ready-made
materials into the hands of the craftsman as to enable him to work out
his own plans, it is recognized that there are some workers who lack the
training and even the patience to do this. For these, the following
recipes are given, but with the proviso that no recipe can be regarded
as perfect for all conditions. Just as an untrained cook can spoil a
dinner even when surrounded by cookery books, so the best of recipes
will fail when unskillfully treated. One must be prepared to recognize
the faults which are sure to develop and to correct them in an
intelligent manner. The previous chapters should therefore be carefully
studied, not alone for the information but because "the joy of the
working" depends greatly upon the knowledge one has of the operations
involved and a modest confidence in one's own powers.
1. Bright raw glaze.
Cone .06 Formula
PbO .60 }
CaO .25 } Al_{2}O_{3} .15 SiO_{2} 1.45
K_{2}O .15 }
Mix:
White Lead 155
Whiting 25
Feldspar 55.7
Kaolin 13
Flint 45
Grind, with one-half pint of water, for one hour.
2. Bright raw glaze.
Cone 1 Formula
PbO .45 }
ZnO .15 } Al_{2}O_{3} .20 SiO_{2} 1.60
CaO .25 }
K_{2}O .15 }
Mix:
White Lead 116
Whiting 25
Zinc Oxide 12
Feldspar 83
Kaolin 13
Flint 36
3. Bright fritted glaze.
Cone .02 Formula
PbO .25 }
ZnO .15 } Al_{2}O_{3} .15 }
CaO .30 } } SiO_{2} 2.35
Na_{2}O .20 } B_{2}O_{3} .30 }
K_{2}O .10 }
Mix:
Fritt Glaze
Borax 114 Fritt 117
Whiting 60 White Lead 64
Soda Ash 10 Zinc Oxide 12
Spar 56 Spar 28
Flint 78 Kaolin 13
Flint 60
Grind as before.
4. Matt glaze.
Cone .02 Formula
PbO .50 }
CaO .30 } Al_{2}O_{3} .34 SiO_{2} 1.48
K_{2}O .20 }
Mix:
White Lead 129
Whiting 30
Spar 111
Calcined Kaolin 22
Kaolin 11
5. Matt glaze.
Cone 7 Formula
CaO .75 } Al_{2}O_{3} .55 SiO_{2} 2.10
K_{2}O .25 }
Mix:
Feldspar 139
Whiting 75
Calcined Kaolin 55
Kaolin 13
For colored glazes add to any of the above:
Blue:
Cobalt Oxide 3 parts
Slate blue:
Cobalt Oxide 3 parts
Nickel Oxide 1 part
Warm blue:
Cobalt Oxide 2 parts
Iron Oxide 1 part
Green:
Copper Oxide 8 parts
Blue green:
Copper Oxide 8 parts
Cobalt Oxide 1 part
Cool green:
Copper Oxide 8 parts
Cobalt Oxide 1 part
Nickel Oxide 2 parts
Olive green:
Copper Oxide 6 parts
Iron Oxide 4 parts
Orange brown:
Iron Oxide 8 parts
Red brown:
Iron Oxide 8 parts
Chrome Oxide 1 part
Zinc Oxide 3 parts
Yellow:
Uranium Oxide 3 parts
The coloring oxides should be weighed out and ground with the glaze. Any
of the colors may be mixed together in order to modify the hue obtained
or the amount of each coloring oxide may be varied to give a stronger or
weaker value.
Opaque tin enamel.
Cone .02 Formula
PbO .40 }
CaO .25 } { SiO_{2} 1.75
K_{2}O .20 } Al_{2}O_{3} .25 { SnO_{2} .30
ZnO .15 }
Mixture:
White Lead 103
Whiting 25
Feldspar 111
Zinc Oxide 12
Kaolin 13
Flint 27
Tin Oxide 45
Grind, with one-half pint of water, for 45 minutes.
PART V: THE DEFECTS OF GLAZES
While it may chance that body and glaze and fire are so adjusted that
faults do not develop, this state of things is rare. Besides, it is
always possible that an occasional trouble may arise, hence it will be
well to recount a few of the commonest defects with the method of cure.
A cure is not necessarily specific. There may be a complication of
causes but the remedy indicates the line along which relief will be
found.
1. Crazing. Fine cracks appear in the glaze but do not penetrate the
body. There are many causes. The body may be underfired or overfired. In
the former case the crazing does not always appear at once and it grows
worse upon standing. In the latter case the glaze is found to be crazed
when taken from the kiln and it does not extend even after long
standing. The glaze may be underfired. In this case the lines of the
crack are broken and irregular, one often changing its direction without
meeting another crack. In all these cases the remedy is obvious.
Crazing also occurs when both body and glaze are correctly fired but
there is an inherent disagreement in expansion. In such a case a little
flint added either to the body or to the glaze will tend to cure the
trouble but it must be remembered that the addition of flint to the
glaze is apt to render it less fusible and therefore while one craze may
be cured another may be caused. The addition of flint to the body is the
simplest remedy.
2. Shivering or peeling. This is the reverse of crazing and is caused by
the glaze being too large for the body. It almost always appears
immediately the ware is cooled. The symptoms are that edges or convex
surfaces are pushed off and even the ware itself is shattered. The
remedy is to decrease the flint in either body or glaze.
3. Blistering. Glazes, both bright and matt, are apt to develop blisters
at times. These may be yet unbroken when the kiln is opened or they may
have melted down to a small crater, a ring with a depression in the
center. The cause of this fault is usually to be found in the body. All
clays contain sulphur and when a clay is aged this develops an acid
which rises to the surface of the ware when dried and causes a scum. The
glaze attacks this sulphate scum and a gas is generated which boils out
and causes the blisters. If old clay blisters and new clay does not it
may be regarded as certain that this is the cause. A little barium
carbonate added to the clay will help to effect a cure. About one per
cent. is usually enough. Clay so treated, however, must not be used in
plaster molds as the barium attacks the plaster. If the cause be not
found in the clay it may exist in the glaze itself. Some glaze
ingredients contain impurities in the form of sulphates and these will
cause blisters.
4. The glaze flows, leaving bare places. It is too fluid, add a little
clay and flint.
5. A matt glaze burns to a bright surface. Matt glazes must be used in a
very thick coat. If too thin they will inevitably brighten. The fire may
be too high. The fire may be "reducing," that is, with insufficient air.
6. The glaze crawls or rolls up in lumps. Notice whether the glaze is
cracked before burning. If so it will surely crawl. Too fine grinding is
usually the cause of this trouble. Too much clay in the glaze may cause
it, or a too porous body. A body which is underfired will almost
certainly cause the glaze to crawl.
7. Pinholes appear in the glaze when cool. Too rapid cooling is the
cause.
PART VI: ALKALINE GLAZES
The glory of the Persian and Egyptian blue is too alluring for potters
to withstand. Though the pursuit of this glory leads one into all kinds
of disasters and failures, the avenues of research that it opens add
unending fascination to the study. Even one beautiful glowing pot out of
twenty or more efforts is a stimulating achievement though it should not
be thought that this is the usual proportion.
It is a continual source of astonishment that with a slight variation of
glaze formula a positive green will swim into a vibrating blue. The
addition or substitution of one substance or another in the glaze mix
may be the key to an unexpected transformation and may give the potter a
new palette of color.
The clay body has a very positive effect on alkaline glaze both in its
composition and its color. This is especially true under a transparent
glaze where the effect is considerable since the color of the glaze
would be modified by the red or buff clay showing through.
If, therefore, the object of the potter is to obtain a brilliant
"Persian" blue, a white clay body must be composed or a white _engobe_
applied over the buff or red clay to hide the color.
The Persians and Egyptians used a coarse, sandy body high in silica and
covered the roughness of the clay with a fine white _engobe_ on which
they painted their decorations in various colors. The whole was finally
covered with the transparent alkaline glaze.
While the effect of colored clay under opaque glaze is less pronounced,
it still makes sufficient difference to be considered.
The word _engobe_ is French and refers to a thin coating of clay, also
called a slip, laid over a colored body to change the color or over a
coarse body to give a finer texture.
The _engobe_ is usually composed of china clay, flint, and feldspar much
as a white earthenware body is constituted but with a larger content of
flint. Ball clay may also be used but the color is not so white.
The mixture of porcelain given on page forty will make an _engobe_
suitable for many clay bodies. If it should crack on drying more flint
should be added.
An _engobe_ must, of course, be put upon the unburned or green clay ware
and this should be leather hard, not dry. The body with the _engobe_ may
be burned before glazing or the glaze may be put upon the unburned ware
and the whole subjected to one fire only.
The ingredients in alkaline glazes are soda-ash, whiting, feldspar,
flint and oxide of tin. The following is an example of a fritted glaze:
Na_{2}O .60 }
K_{2}O .10 } Al_{2}O_{3} .10 SiO_{2} 1.30
CaO .30 }
Soda Ash 64
Whiting 30
Feldspar 56
Flint 42
The entire batch is fritted and ground in a ball mill with the usual
amount of water for fritt grinding, adding a tablespoonful of gum
tragacanth mucilage to the batch after it is sieved. The glaze should be
the consistency of heavy cream when used.
It is also possible to use an alkaline glaze in the raw or unfritted
state. This necessitates grinding by hand in a mortar, but great care
must be taken to mix the dry ingredients thoroughly before adding water
and to stir the glaze constantly while pouring in the water, otherwise
the soda-ash will cake and harden and be very difficult to break up. A
batch of glaze can be ground by hand in fifteen or twenty minutes if
done vigorously. It is then put through a 120-mesh sieve. The
consistency is of importance. If too much water has been added and the
glaze has become thin, it cannot be used successfully and should be
discarded. Unfritted alkaline glaze does not keep well when moist but
the ingredients can be ground dry and kept ready to be moistened as
needed.
The following is an example of an unfritted alkaline glaze:
Na_{2}O .59 }
CaO .21 } Al_{2}O_{3} .20 SiO_{2} 1.6
K_{2}O .20 }
Soda Ash 62
Whiting 21
Feldspar 111
Flint 24
For color add the following oxides to a batch.
1. Egyptian blue, opaque--from 5 to 8 grams of black oxide of
copper--16 grams of oxide of tin.
2. Persian blue, opaque--from 8 to 10 grams of black oxide of
copper--16 grams of oxide of tin.
3. Sapphire blue--1 gram black oxide of cobalt.
4. Aubergine--9 grams black oxide of manganese.
The clear glaze without any coloring oxide can be used over any of the
colored glazes. This is sometimes necessary when the colored glaze
contains such a large proportion of coloring oxide as to show black on
the surface.
The application of alkaline glaze is very important. Any of the three
methods of pouring, dipping, and brushing can be employed. Brushing
seems to give the best results but the glaze must be put on thick, in
two or three coats, to give quality.
The firing is interesting and important because of the varied effects it
develops from the same formula. The range of temperature is great,
varying from cone .05 to 1, developing the alkaline glaze according to
the result desired. If the biscuit is soft fired the color will be more
intense; if hard fired, the color will be much lighter in value with a
high sheen on the surface. An unfritted alkaline glaze burned to .05
develops a soft matt finish.
Where the color of a transparent Persian blue comes out olive green, too
little glaze has been used on the piece or the buff of the clay has
modified the color. Bubbles mean undeveloped glaze or sulphur in the
clay or fuel. Black scum shows an excess of copper in the batch, or
reduction in the fire. Sand paper surface proves too low firing or too
thin a glaze.
If one desires to reproduce the underglaze Persian decoration the black
outlines may be drawn with a black underglaze color mixed with clay. A
little mucilage must be added to secure smooth working. The turquoise
blue is copper oxide, the dark blue cobalt, and the purple manganese.
The oxides must be diluted with white clay and used rather thin. The
Rhodian red is a finely ground red burning clay mixed with a little
flint. This red must be laid on quite thickly. It will probably be found
necessary to fire the painted decoration to about cone .03 before
glazing. The glaze may be either quite clear or slightly tinted. Another
effect may be produced by using the black outline alone under a peacock
blue or turquoise glaze.
A great many modifications and additions to this subject will suggest
themselves to the potter as he works, and a continual study of the
masterpieces of the Persians in the museums will prove the greatest
inspiration.
CHAPTER XVI: DECORATION
The necessity for some kind of decoration upon the clay will always be a
point of difference amongst artists. Some prefer the simple form with a
glaze treatment only, others consider that the surface should be broken
up by design. The question will not be debated here. The aim of this
hand-book is instruction and the individuality of the worker is to be
encouraged. Directions for executing the different treatments do not
imply that these elaborations are advocated. That must be left to the
inspiration of the worker.
Decorations may be applied upon the soft clay by incising, inlaying and
embossing; upon the dry clay or upon the burned pottery in color under
the glaze or with no glaze at all; in the glaze by the use of colors or
colored glazes; or over the glaze with colors and enamels. Each of these
methods possesses special features. Each has its own possibilities and
limitations and these should be mastered by the craftsman.
As in the production of form a well-planned design should be prepared.
The first sketch should be made on paper or on a slab of clay but the
fitting and final arrangement are best made on the piece itself.
Incising consists in the excavation of a shallow trench or trough on the
surface of the clay. The vase or jar having been finished should be kept
in a damp place so that the clay does not dry out completely. The design
may be made in India ink with a brush. A steel tool with a narrow chisel
end is used for cutting and care must be taken that the clay is in such
a condition of moisture as will admit of a clean trench being dug
without any rough or broken edges. The bottom of the trench need not be
very smooth but the edges should be sharp and the lines well defined. At
the same time a mechanical hardness of finish is to be avoided. The
plastic nature of the clay should be kept in mind and every surface,
though decided in character, should be soft and expressive. This result
can be secured by working over the cutting with a moist camel-hair
brush. The work must not be mopped so as to leave a woolly effect, but a
little sympathetic penciling will remove the hard lines of the tool.
There are two possible developments of incised work. The details of the
design may be excavated or the background may be cut out leaving the
drawing in relief.
In modeling embossments the piece should be a little softer than for
incising. It is important that in any clay work attached to a clay body
the same amount of moisture should be present in both parts. This is not
entirely possible in modeling upon forms which have already been shaped,
for if the form be as soft as modeling clay it will not bear to be
handled, while if the clay were as hard as the form it could not be
worked. A compromise is therefore necessary. The vase must be kept as
soft as possible consistent with holding its shape and the clay must be
as stiff as the working will allow.
As little water as possible should be used and the modeling should not
be brought to its full height at once. If the clay be laid on little by
little there is much less chance of cracking. Low relief is sometimes
produced by painting in slip but here even more care is necessary. The
slip should be laid on with a brush in thin coats, each coat being
allowed to stiffen before another is applied and the whole work being
kept moist.
An atomizer with clean water is useful in this regard. The work, being
kept on a whirler or turntable, is sprayed now and then with water and
thus prevented from becoming too hard.
When the slip work has been raised to the desired height the surface is
tooled over so as to remove the brush marks. This is the method which
has been brought to such perfection by the French artists and by them
named _pâte-sur-pâte_.
Modeled work is generally carried out in the same clay as that of which
the form is made and depends upon high relief for its effect. Slip
painting is usually done in a different color and if a light-colored
slip be used upon a dark clay, the latter is partially seen through the
coating in the thinnest places. This fact is made use of to accentuate
the shadow effects.
In using one clay over another great care must be taken to insure that
the fire shrinkage is the same. The white body already given, or indeed,
any light colored clay, may be tinted by the addition of under-glaze
colors. The dry color, if sifted very fine, may be added to the plastic
clay by thorough kneading and wedging but it is better to work up the
clay into a slip and to stir in the color. The tinted slip is then
lawned two or three times and dried out on plaster or used in the slip
state as the case may be.
A trial should be made before any important work is undertaken, both to
see that the color is right and to discover any discrepancy in
shrinkage. If a clay shrinks too much, a little ground flint may be
added. If it shrinks too little, a little ball clay will correct it. The
tint produced by the color is apt to darken in the kiln but the general
hue will be similar to that of the color used.
For some classes of work a native red clay gives admirable results. It
may be lightened by the use of kaolin and flint and darkened by adding
burnt umber. These colors are more satisfactory than greens and blues in
clay because the brown and red tones are natural, the others are
artificial.
If a good buff-burning clay be available, it forms the best possible
foundation for color work. Burnt umber will darken it and red clay may
be mixed with it, always having regard to the matter of shrinkage
already mentioned.
Very pleasing effects may be produced by inlaying one clay with another.
The pattern or design is first cut out as described under incising and
then the second clay is pressed, morsel by morsel, into the excavation.
The surface is cleaned off level with the body of the piece and the
whole may be either polished or glazed.
A plastic clay can be polished when leather hard and the finish will
remain after firing. Any tool of steel, boxwood or ivory will do the
work but a good supply of patience is needed so that the whole surface
may be uniformly treated.
For color decoration upon the pottery, ordinary underglaze colors are
used, either upon the unburned clay or upon the burned ware commonly
called biscuit. For use upon the clay, the colors should be mixed in
water, using a little molasses, sugar, glycerine or gum arabic to make
the color flow easily from the brush. Before burning, a little glaze
should be sprayed over the work with an atomizer. Any ordinary fusible
glaze will do. It is diluted with a good deal of water as only the very
thinnest coat is necessary. The spray should not be held long in one
place or the water will flow and smear the color. If the piece be turned
slowly around the clay will absorb the water as it is applied. If this
spraying be not done the colors will be apt to rub off after burning.
Under-glaze colors are not fusible and hence they come from the fire as
dry powders.
The work on the biscuit is much the same except that turpentine and fat
oil constitute a better working medium. When dry the spray should be
applied as before.
CHAPTER XVII: THE FIRE
Kilns and burning form the pivot upon which the art of the potter turns.
M. Doat has said, "A potter can no more express himself without his kiln
than can a violinist without his violin," and yet there are some who try
to make out by sending their work to some nearby pottery to be burned.
Let it be at once understood that he who finds it impossible to procure
and manage a kiln had best take to some other craft.
Kilns are of two types, open and muffle. In the open kiln the flames
pass through the firing chamber and the ware may be exposed to their
action, as in stoneware and brick; or it may be enclosed in the
fire-clay cases, called saggers, as in the many forms of pottery, dishes
or faience. The muffle kiln is a closed chamber which is surrounded by
flames but which is not entered by them. These kilns are used in the
manufacture of terra cotta and heavy enamel wares, and the portable
kilns made for studio use are of this type.
There are certain advantages to be gained in the use of either type of
kiln but inasmuch as the open kiln involves the use of saggers and as,
moreover, it must be properly constructed of fire-brick by a skilled
mason, it will be best to consider only the portable studio kiln.[M]
[M] These kilns are made in several sizes by the H. J. Caulkins
Company, Detroit, Mich.
It must not be expected that any kiln will give perfect satisfaction.
Neither built kiln nor portable kiln will do this, but either may be
relied upon to do excellent work in the hands of those who will take
trouble. A kiln of the proper size having been purchased, it must be
carefully installed. A good chimney is an absolute necessity and if one
can be built on purpose it will be best. It should be at least
twenty-five feet high with the bottom lined with fire-brick to a height
of six or eight feet. The portable kiln is set on iron legs which raise
it about one foot from the floor. This is not enough for easy work and a
platform of brick or stone, ten inches high, should be prepared. This
will greatly simplify the observation and management of the burners
which are beneath the kiln, and if it should make the inside of the
muffle hard to reach, it is easier to stand on a box to attend to the
kiln than it is to go on one's knees to the burner.
The kiln room should have a cement floor and should be both well drained
and well ventilated. At the window there should be a stout bench where
the work of preparation may be done and at a convenient spot there
should be shelves for stilts, cones, wash, stopping and all the minor
accessories of burning. If there is room for a barrel of oil it will be
a convenience, and if the room be fire-proof the insurance company will
not object.
The kiln having arrived it is mounted on the platform and the
asbestos-lined pipe is securely connected with the chimney. The inside
of the muffle is examined with care to see that no part has been jarred
in transit. The reservoir cans are filled with oil and a slow fire is
started. This should be allowed to burn very gently for an hour or two
in order to thoroughly dry out and season the kiln. It is a good plan to
make up a wash of equal parts of kaolin and flint and to brush this all
over the inside of the kiln. It should not be put on so thick as to
shell off from the walls but at the bottom a good coating may be laid.
This protects the walls of the kiln from the attacks of glaze and will
make them last longer.
In order to fill the kiln economically a number of props and bats must
be provided. Some of these are sent out with the kiln but one is always
needing odd sizes and extra pieces. The props are simply legs of burned
clay; they are of any height desired and should be thick enough to stand
alone. The bats are slabs of burned clay and they rest on the props to
form shelves. The bats must be thick enough to bear the weight of any
pieces which they may be called upon to support, but they need not be
very large as two or more may be used to bridge the width and length of
the kiln. Bats and props are best made of sagger clay to which has been
added about one-third of crushed fire-brick. Broken bats serve well for
this after the first supply has been secured. This crushed burned clay,
called grog, has a very important influence upon wares which have to be
heated again and again. The size used should be about what will pass
through a 16-mesh sieve, and if the dust be sifted out through a 48-mesh
sieve, the resulting ware will be stronger. That is, only the grog which
passes a 16 sieve but lies upon a 48 sieve should be used.
The relative proportions of clay and grog in the mix will depend
somewhat upon the nature of the clay. Three parts of clay to two of grog
by measure will be about right.
The first charging of the kiln should be with pieces of no great
importance. The temperature in different parts must be carefully
ascertained. In order to do this a number of pyrometric cones[N] are
prepared in groups of three.
[N] The pyrometric cones are fusible pyramids for testing heat. They
are made by Prof. Edward Orton, Jr., Columbus, Ohio.
Let us suppose that the work is intended to be carried out at a
temperature of Cone No. 01. The numbers run both ways from this. The
higher or less fusible cones are, 1, 2, 3, 4, etc., up to 36, and the
more fusible numbers are 02, 03, etc., down to 022. If the firing is to
be to Cone 01, numbers 02, 01 and 1 are selected and set upright in a
small strip of soft clay. Eight or ten of these groups of three cones
are to be prepared for the first firing, so as to test the kiln, one
group is placed in each corner, at the bottom, and another in each
corner on a shelf, which is arranged opposite the spy-hole in the door.
In the middle of this, where it can be well seen through the hole, one
of the groups of cones is placed. They must be set so that all three
cones are visible as the kiln is being fired.
The kiln is now filled up on both levels with pieces of pottery. To burn
an empty kiln is not a reliable test. On the first occasion the fire
should be started in the morning because no one can tell just how long
the burn will take. When this time is ascertained it is best to start
the fire so that the kiln will be finished by early evening. The cooling
then takes place at night and there is no temptation to open the door
too soon.
The fire is started slowly and the flow of oil is gradually increased as
the muffle begins to glow. The work here needs practice, nerve and
judgment. A good deal of smoke will be seen at the chimney at first but
this should disappear as the kiln grows red. If the fire be urged too
strongly at the beginning fuel will be consumed to no purpose, the only
result being the choking of the flues with carbon. As the red becomes
visible through the spy-hole, more oil may be supplied, but notice must
be taken that the smoke at the chimney does not increase. The ideal
firing is where there is no smoke but this cannot be reached until the
kiln is hot enough to cause the smoke to burn.
Persons who have burned kilns for overglaze work will find the method of
burning pottery very different. Instead of a fire brought as rapidly as
possible to the finishing point, there must now be a slow soaking burn
in which the heat shall have time to saturate the ware.
The cones in front of the spy-hole must be observed from time to time
and presently as the kiln reaches a bright cherry red, number 02 will
begin to bend at the tip and will gradually arch over until the point
touches the shelf upon which the cones stand. By this time number 01
will have begun to bend and when the point of this has touched the
shelf, the firing is over and the oil is shut off.
It requires some resolution to leave a kiln until morning but it is
conducive to early rising anyway. The kiln need not be quite cold but it
will help the kiln itself to wear better and the pottery will be better
if nothing is done until everything can be handled without gloves.
The cones are now taken out and a diagram is made of each level with the
bend of each cone accurately drawn. This diagram should be mounted and
hung on the wall for reference. It is not well to trust to memory. It
will probably be found, in the type of kiln we are discussing, that the
cones on the bottom have bent further than those on the shelf. That is,
the bottom is somewhat the hotter.
The variation in the kiln is not necessarily a disadvantage. It may be
utilized in burning wares of different kinds. For example, if the bottom
prove much the hotter, the biscuit ware may be placed below and the
glazed pieces on the shelf. In such case the shelf itself should be
washed with a good coating of clay and flint in order to protect it from
casual drops of glaze.
If a number of small pieces are being made, more than one shelf should
be set up. The legs may be just a little taller than the tallest of the
small pieces, but the art of placing or filling a kiln economically
consists in making selection of pieces which fit well together both as
regards height and shape. Thus, pieces which are large at the base may
be dovetailed in with others of which the base is smaller than the upper
part. In the case of clay ware the pieces may be set close together or
even piled one upon another. There is no danger of sticking unless the
ware is burned to complete vitrification. The glazed pieces must not, of
course, touch each other.
It will be seen, from these instructions, that there should be a good
assortment of wares from which to select. Economical firing cannot be
managed if a burn be attempted whenever a piece is ready, and patience
must be exercised so as to fill the kiln to advantage.
It is important that anyone attempting to burn a kiln should have some
understanding of the phenomena of combustion. Many things occur in the
firing which, without such an understanding, are not easily explained
but which become perfectly clear when considered in the light of simple
chemical science.
Combustion means oxidation or a combination between the elements of the
fuel, principally carbon and hydrogen, and the oxygen of the air. This
combination is a chemical action and as it proceeds heat is liberated.
With a given amount of a specific fuel and a given amount of air there
is always the same amount of heat, but the rate at which this heat is
given off varies with the time occupied in the operation. Heat may be
generated slowly which means a low temperature, or the same volume of
heat may be generated rapidly, occupying a much shorter time and
developing a higher temperature. From these statements it will be seen
that there is a difference between heat and temperature; heat means
volume, temperature means intensity. Thus the temperature derivable from
a given amount of fuel depends upon the rapidity with which it is
burned.
Combustion may be either complete or incomplete. In the former case
enough air is supplied to oxidize all the fuel with, usually, some
excess. The contents of the kiln are then bathed in the heated oxygen
and the condition of the burning is called oxidizing. When the
combustion is incomplete, on the other hand, there is a deficiency of
oxygen. The kiln is charged with hot carbonaceous gases and smoke, and
these, being hungry for oxygen, will abstract it from any substance
which may be present. This condition is called reducing because the
compounds which exist in clay or glaze are deprived of oxygen and thus
reduced to a lower state of oxidation.
In burning a kiln one should be able to produce either of these
conditions at will because there are certain wares which require one or
the other in order to secure the best results. To put the matter in a
nutshell, oxidizing conditions are induced by a strong draft and open
flues, reducing conditions are obtained by closing the air inlets and
using a liberal amount of fuel.
CHAPTER XVIII: HIGH-TEMPERATURE WARES
The subject of "Grand Feu Ceramics" has been so ably developed by M.
Taxile Doat in his admirable treatise[P] that it will be unnecessary to
go deeply into the matter, but in order that the reader may be aware of
what is involved, some description of the technique will be given.
[P] Keramic Studio Publishing Co., Syracuse, N. Y.
Hard-fired wares are divided into two classes, porcelain and stoneware.
The latter is called by the French, "Grès," an abbreviation of the name
"Grès de Flandres," the stoneware made in the low countries in the
sixteenth century. Both these wares are, technically, once fired, that
is, the body and glaze come to maturity at one and the same burning. The
biscuit ware is often given a low burn at first in order to facilitate
handling, but this leaves the body very porous and is in no sense a
maturing fire. The glaze is laid upon this porous ware, or upon the
unburned clay if preferred, and then comes the high fire or "Grand Feu"
of the French.
A mix for a porcelain body has already been given but if the ceramist
means seriously to attack the porcelain problem he will have to do some
experimental work for himself. The Georgia kaolin mentioned in the
recipe on page 40 is a good, plastic clay but it is slightly off color.
It may be necessary to improve the color by the use, in part, of another
kaolin such as the Harris clay from North Carolina.[Q]
[Q] The Harris Kaolin Company, Dillsboro, N. C.
Furthermore, in the preparation of a fine porcelain it is necessary to
grind the whole mix upon a mill. The mill used for glaze grinding will
answer every purpose and care must be taken that the grinding, while
carried far enough, be not too long continued. A certain amount of fine
grit in the body mass is necessary but only by constant practice can the
right point be reached. In making these experiments each step should be
faithfully noted in a handy book. The amount of water to a given weight
of clay and the duration of the grinding should be accurately observed
and written down. It is most unwise to trust to memory.
The process of casting may be used for porcelain as already described,
but the very best of workmanship is necessary. The hard fire to which
the porcelain is subjected reveals every error which has occurred in the
making. The same thing applies to wheel work. Not only is great skill
required in order to shape the tender porcelain clay on the wheel but
the very essence of the porcelain is its lightness, to produce which by
craftsmanship a long and arduous course of training must be endured.
Stoneware is free from many of these difficulties and, consequently one
who attempts the conquest of high-temperature wares is advised to begin
with this. Stoneware clay need not be a mixture. There are many clays
which can be used for the manufacture of grès with no more preparation
than that laid down for common clays.[R] It sometimes happens that a
clay will need the addition of a small quantity of flint or spar but
this does not amount to a difficulty.
[R] Stoneware clays may be procured from The Western Stoneware Company,
Monmouth, Ill.; H. C. Perrine and Sons, South Amboy, N. J.
Stoneware does not present the same manufacturing difficulties as are
found in porcelain. The clay is quite plastic and can be easily shaped
on the wheel; casting is scarcely a suitable process for this ware. The
essence of stoneware is strength and virility, just as that of porcelain
is lightness and grace. Each ware has forms suited to itself and it is a
mistake to depart from these essential characteristics.
After shaping and drying the technical manipulation of both wares
proceeds along the usual lines. The first fire is at a very low
temperature. The melting point of silver (cone 010) is enough in nearly
every case. This leaves the ware in a soft and porous condition but hard
enough to resist the action of water. The process of glazing has already
been described but the composition of the proper glazes differs from
that of low temperature glazes.
Porcelain is always burned in a reducing fire; stoneware may be burned
either reducing or oxidizing. The temperature at which the glaze is
burned is very high, it must be, in fact, the maturing point of the body
itself.
The simplest form of porcelain glaze is that represented by the formula--
K_{2}O .3 }
CaO .7 } Al_{2}O_{3} .5 SiO_{2} 4.0
Which is carried out in the following mixture:
Feldspar 167
Whiting 70
Kaolin 52
Flint 108
----
The glaze is ground for use.
The same glaze will also serve for stoneware but it will burn to a
brilliant surface whereas stoneware is better when finished with a matt
texture.
The following is a stoneware matt glaze:
K_{2}O .3 }
CaO .7 } Al_{2}O_{3} .7 SiO_{2} 2.6
Of which formula the mixture is--
Feldspar 167
Whiting 70
Calcined Kaolin 66
Raw Kaolin 26
----
The porcelain glaze is at its best when uncolored. The matt glaze will
be more interesting when used as a colored coating.
The following are a few suggestions for colored matt stoneware glazes.
To the glaze batch, 329 parts, add:
For blue:
Cobalt Oxide 2 parts
Nickel Oxide 1 part
Ground Rutile 10 parts
For brown:
Iron Oxide 6 parts
Nickel Oxide 3 parts
Ground Rutile 10 parts
For green:
Chrome Oxide 2 parts
Cobalt Oxide 1 part
Iron Oxide 4 parts
For dark red:
Iron Oxide 10 parts
Chrome Oxide 2 parts
Zinc Oxide 6 parts
Rutile has not before been mentioned. It is a crude oxide of titanium
and is exceedingly useful in high temperature work for producing odd,
mossy and crystalline effects.
These mixtures make no pretense to be complete, they are given as
suggestions only because if the artist-potter is to be successful he
must be prepared to compound glazes which are the expression of his own
individuality.
For burning high-temperature wares the kilns already described may be
used but upon purchasing it should be stipulated that the kiln is to
stand burning up to cone 11 or 12. Successful porcelain can be made at
cone 10 but better results are secured at cone 12, though, of course,
the wear upon the kiln is proportionately greater. Stoneware requires a
burn of about cone 9, higher or lower according to the clay used but
fine results must not be expected below cone 7 nor is it necessary to go
higher than cone 10.
CHAPTER XIX: CLAY-WORKING FOR CHILDREN
One of the modern developments of clay-working is the use of it in
elementary and high schools as a branch of manual training. In this,
clay meets the most exacting needs of the work for it affords a perfect
means of self-expression. Other arts interpose between the pupil and his
material a series of tools or appliances, more or less elaborate, which
constitute a barrier to the personal touch. Clay presents no such
obstacles. The ten fingers are all the tools that are necessary at the
beginning and, consequently, the personal equation in clay-working is
remarkably high.
In the kindergarten the children take to clay work as little ducks to
water and the interest is never lost. In this way, clay, instead of
adding to the labors of a teacher already overburdened by a plethora of
subjects, constitutes a real relief. The work is so interesting that it
moves along of itself and all that is needed is intelligent direction.
It is, of course, necessary that anyone attempting to teach clay-working
to children should have a knowledge of methods and principles. The
essence of power, especially in teaching, is reserve, but there is great
danger in expecting too much from small heads and hands. In the early
exercises the skill of the teacher should even be employed to conceal
her art. It is a mistake to place before elementary pupils work which is
far beyond their reach. Let the teacher make before the class something
which they themselves can do if they try and they will be encouraged to
greater effort.
A small cylinder is a suitable beginning exercise for several reasons.
The form is definite and the result may therefore be easily criticized
by the children themselves, the size of the piece may be readily adapted
to the small fingers and the simplicity of line enables the attention to
be concentrated upon the manipulation of the clay.
This cylindrical form may be made more interesting by the addition of
little feet or handles; by a simple line border incised along the upper
edge; or by dividing the surface into well-spaced panels. The planning
of the cylinder itself is a good exercise in rectangle proportion.
In order to enable the pupils to turn their work from side to side each
one should be provided with a piece of paper or cardboard the size of
the base of the pottery. The building is started upon this and, managed
in such a way, the clay does not stick to the table.
When the idea of pottery building, either by coils or by pieces welded
together, has been grasped, the children should be taught to think in
the solid. There is almost always a difficulty in making children see
that an outline drawing and a solid form may be alike in meaning. The
teacher should draw upon the blackboard a simple jar in elevation, the
plan, of course, will be a circle. The same thing is then made in clay
by both teacher and children and the results are compared with the
drawing. This will lead to the designing of the forms in outline by the
children themselves. These designs should be made the exact size of the
proposed pottery and if the outline be carefully cut out the line of the
paper may be applied to the work as a template. By such means the
children are led to produce accurate lines in the clay and control over
the material is secured.
There is always a temptation, when the clay sags or loses shape, to
diverge from the original idea and to allow the material to shape
itself. This inevitably leads to slovenly work and should be resisted
from the first. The paper template helps to correct such an impulse and
the pupil presently finds that the clay can be successfully controlled
if enough trouble be taken. There is much interest too in the cutting of
pottery forms from folded paper. A number of these forms may be pinned
on a screen and the children led to select the best in line and
proportion. Too much emphasis cannot be laid on the necessity for
showing the children fine examples of pottery, both ancient and modern.
The more primitive types, where the form and the decoration are so
perfectly adapted to each other and to the material, are full of
inspiration for the child potter as well as for the adult. When one is
fortunate enough to be near a museum, many illustrations will be found,
but good photographs or drawings are available for almost everyone.
Constant comparison and the exercise of choice will lead to a
development of taste, which must affect the child whether he later
becomes a producer or a consumer.
A flower holder is a good problem. It is a solid piece of clay two or
three inches in diameter and an inch thick. This may be round or square
in form and may have simple modeled decoration added to it. Quarter inch
holes are pierced at regular intervals, in fact, they themselves should
form part of the design. For the older children a shallow bowl of good
line with a flower holder to fit is an interesting problem. Other good
problems, which may be made more or less difficult according to the
grade in which they are given, are rose jars, bread and milk bowls,
incense burners, cylindrical jars, square fern dishes, candlesticks and
small lamp bases.
When working out decoration for pottery forms, it is well to have the
children make their designs with the modeling tool upon the clay itself.
If a piece of soft clay be rolled out flat upon the table it affords the
best possible medium for making clay designs. The pupil is at once put
in touch with the possibilities and limitations of the material. A
drawing made upon paper may have to be entirely changed before it is
suitable for use on clay. The soft surface can be smoothed over as often
as necessary and a new sketch made until a design is approved for
application to the pottery itself. In the chapter on decoration will be
found suggestions for clay treatment.
The making of tiles affords an interesting application of the principles
of design, but the instructions in the chapter on tile should be
followed in order to insure a workman-like product. If it is possible to
use plaster, the making of a decorated tile from which a mold can be
made and other tiles pressed is a good problem. Animal forms lend
themselves to the decoration of such tiles and are always interesting to
children.
While these chapters are especially devoted to ceramics in the sense of
burned and glazed pottery a few words upon modeling as related to school
work may be added here. Imitative modeling from cast or copy with its
development of animal and figure modeling, both from life and from
memory, is valuable in the acquirement of the power of manipulation and
control as well as in the cultivation of observation, imagination and
memory. In the best regulated schools the work of the grades is often
correlated in the study of some phase of human life. Facts are grouped
around some epoch or event in history or some country or clime in
geography. The children take up the clay while their minds are full of
the current subject and nothing more natural than that they should
illustrate the story by models.
Such work is to be thoroughly commended as truly educational, though it
does not fall strictly within the field of pottery and a few suggestions
may therefore be in order.
The modeling of animals or people for the sand table is full of interest
for the younger children. Such stories as "The Three Bears," "Chicken
Little" and "The Little Red Hen" immediately suggest themselves. For
children of about the fourth grade "Alice in Wonderland" offers a most
fascinating array of models. "The White Rabbit," "The Duchess," "The
Mock Turtle," "The Mad Hatter," grotesques of all sorts, seem a natural
outcome of this illustration work and the wise teacher will see the
possibility for developing the imagination in the modeling of mythical
creatures, such as dragons and gnomes, and in the personification of the
elements. There is also an unlimited fund of material in the tales of
knighthood and of fairyland.
With the older children, simple principles of design and composition
should be suggested. A paper weight is an interesting problem demanding
the adaptation of form to space.
Many of these things may be modeled in clay, dried and painted with
water color or one of the patent modeling clays which set like cement
may be used. If no supports have been left in the model it may be fired
when thoroughly dry.
Some of the best projects for sand table work involving modeling are
Eskimo Life, Indian Life, Farm Life, The Circus, and Fairy Tales.
Generally a suggestion is all that is necessary to call forth the most
original conceptions and once started the children will soon far
outstrip the teacher.
INDEX
A
Alhambra Vase, 16
Armenian Bole, 15
B
Ball-Clay, Tennessee, 40
Bases for Glaze, 143
Berlin Porcelain, 28
Bisilicate Glaze, 145, 146
Black Surfaced Ware, 13
Blistering of Glazes, 166
Building, Clay for, 69
Building, Faults in, 72
Building, Methods of, 70, 71
Built Pottery, 10, 68
Burning Tiles, 139
C
Case for Mold-making, 58
Casting, 129
Casting, Slip for, 129
Castor Ware, 13
Children, Pottery for, 194
Chinese Porcelain, 23
Clay, Colored, 36
Clay, Crude, 9, 37
Clay, Decoration in, 173
Clay, for Building, 69
Clay, for Tiles, 134
Clay, Preparation of, 37
Colored Glazes, 24, 143, 163
Colors, Underglaze, 25, 143, 177
Combustion, 186, 187
Cones, Pyrometric, 182
Copenhagen Porcelain, 27
Crawling of Glazes, 166
Crazing of Glazes, 165
Cups and Saucers, 124
D
Decoration, 173
Decoration of Tiles, 137
Defects of Glazes, 164
Devitrification, 152
E
Earthenware, Mixture for, 40
Engobe Ware, Oriental, 15
F
Famille Rose, 24, 26
Famille Verte, 24, 26
Feet for Vases, 105
Firing the Kiln, 179
Fitness in Design, 3, 4, 7
Flowing of Glazes, 145, 166
Form and Weight, 7
Fritt for Glaze, 158
Fritting Furnace, 159
G
Glaze, Bases for, 148
Glaze, Bisilicate, 144, 145
Glaze, Calculation of, 150
Glaze, Fritt for, 158
Glaze, Pinholes in, 167
Glaze, Porcelain, 191
Glaze, Recipes, 160
Glaze, Stoneware, 191, 192
Glazes, Blistering of, 166
Glazes, Clear, 141, 161
Glazes, Colored, 143, 163, 192
Glazes, Crawling of, 166
Glazes, Crazing of, 165
Glazes, Defects of, 164
Glazes, Flowing of, 145, 166
Glazes, Grinding, 151, 155
Glazes, Ingredients for, 142, 143
Glazes, Matt, 152, 191
Glazes, Nature of, 141
Glazing, 140
Glazing Tiles, 137, 138
Grès de Flandres, 21
Gum Tragacanth, 156
H
Hard Porcelain, 23, 189
High-temperature Wares, 188
I
Ingredients for Glazes, 142, 143
J
Jars for Storing Clay, 41
K
Kiln, Firing the, 179
Kiln, Portable, 180
Kilns, 179
L
Lawns, Silk, 41
Large Pieces, 107
M
Matt Glazes, 152
Methods of Making Tiles, 135, 136
Molds for Plates, 62, 63
Molds for Vases, 52
O
Oriental Engobe Ware, 15
Ox-blood Red, 24, 26
Oxidizing Fire, 187
Oxygen Ratio, 145
P
Pâte-sur-pâte, 14, 175
Pieces, Large, 107
Pinholes in Glaze, 167
Plaster-of-Paris, 45
Plaster Dishes, 46, 47
Plaster Head for Wheel, 65, 78
Plaster, Setting of, 45
Porcelain, Berlin, 28
Porcelain, Copenhagen, 27
Porcelain Glaze, 191
Porcelain, Hard, 23, 189
Porcelain, Mixture for, 40
Porcelain, Sevres, 25
Potter's Wheel, 74
Pottery, Built, 9, 68
Pottery, for Children, 194
Pottery, White-coated, 14, 168
Props and Bats for Kiln, 182
Pyrometric Cones, 182
R
Recipes for Glazes, 160
Reducing Fire, 187
S
Salt-glazing, 21
Saucers, Cups and, 124
Shivering of Glazes, 165
Size, Mold-makers', 44
Slip, 38, 39, 129
Slip for Casting, 129
Slip-painting, 175
Stoneware, 21, 188, 190
Stoneware Glaze, 191
T
Tennessee Ball-clay, 40
Tiles, 133
Tiles, Burning of, 139
Tiles, Clay for, 134
Tiles, Decoration of, 137
Tiles, Glazing, 137, 138
Throwing, 77
Tin Enamel, 164
Tragacanth, Gum, 156
Turning Tools, 100
U
Underglaze Colors, 143, 177
V
Vase Forms, Turning, 49-52
Vases, Feet for, 105
Vases, Molds for, 52
W
Weight and Form, 7
White-coated Pottery, 14, 168
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