0VER6LAZE COLORANTS FOR CONE SIX GLAZES

A Paper Presented to the Faculty of the Graduate School University of Minnesota, Duluth

A Requirement for the Degree Master of Arts (Plan B)

By

Ben Levlne University of Minnesota Duluth, Minnesota

June 1968 TABLE OF CONTENTS

CHAPTER

PREFACE iii

I. HISTORICAL

II. RESEARCH INTO 0VER6LAZE COLORANTS

III. CONE SIX GLAZES 10

IV. CONE SIX OVERGLAZE COLORANTS 13

V. RESULTS OF CONE SIX GLAZES AND OVERGLAZE COLORANTS 15

VI. CONCLUSIONS 19

BIBLIOGRAPHY 20 PREFACE

During the spring and sunnner of 1967, as an undergraduate student about to enter graduate school^ the problem of writing a paper and having a graduate exhibit was uppermost in my mind6

Looking back to my undergraduate studies in ceramics I found it had been quite rewarding and I was not as satisfied with the challenge of decoration. In a truly authentic statement is a challenge.

To meet this challenge and develop the creative insights needed^ I embarked upon a series of experiments using ceramic coloring oxides.

The ceramic colorants were to be used as decorative elements to enhance a particular form.

Too often9 testing» experimentation, and the various processes of surface involvement have become ends in themselves. Pottery, instead of being expressive, or fitted for its purpose, has been merely the vehicle for a display of dexterity and technique. The artist potter is constantly searching and exploring for new ideas and ways to perpetuate his existence.

In this paper I have tried to present a useful exposition of the materials and methods which are available to the studio potter in the development of ceramic colorants to be used as overglaze decorations on pottery.

This study has revealed many exciting discoveries that perhaps are known to many. Those of us who have found this direction know that the resolvement of a problem is one of the most important factors in man's existence. Iv I wish to express my gratitude to Professor Gleim C. Nelson9 my ceramics instructor9 for his consideration in making possible the opportunity for graduate study. Also to Dr. Arthur E. Smith9 head of the Department of Art9 for his continued encouragement. CHAPTER I

HISTORICAL

The origins of ceramic colorants are somewhat vague but new historical facts are being discovered every day* These facts are being authenticated by new excavations*

n?om the very beginning of time ceramic coloring oxides were shrouded by mystic legends as was the ceramic ware* The pottery found in the Neolithic settlements of Egj/pt bears geometric ornamentations which were incised and filled in with white paste* White paste filling was expressive to an otherwise lackluster ceramic ware. It added a new dimension in decoration* The Eg3rptians were believed to be the first to have made glazed ware and possibly the first to use metallic coloring oxide* Finds fpcm the Stone and Copper Age (Chalcolithlc Period), made predominantly in Upper Egypt, are known as the Badarian culture, after the chief site. Badari. in Upper Egypt*

The Badarian culture is characterized by burnished red clay vessels which had an abundance of red iron oxide in the clay body* There were no kilns, as we know today, in existence then* Host of the ceramic ware was believed to have been fired in an open field* Turned over and fired on its brim', the lower part of the vase became black, as the ashes from the wood and brush settled at the bottom* The carbonous gases re leased changed the red iron oxide in the clay body to black iron* The burnishing of the rim gave contrast to the warm red clay body*

It is only natural, because of the geographical proximity, that the Nagoda II culture should e9q}and upon the pottery developed in Badari* 2

Nagoda II oulturey whloh originated from Lower Egypt9 modeled clay

•easels from a yellowlsh-grey or reddlah-brown unbumlahed clay. They were painted In a brilliant red» using clay bearing a high concentration of copper. The use of oxides for decoration and ornamentation on clay vessels declined after the Nagoda II culture. Ceramic ware was being used for everyday purposes at this time.

The New Kingdom craft products, which preceded the Nagoda II culture In Egypt, are of particular opulence and variety. The rich treasure of Tutankhamun revealed red clay vessels decorated with orna mental blue bands and festoons and bowls painted with a clay slip bearing cobalt oxide. In a turquoise shade featuring flowers and fish.

Although Egyptian potters appeared very early historically, they never achieved the skill of their contemporaries In Crete. Most of the

Neolithic pottery of Crete Is grey, greyish-brown, or black and burnished.

In the later phases, there are some that are Incised, the lines filled In with white and red clay bearing oxides. Vase painting with oxides In white, red and orange on a chocolate colored ground was In abundance about 1500 B.C.

Slgnlflcaut specimens of vases with sea and floral motifs that were of the swirling and curving types have been found. After the 16th Century B.C. the vessels were painted predominantly In dark colors on a light ground.

The development of the Protocorlnthlan style during the 7th Century

B.C. reflected a strong sense of polychroira effects. The Islands In the

Aegaen produced a variety of Orientalizing styles. The use of a great variety 3 of colors and decorations were adopted :^om the Near East* The great number of oxide beting slips used reflected the ingenious development of stained potteryc

The gradual shifting of importance and influences i^m Athens to Corinth, then Corinth to Athens from 900 B.C. to 600 B.C. was not without its rewards. The development of the Black Figure Ware and the

Red Figure Ware styles confirms the anxieties of the previous periods.

"Black Figure is the name of a technique. By Black Figure one singly means a solid black figure elaborated and enlivened in two ways:

First, by details engraved with a sharp point, incised; and, second, by occasional additions of dark red and white paint. One of the chief uses of white is for female flesh. This gives a sober scheme of four colors: the orange of the ground, the lustrous black of the glaze paint, the white, the deep cherry or crimson, or sometimes purplish red."^ The black gl€use paint was halfway between a glaze and a slip. "The colors were made of an alkaline flux with earth oxides combined with the same clay as used for the -ware.The glazes used are historically significant. They were simple in composition, probably made up of soda ash, sand, and a little clay for adhesion. The lustrous black of the glaze paint for Black Figure

Ware was very similar in composition. It was prepared by making a colloidal

D. Beazley, Development of Attic Black Figure, (University of California Press, 1951), Introduction ^Warren E. Cox, The Book of Po-ttery and , (Crown Publishers, Seventh Printing, January 1940, N. Y.), p. 251 4 suspension of red clay by adding potash to the mixture of clay and water. The finest particles^ rich in iron, were deflocculated and skimmed off the surface. When this was thickened by evaporation it was used as the black glaze. No coloring agents were added to the glaze. The glaze was then applied to the clay body of the vase. "The firing consisted of three phases. In the first, an oxidizing phase, air was firaely admitted to the kiln. If the firing was stopped at that point both the vase and the glaze would emerge red in color. The firing continued, however, with a reducing phase in which there was incon^lete combustion of green wood in the bximing chamber, and the kiln was sealed to outside air. If the kiln was allowed to cool during this phase the vase would emerge an unattractive grey with a black glaze. The firing was concluded with a reoxidizing phase; air was permitted to enter the kiln freely, and the oxygen easily penetrated the porous body of the vase, reoxidizing the black ferrous oxide in the clay to the red ferric form.

The black glaze matter, which also had become black ferrous oxide, was so fine in texture that the heat had sintered and sealed its surface. There fore , the oxygen in the air in the reoxidizing phase could not enter the black glaze, so it remained black. The kiln was allowed to cool and the finished vase emerged with the porous clay a bright terracotta red color and the impervious glaze a jet black..

The Black Figure technique may seem very unrealistic but so is the outline drawing. If the Greek painter had painted in outline on his orange ground, the effect would have been meager and the strong color

^Joseph V. Noble, Ceramics Monthly, (<^175 N« Hight St., Columbus, Ohio, December 1965), p. 19 5 of the background would have eaten up the thin line. The Black Figure technique gave contrast and proper balance of light and dark.

Black Figure was invented in Corinth. Red details were later added. The Black Figure attained its full development in the last decade of the 7th Century. Its influence was undisputed until the invention of

Red Figure technique only 100 years later.

A characteristic of the Red Figure Ware is that the figures,

instead of being painted in lustrous black on the light ground, are reserved, left in the natural color of the clay (white in Corinth), while the background is filled in with black. "Sometimes a yellow or

brown color was added. These colors were made of an alkaline flux mixed with iron earths and were half way between a glaze and a slip."**

The works of the Red Figure introduced shading and brush strokes.

New discoveries in anatomy by Psiax, Euphronies and Euth3rmides led to the

rise of white ground on vase painting. The systematic study of light and shade by Appolodoros and the encaustic technique by Apelles were just a few of the many discoveries during the period. The greatest works in vase painting were culminated in the styles of Red and Black Figure Ware. Many of the techniques and discoveries made then are still ]^ing used today. The incised slip ware of the so-called "Gabri-Type" is of Islamic origin. It was so-called because its enthusiastic discoveries believed it

to have been made by the fire-worshipping Pre-Islamic peoples before 633.

It is now agreed that most of these wares are actually of the 8th to 10th

'^Warren E. Cox, The Book of Pottery and Porcelain, (Crown Publishers, Seventh Printing, New York, January 19*l0), p. 302 6 Centuries. The body of these wares Is actually reddish and they are coated with a white slip over which is a yellowish or green transparent lead glaze sometimes given green, yellow or purplish areas. Later excavations revealed that an ocherous red was added with very rare exam ples of white painted on a ground of black slip.

Lusterware is potteiy that has a brightly shining metallic over- glaze that has become irridescent. That art of luster-painting was believed to have arisen in Mesopotamia and then spread to Syria and

Egypt and west to North Africa and Spain around the 9th Century. The decorative modeled and pictorial designs inherent on most lusterware were modified to the general forms and aid rather than detract from them.

The use of metallic oxides sometimes combined with the glazes and slips gave the artist potter an unlimited palette.

"Faience, the term meaning tin enameled earthenware, or earthen ware covered with a lead-tin glaze was coined in Faenza, Italy. Faenza was an Italian pottery center during the Renaissance. The term was accept ed in France in 1574 when a factoxy was started at Lyons. It is 8ynon3nQous with "majolica.Majolica ware derived its name from ware that original ly came from Spain and the island of Majorca which lay on the trade route to Italy. Faience then was an imitation of Spanish majolica ware.

Faience, or majolica, is actually a kind of glaze-on-glaze painting, often with a later luster decoration. The decoration is on a raw glaze surface. The ware is first covered over with a background

^Warren E. Cox, The Book of Pottery and Porcelain, (Crown Publishers, Seventh Printing, New York, January 1940), p. 354 7

glaze which is to form the base or background for the decoration. The

glaze is usually white, or light in color, and is always opaque. Over this glaze coating the decoration is applied with thin colorants like

a water color paint. When fired, the decoration melts into and fuses with the background glaze. Son» other base glaze may be used which

has been tested and found not to crawl when applied over the background glaze. The detailed masterpieces of Renaissance majolica painting often had several firings. The second and successive firings would req;uire a

flux and a binder. This allowed for freer brush work without disturbing

the .

The history of oriental ceramic decoration is quite extensive.

The most exciting factor to be noted in the freedom and spontaneity

with which the decoration is applied. The most fertile and vigorous makers of symbolic patterns in Japan would go out into natiire to procure

their decorative motifs. They were looking for simple forms in birds,

clouds, leaves or flowers which could be seized upon with a few swift

brush strokes or lines, inlay, slip>trail, or sgraffito. Many of the

drawings were modified for each individual pot. They sought to capture

some small significant portion of the beauty of nature.

"Many primitive patterns look as if they were completely abstract,

but most traditional patterns have a descriptive, literary or some 83rmbolic

origin. The works expressed by primitive and Eastern artists somewhat counteracts the aridity of extx»eii» intellectualism."^

^Bernard Leach, A Potter*s Book, (Florida: Transatlantic Arts Inc., 1956), p. 107 CHAPTER II

RESEARCH INTO OVERGLAZE COLORANTS

The hlstoploal facts brought out in Chapter I were not without reward* They unveiled to me some of the dimensions and directions for this research* The mystical methods and formula of the past concerning glazes and overglazes no longer seem quite so secretive* The so-called closely guarded secrets of the past can be revealed by experiments* The purpose of this research> aside from the historical revelations and the ability to make a tr\ily authentic statement about pottery in its formation 9 is to resolve the problem of how an effective overglaze decoration can be applied with ceramic coloring oxides. Another purpose was to find a method whereby the colorants could be used inexpensively and readily in the studio*

There is a wide range of commercially prepared overglaze colorants available at a modest cost from various ceramic suppliers* Commercial colorants vary from company to company» whereas a single coloring oxide is everywhere in abundance* By working with a few such oxides one gains a better understanding than a slight familiarity with many commercial colorants*

Spinel9 a colored crystal used as a colorant in place of the metallic oxides, is also available commercially and can be made in the studio* It is not recons&ended unless for advanced experimental work because of the lengthy procedure in its development. The spinel is referred to as a stain* "A spinel stain is a colored crystal that is extremely resistant to the attacks of fluxes in the glaze and the effects 9 of his tes^eratures. In stpiot chemical terms, spinel refers to the mineral magnesium cduminate (MigAl203). Houever, manganese, iron and chromium may be present by replacement. The crystal is an oct€diedron variety of extreme hardness. The ruby gem is a red spinel. By calcin ing certain oxides together, some very stable colored spinels can be formed."^ Besides the spinels, a number of other chemical conqpounds are calcined to produce stable colorants at certain temperatures.

"Calcining means to heat a ceramic material or materials to the tempera ture necessazy to drive off the chemical water, carbon dioxide, and other volatile gases.Altho\igh some fusion may occur, some grinding of the material to a powdery form may be necessary to be used effectively.

Under certain circumstances the use of a raw coloring oxide may be objection able because of its soltiability in the uniting glaze.

Finally with the abundance of information at hand, I began ny experiments. I selected seven different colorants: cobalt oxide, green chrome oxide, copper oxide, tin-vanadium stain, rutile, red iron oxide and manganese dioxide. These are the major coloring oxides and are sufficient to develop most color combinations and are readily available.

With these colorants I used seven glaze t3^8. The flux used often had a distinct effect on the color, therefore a variety of glaze types was used in this experiment. The fluxes used were Cornwall stone, soda feldspar, potash feldspar, spodumene, volcanic ash, and nepheline syenite.

^Glenn C.Nelson, Ceramics, (New York: Holt, Rinehart and Winston, 1966), p. 221 ^Glenn C. Nelson, Ceramics,(New York: Holt, Rinehart and Winston, 1966), p. 312 CHAPTER III

CONE SIX GLAZES

The seven glazes chosen were selected specifically because of their different characteristics and chemical makeup.

They are as follows:

Glaze I

Cornwall Stone 65. Whiting 15. BaU Clay 8. Kaolin 2. Dolomite 2.5 Colemanite 2.5 Flint 5. Barium Carbonate 7.

The major ingredient is Cornwall Stone, with a high preponder*

ance of magnesia and lime. This glaze tends to be somewhat translucent

and shiny.

Glaze II

Soda Feldspar 50. Dolomite 16. Barium Carbonate 6 • Kaolin 9. Whiting 3. Flint 17. Bentonite 3.

The major ingredient is soda feldspar with a concentration of dolomite fliix. The addition of 5% zinc makes this glaze surface very

smooth and mat. The buttery feel is magnificent. 11

Glaze III

Feldspar Potash 60. Nepheline Syenite 10. Whiting 10. Kaolin 3. Flint 17. Bentonite 3.

The major ingredient is feldspar potash with the addition of nepheline syenite and whiting as auxiliary fluxes. The glaze is very

critical. It is very mat if underfired, a satin mat at cone six, and

shiny if overfired.

Glaze IV

Lepidolite 15. Spodumene 25. Ferro Frit 312«* 10. Whiting 10. Barium Carbonate 15• Kaolin 3. Flint 18. Colemanite 5. Bentonite

This is undoubtedly my favorite glaze. With additions of

Kaolin this glaze will mat, with talc and zlrcopax a beautiful blue white translucency effect, and increasing the colemanite and adding

soda ash a copper red will develop with copper.

Glaze V

Volcanic Ash 63• Kaolin 7. Dolomite 8. Flint 20. Colemanite 10. Bentonite 3.

This is basically a good transparent glaze to use over underglaze decorations and to combine with overglaze colorants. 12

Glaze VI

Potash Feldspar 55• Whiting 15. Kaolin 5. Flint 15. Colemanite 3. Bentonite 3.

One of my earliest glazes that is just a good all around glaze, and many variations with colorants are easily adaptable.

Glaze VII

Nepheline Syenite 65. Feldspar Potash 25. Whiting 15. Kaolin 15. Talc 15. Flint 10.

This is a somewhat dry mat and very critical at cone six. The glaze has many possibilities.

To each of these glazes, depending upon the overglaze colorants, was added between 8 to 12% of zircopax and 5 to 10% talc.

The development of the glazes was many years in the making. They were all found to work very effectively at cone six. IH of these materials is the melting of the two together and then reground for the purpose of eliminating the soluability and toxic effects» Many colors cannot be obtained with the pure metallic oxides because they have a low melting point and tend to volatize.

The answer to question was really quite obviouse Why not use the same basic ingredients as the seven base glazes because they contain the necessary chemical conq>onents in the making of a colorant that could be applied as an overglaze decoration and remain stable.

The colors chosen were blue, green, yellow, orange, red-brown and brown. With each of the glazes I used the following proportions.

The base refers to the glaze itself combined with the various oxides.

§1 Blue #4 Yellow

Base 2.5 Base 2.5 Cobalt Oxide 10.0 Tin Vanadium Stain 10.0 #2 Green #5 Orange Base 2.5 Green Chrome Base 3.0 Oxide 5.0 Rutile 8.0 Zircopax 2.0 #3 Blue Green #6 Red-Brown Base 2.5 Base 2.5 Copper Oxide 7.0 Red Iron Cobalt Oxide 3.0 Oxide 10.0

#7 Brown

Base 2.5 Manganese Dioxide 5.0

The results trare excellent. The stains can be combined for many other color combinations. These combinations no doubt will depend upon the decoration and form of the pottery. CHAPTER V

RESULTS or CONE SIX GLAZES AND 0VER6LAZE COLORANTS

The test tile experiments proved very successful. The ratio range of the base glaze to the colorant was found to be 1.25 to 5.»

1.25 representing the base glaze» and 5. the colorant.

The series of test tile experiments have been mounted and will be on display for anyone to use for classroom work in the ceramics studio at the University of Minnesota, Duluth. The experiments can only be seen on the completed tiles, and they are a vital part of the decoration on the pottery completed for my graduate show. The photographs Included in this paper are indicative of the results of my research. Following are ten plates taken from my graduate exhibit. i

91 iK

'I

II 18

These are some examples of my research into glaze colorants. The

surface has only been scratched.

Many colors and textures can be obtained with the intermixing of the overglaze colorants. It is a beginning for those who wish to continue the experiments. To some it will add a new dimension in decoration. CHAPTER VI

CONCLUSIONS

This research has added a new dimension to my work as a studio potter. Rather than using the prepared commercial stains, or developing spinel stains in a lengthy process, the artist potter may explore the possibilities of combining oxides with various base glazes. The basic technique of painting on pottery has been somewhat vague for many years, but many nuances of color and texture are possible. Each potter can discover technical resoiirces which seem to have been designed for him.

The only area which was not fully covered in this report was the adjustments made in percentages of bases to oxides. Experimentation on this can be made by those undergraduates who wish to avail themselves of an exciting dimension in pottery.

This has been a very dramatic and rewarding esq^erience for me.

It has created enthusiasm and interest among those undergraduates with whom I have worked and opened an exciting experience for me. BIBLIOGRAPHY

Arias* Greek Vase Painting* New York: Harry W. Abram Inc*g 1961*

Beazley, J, D. Development of Attic Black Figure. University of Califoraia Press, 1951.

Cox, Warren E. The Book of Pottery and Porcelain. New York: Crown Publishers, 1940.

Leach, Bernard. A Potter's Book. Florida: Transatlantie Arts Inft.. 1956.

Matz, Freiedrich. Art of Crete and Early Greece. New York: Greystone Press, 1962.

Nelson, Glenn C. Ceramics. New York: Holt, Rinehart and Winston, 1956.

Noble, Joseph V. Ceramics Monthly. Columbus: Dec. 1965.

Parmelle, Cullen W. Ceramic Glazes. Chicago: Industrial Publications, Inc., 1951. •

Rhodes, Daniel. Clay and Glazes for the Potter. Philadelphia: Chilton Co., 1957.

Rhodes, Daniel. 6 Porcelain. Philadelphia: Chilton Co., 1959,