Creation of Ceramic Forms Combining Stoneware and Porcelain

CREATION OF CERAMIC FORMS COMBINING STONEWARE AND PORCELAIN

APPROVED s

Major Professor

Minor Professor

Directo)irector of the J0epadepartmeni t of Art

r J <2~ Dean of the Graduate School CREATION OP CERAMIC FORMS COMBINING STONEWARE AND PORCELAIN

THESIS

Presented to the Graduate Council of the North Texas State University in Partial Fulfillment of the Requirements

For the Degree of

MASTER OF ARTS

Charles K, Havis, B. A. Denton, Texas August, 1969 TABLE OP CONTENTS

Page LIST OP TABLES iv

LIST OP ILLUSTRATIONS

Chapter

I. INTRODUCTION 1 Statement of Problem Plan of Experiments Definition of Terms

II. TESTING AND RESULTS Procedure Results

III. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS .... 28 Summary Conclusions Recommendations

BIBLIOGRAPHY 39

iil LIST OP TABLES

Table Page

I. Combinations of Bodies #1 and #3 15

II. Combinations of Bodies #2 arid #4 18

III. Combinations of Bodies #2 and #3 ...... 21

IV. Combinations of Bodies #1 and #4 ...... 24

iv LIST OF ILLUSTRATIONS

Figure Page 1. An Example of Cracking . 4 2. An Example of Crazing 5 3< An Example of Separation 7 4. An Example of Splitting 8 5. Successful Combinations of Bodies #2 and...... 30 CHAPTER I

INTRODUCTION

Working with clay has been one of man's most exciting forms of expression for almost as long as he has been on earth. Possibly it will never be known how long it took man to learn that a fired clay vessel would hold liquids and not crumble or break easily. It is known that long before he learned to fire clay early man was decorating it with marks and with earth pigments.

The Egyptians were the first to make a glaze, probably as early as the fifth millenium B. C., to decorate clay objects (2, p. 15)• The oldest accurately dated glaze was found in the tomb of King Mena (ca. 3300 B. C.) (b, p. 2).

The Chinese are believed to have discovered in the seventh century B. C. the technique of firing clay to tem- peratures so high that the body vitrified and became impervious to liquids (5» P« 25). Stoneware, as this is called, has inherent qualities which have intrigued potters ever since. It can contain liquids without a glaze, the clay can be easily formed and shaped in many different ways, and the raw materials of which stoneware is made are abundant and relatively inexpensive. 1 Porcelain, which has evolved, historically, as a refine- ment of stoneware (7, p. 62), has all of the qualities listed above plus two more; it is white and translucent. The Chinese made no distinction whatever "between stoneware and porcelain# They used one term, tz'u, to describe any piece of pottery that was vitrified and that made a ringing sound when struck (7» P* 8)5 the distinction between stoneware and porcelain is a Western innovation.

Statement of Problem The problem under investigation is the creation of ceramic forms using both stoneware and porcelain in the same piece of ware. Sub-problems are to experiment with the best techniques of joining different clay bodies and the creation of aesthetically pleasing pieces which combine the textural beauty and rich glazes of stoneware with the bright glazes and the white and sometimes translucent body of porcelain.

Plan of Experiments The study was limited to four clay bodies, two of stoneware and two of porcelain. Each stoneware body was used in combination with each of the porcelain bodies. These combinations were joined at two different degrees of moistness, leather-hard and plastic, and were made up of thrown and slab forms. The bodies were joined in this manner in order to determine what effect the consistency of the clay and the way the clay was formed would have upon the adhering of stoneware and porcelain. Technically, the greatest difficulty in this study was caused by the variation in the shrinkage of bodies. Shrinkage, which occurs both in drying and in firing, is related to the physical structure of clay, particularly the purity of the clay and the size of Individual particles* Hence a porcelain body made of koalin, ball clay, and fine ground flint and feldspar will shrink more than a clay body which contains coarser elements such as sand or small rock particles (3, pp. 109-111)* Therefore, if a fine grained body, such as porcelain, is to adhere to a coarser body, such as stoneware, shrinkage would be the most important variable to be considered.

In the process of drying and firing a piece of ceramic ware shrinkage occurs in three different stages. During the drying a piece will shrink until all clay particles are in contact with each other, although there may be water in the pores of the clay and although the particles may still be moist (3» p. 108). The next shrinkage occurs in the latter part of the bisque firing, and the final shrinkage happens during vitrification, when the clay body hardens and tightens. The temperature at which shrinkage happens in the last two stages depends upon the composition of the clay body (6, PP* 13-16). Results were checked and recorded at the end of each of these three stages.

Definition of Terms In this study the following terms will be used as defined. Bisque.—This term refers to unglazed ceramic ware that has "been fired once but not to the stage of vitrification. In this study the pieces were fired to cone 09 (approximately 1700°F). Ware fired to this temperature can "be handled easily and will readily accept a glaze. Cone.—A small pyramid of ceramic materials which softens with a specified heat treatment (combination of heat and time) (3t P- 306). These are placed in front of a spy hole so that they can "be used to Judge if the kiln has reached the desired temperature. Cracks.—A defect that occurs only on the outside or the inside surface of a piece but does not go all the way through the wall of the piece. Figure 1 shows a detail of a piece in which cracking occurred.

Fig. 1—An example of cracking Crazing.—A term used in this study to describe fissures or cracks in a fired glaze caused by tension between the glaze and the clay bodies. This tension occurs when one body shrinks more than the other. An example of crazing is shown in Figure 2.

Fig. 2--An example of crazing

Damp-bin.—An air-tight area in which the drying of ceramics can be controlled. It is usually used to retard the rate of drying. 6

Glaze.-—A thin layer of glass fused onto ceramic surfaces.

Greenware.—A term used for formed pieces that have not been fired (8, p. 17). In this study the term refers to a

"bone-dry piece.

Leather-hard.—"A term for clay ware that has been partially dried; at this stage of drying, the shrinkage has been largely completed."(1, p. 16*0 Clay in this stage is stiff but can still be joined to other pieces with a thick slip.

Matured.—The state of a ceramic body that has reached the desired degree of vitrification (1, p. 177). In this study a ceramic piece has reached maturity when it has been fired to cone 10 (approximately 2300°F).

Oxidation.—In this study a term used to describe the firing of ceramic material in an electric kiln in which the atmosphere is free of carbon.

Plastic.—In describing a clay body this term indicates that the clay particles are still surrounded with a thin film of water. Clay in this state can be shaped without cracking and will retain that shape when the forming stress is re- moved (1, p. 209).

Porcelain.—A vitreous, high-fired clay body that is characterized by whltness, translucency where thin, and hardness, when it has been fired to maturity.

Reduction.—A condition which results from carbon monoxide escaping into the kiln and stealing oxygen molecules from the ceramic materials being fired. This usually causes a change in the color of olay bodies and glazes. Separation.—A term used to describe the pulling apart of the Joint between two clay bodies. This separation is usually caused by unequal shrinkage of the two bodies. An example of complete separation and partial separation is shown in Figure 3*

Fig. 3—An example of separation

Slip.—In this study a word used to describe clay that has been thinned with water to the consistency of thick cream. Splitting.—In this paper the word describes a major fault that runs from the joint into one or the other of the* 8

Fig. k—An example of splitting clay bodies. A split may also extend into both the porcelain and the stoneware bodies. Figure 4 is an example of a split that runs into both of the bodies. Stoneware.—A high-fired clay body that is impervious to liquids and is usually grey, buff, or red. The color results from iron and other impurities in the clay. CHAPTER BIBLIOGRAPHY

1. Dodd, A. E., Dictionary of Ceramics. Totwa, New Jersey, Littlefield, Adams and Co., 1967.

2. Nelson, Glenn C., Ceramics, New York, Holt, Rlnehart and Winston, Inc., I960.

3. Norton, R. H., Elements of Ceramics, Cambridge, Massachusetts, Addison-Wesley Press, Inc., 1952.

4. Parmelee, Cullen W., Ceramic Glazes. Chicago, Illinois, Industrial Publications, Inc., 1948. 5. Rada, Pravoslav, Book of Ceramics. London, Spring Books, undated.

6. Rhodes, Daniel, Clay and Glazes for the Potter. New York, Greeribergi Publisher, 1957* 7. Rhodes, Daniel, Stoneware and Porcelain. New York, Chilton Co., 1959. 8. Van Schoick, Emily C., editor, Ceramic Glossary. Columbus, Ohio, The American Ceramic Society, 19&3« CHAPTER II

TESTING MD HESULTS

The tests with stoneware and porcelain were made over a period of five months in the ceramic laboratory in the Art Department of North Texas State University. The pieces were fired along with the regular student work from the ceramic courses offered "by the university.

Procedure Pour clay "bodies were selected for the testing of the problem. Two of these» the stoneware and porcelain bodies used in teaching ceramics at North Texas State University, the author had worked with over a period of approximately two years. Two were selected from Daniel Rhodes' book Clay and Glazes for the Potter.

The following are the clay formulae for the four bodies used in this study.

Porcelain body #1 Kaolin \ 25 Ball Clay \ 25 Feldspar \ 25 Flint \ 25 The above formula for porcelain is used by the Art De-

•~~Xi partment of North Texas State University. 10 11

Porcelain body #2 (1, p. ^3) China Clay 10 Kaolin 20 Ball Clay 26 Feldspar 2k Flint 20

Stoneware "body #3

A. P. Green Fire Clay 68 Cedar Heights Red Clay 23 Flint 9

The above formula for stoneware is used by the Art

Department of North Texas State University.

Stoneware body #4 (1, p. k-2)

Ball Clay 20 Kaolin kO Red Clay 15 Feldspar 15 Flint 10

The four bodies were used in four combinations of stoneware with porcelain. These combinations are bodies #1 and #3, bodies #2 and #k, bodies #2 and #3, and bodies #1 and #4.

These combinations were Incorporated in objects, either func- tional or decorative, in the following ways»

Thrown plastic stoneware with slab plastic porcelain Thrown plastic stoneware with thrown plastic porcelain Slab plastic stoneware with thrown plastic porcelain Slab plastic stoneware with slab plastic porcelain

Thrown leather-hard stoneware with slab plastic porcelain Thrown leather-hard stoneware with thrown plastic porcelain Slab leather-hard stoneware with thrown plastic porcelain Slab leather-hard stoneware with slab plastic porcelain

Thrown plastic stoneware with slab leather-hard porcelain Thrown plastic stoneware with thrown leather-hard porcelain Slab plastic stoneware with thrown leather-hard porcelain Slab plastic stoneware with slab leather-hard porcelain 12

Thrown leather-hard stoneware with slab leather-hard porcelain Thrown leather-hard stoneware with thrown leather-hard porcelain Slab leather-hard stoneware with thrown leather-hard porcelain Slab leather-hard stoneware with slab leather-hard porcelain.

These combinations were made up in the above manner in order

to determine whether or not the way that clay is formed and

its stage of dryness would have an effect upon joining the

stoneware body and the porcelain body.

The procedure used to join the stoneware and porcelain

bodies was the same that is used to join pieces of a hand-

built form made from a single kind of clay. The porcelain

body and the stoneware body were each scored and then coated

with a thick slip made from an equal mixture of the stoneware .

and porcelain involved, thinned to the consistency of thick

cream. The walls of the two forms were approximately the

same thickness. The two pieces were then forced together

either with the fingers or with a wooden tool. The amount

of pressure used was determined by the condition of the bodies

and the shapes of the forms. (For example, more pressure

could be used to force two leather-hard slabs together than

could be used to force two thrown plastic shapes together without distorting them.)

The pieces were allowed to dry for a short time in the damp-bin and were then left in an open room to complete drying. When the piece became bone-dry, the joints were examined for cracks, splitting, or separations. Evidence of any defects at this Stage was recorded, and if the faults were excessive the piece was destroyed* 13

All forms in which there were no major faults were fired in an electric kiln to cone 09 (approximately 1700°F). These bisque forms were examined to determine the compatability of the two todies, and the results were recorded. Completely separated forms and forms that had major cracking or splitting were destroyed, except in instances where the cracking or splitting enhanced the over-all appearance of the piece.

While the latter were not considered successful, the "best ones were completed as independent projects.

The remaining "bisque pieces were then prepared for the maturation firing. The decision as to whether or not an individual piece should "be glazed was made at the discretion of the artist by the form of the piece. Hence, there is a great deal of variety in the handling of the glazes. Some forms are completely glazed, and others are partially glazed. Glaze on the last group might be applied on the inside or on the out> side only, or it might be applied as a decorative element in areas of different sizes and shapes.

All pieces that were considered successful were placed in a gas kiln and fired to cone 10 (approximately 2300°P).

After this firing the forms were examined and the final results recorded.

Results

The results of the combinations are recorded in four tables that list the combinations and give the results at 14 the end of each of the three stages. The following key ex-

plains the numbering in these four tablest

I s plastic stoneware was joined with plastic porcelain. II » leather-hard stoneware was joined with plastic porcelain. Ill = plastic stoneware was joined with leather-hard porcelain. IV = leather-hard stoneware was joined with leather- hard porcelain. A = thrown stoneware with slab porcelain. B « thrown stoneware with thrown porcelain. C = slab stoneware with thrown porcelain. D = slab stoneware with slab porcelain.

Thirty-two pieces were made by combining body #1 with

body #3. The results of these combinations are shown in

Table I.

There were fourteen pieces in which complete separation

occurred. Of these, seven occurred in the greenware state,

three in the bisque state, and four in the matured state.

In three pieces splitting occurred in the greenware

stage and increased with each firing. Two of these had craz-

ing of the glaze, and one had no faults other than splitting.

Incomplete separation occurred in twelve pieces and was

accompanied by cracking, splitting and crazing of the glaze

if the piece was fired to maturity.

The remaining three had hairline cracks that appeared

at the Joint in the greenware stage and increased with each

firing. 15 TABLE I

COMBINATIONS OP BODIES #1 AND #3 Comb* No* Results IA Greenware—Complete separation occurred in both (2 pes) pieces. IB Greenware—IB-1 had minor separation. (2 pes) IB-2 had hairline splits that extended into both clay bodies. Bisque—IB-1 had complete separation at the joint. In IB-2 the split widened and extended. Matured—In IB-2 the split extended further into the stoneware. IC Greenware—The Joints separated completely with (2 pes) major splitting of the slabs. ID Greenware—The slabs split in both bodies. (2 pes) iBisque—Splitting extended and small cracks appeared between porcelain and stoneware. Matured—Crazing of the glaze occurred at the joints. IIA Greenware—Small splits extended from the joint (2 pes) into the stoneware form. Bisque—Splits extended further, and the joints separated partically. Matured—Splits enlarged in IIA-1. Joint in IIA-2 separated completely. IIB Greenware—IIB-1 had minor separation that (2 pes) occurred all around the joint. In IIB-2 the joint separated completely. Bisque—IIB-1 had no change. Matured—In IIB-1 the glaze filled the separations on the outside and inside. IIC Greenware—Minor separation oocurred at the joints. (2 pes) Bisque—IIC-1 had no change. In IIC-2 the separation of the joint increased •with minor cracking of the poroelain form. 16 TABLE I—Continued Comb. No. Results IIC Matured—In IIC-1 the glaze filled the separation, (oont) IIC-2 had major separation which occurred along one-half of the joint. (This area received heavy reduction.)

IID Greenware—Small cracks appeared along the joints (2 pes) and minor separation occurred. Bisque—Complete separation of the joints occurred. IIIA Greenware—Minor separation of the joints occurred, (2 pes) and the porcelain slabs split where the two bodies were joined. Bisque—More separation occurred and splits developed into the stoneware. Matured—The glaze filled some of the splits, but no other change occurred. IIIB Greenware—No faults occurred. (2 pes) Bisque—IIIB-1 had major separation of the joint. IIIB-2 had minor separation of the joint. . Matured—IIIB-1 separated completely. In IIIB-2 the glaze crazed in the area of the joint. IIIC Greenware—Hairline cracks occurred at the joint (2 pes) and ran into the stoneware slab. Bisque—The oracks increased. Matured—The cracks increased in major proportions. HID Greenware—Minor cracks developed at the joints. (2 pes) Bisque—Minor separation of the joints occurred, with no change in the cracks Matured—No noticable change occurred.

IVA Greenware—Minor separation occurred along the (2 pes) joints. Bisque—Separation of the joints increased with splits developing in the porcelain slab. Matured—Major separation occurred, and the glaze crazed at the joints.

IVB Greenware—IVB-1 had minor separation of the (2 pes) joint. IVB-2 had complete separation of the joint. 17

TABLE I—Continued

Comb. No. Results

IVB Bisque--No change was noted. (cont) Matured—Minor separation increased at the joint.

IVC Greenware—Hairline cracks appeared at the joints. (2 pes) Bisque--No noticeable change occurred. Matured—Minor separation increased at the joints. IVD Greenware--IVD-1 separated completely. IVD-2 had no faults. Bisque—Cracks appeared along joint in IVD-2. Matured--IVD-2 separated completely.

The results recorded in Table I show that bodies #1 and

#3 are not successful when used in combination with each other.

In Table II the results of the combinations of bodies

#2 and are shown. Of the thirty-two pieces made by combining bodies #2 and eighteen had no faults. There were five pieces that had minor cracks on the inside of the stoneware portions, but these cracks did not extend from the joints. Pour pieces had minor splits in the stoneware portion.

These splits, also, did not extend from the joint. All nine of these defects occurred at maturity. In these nine cases, the splitting happened only in the slab stoneware, and the cracking appeared only on the inside of the thrown stoneware.

There were four minor separations. Two took place in the bisque stage and were partially filled when glazed. The other two occurred at maturity. 18

TABLE II COMBINATIONS OP BODIES #2 AND #4 Comb. No. Results IA Greenware—No faults occurred. i(2i)pC3) Bisque—No faults occurred. Matured—Minor cracking occurred inside of the stoneware piece but did not extend from the joint. IB Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—Minor cracking occurred inside the stoneware piece but did not extend from the joint. IC Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—Minor separation of the joints occurred. ID Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—Major splitting occurred in the stoneware slab of ID-1 but did not r/jctend from the joint. ID-2 had no faults. IIA Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred. I IB Greenware—No faults occurred. (2 pes) Bisque—IIB-1 had no faults. IIB-2 had no further cracking. The cracking that occurred in the bisque was filled with glaze.

IIC Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—IIC-1 had no faults. IIC-2 had minor splits in stoneware slab, but these did not extend from the joint. IID Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred. IIIA Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. 19

TABLE II—Continued Comb. No. Results IIIA Matured—Minor cracking In IIIA-1 occurred inside (oont) the stoneware form but did not extend from the Joint. IIIA-2 had no faults. I115 Greenware—No faults occurred. (2 pes) Bisque—Minor separation at the joints occurred. Matured—The separations were filled with glaze. No other change occurred. IIIC Greenware—No faults occurred.1 (2 pes) Bisque—No faults occurred. Matured—No faults occurred. IIIC Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred. IVA Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred. IVB Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred. IVC Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—IVC-1 had no faults. IVC-2 had minor splitting in the stoneware slab, but it did not extend from the joint. IVD Greenware—No fi ults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred.

One piece had minor cracking that happened in the bisque and was filled with glaze at maturity. This set of combinations made from bodies #2 and #4 can be used with limited success as further discussed in Chapter III. 20

The results of the thirty-two combinations made with bodies #2 and #3 are recorded in Table III. Of the forms made from bodies #2 and #3 there were seventeen that separated completely. Two of the pieces separated in the greenware stage, thirteen of the pieces separated in the matured stage. The latter two pieces had received heavy reduction in their final firing.

There Were thirteen pieces that did not achieve complete separation but were separated badly enough to be considered unsuccessful. All were accompanied by either splitting, cracking, or crazing of the glaze. Three of these had major separations that happened in the greenware state. Two were so badly separated and split at the bisque state that they were not fired to maturity. Eight were fired through to maturity.

Of the two remaining pieces one had only minor separation, and one had no faults except that the glaze had crazed and hairline cracks had extended into the stoneware form from the joint. The crazing of the glaze and the hairline cracks were so bad that this piece could not be considered successful.

All of the thirty-two pieces had defects that ranged from complete separation of the joints to crazing of the glazes. 21

TABLE III COMBINATIONS OP BODIES #2 AND #3 Comb. No. Results IA Greenware—Separation occurred all along the joints, (2 pes) Bisque—Complete separation occurred. IB Greenware—Separation occurred all along the joints, (2 pes) Bisque—Complete separation occurred. IC Greenware—The joints completely separated. (2 pes) ID Greenware—Major separation occurred with the (2 pes) porcelain slab cracking and splitting. Bisque—The joints separated completely. IIA Greenware—No faults occurred. (2 pes) Bisque—There were slight separations. IIA-2 had a split develop in the porcelain slab. Matured—IIA-1 had major separation. IIA-2 had minor separation, and the length of the split Increased. Hairline cracks extended from the joint into the stoneware form. IIB Greenware—Minor separation occurred. (2 pes) Bisque—IIB-1 had major separation. In IIB-2 the joint separated completely. Matured—IIB-1 had major separations. Crazing , and long hairline cracks occurred at the un- separated areas of the joint. (This piece received a heavy reduction.) IIC Greenware--The joints separated partially. (2 pes) Bisque—The joints separated completely. IID Greenware--No faults occurred. (2 pes) Bisque—The joints had minor separations. Matured—Major separation occurred, and small cracks extended from the porcelain into the stoneware body. IIIA Greenware—The joints had major separations. (2 pes) Bisque—The joints separated completely. . IIIB Greenware—There were minor separations all around (2 pes) the joints. 22

TABLE III—Continued

Comb. No. Besults

11 IB Bisque—Separations increased, but the joints were (cont) still adhered in places. Matured—Joints were still adhered, but the glaze had crazed over that area. IIIB-2 also had hairline cracks that ran from the joint into the stoneware body. (This piece received a heavy reduction, and IIIB-1 did not.)

IIIC Greenware—Minor separation of the joints occurred. (2 pes) Bisque—The joints separated completely.

HID Greenware—The joints separated badly, and the slabs had split in many places. These pieces were destroyed.

IVA Greenware— No faults occurred. (2 pes) Bisque—Minor separation occurred. Matured—IVA-1 had complete separation with hairline cracks that extended from the joint into . the stoneware. (This piece received heavy reduction.) IVA-2 had no change from the bisque. (This piece was in the top of the kiln and received no noticeable reduction.)

IVB Greenware—IVB-1 had major separations at the joint. (2 pes) IVB-2 had no faults. Bisque—No change occurred. Matured—The glaze had crazed where the joint was still adhered, and hairline cracks had extended from the joints into the stoneware body. (These pieces received a heavy reduction.)

IVC Greenware—The joints had minor separations. (2 pes) Bisque—The separations had increased. Matured—No increase in the separations occurred, but the stonu^are slabs developed splits.

IVD Greenware—Hairline cracks occurred at the joints. Minor separation occurred, and the slabs began to split. Bisque—Major increase in separation and more splitting occurred in the slabs. These pieces were destroyed. 23

This set of combinations made from "bodies #2 and #3 is

unsuitable for a successful adhering of stoneware with

porcelain.

The results of the thirty-two combinations made with

bodies #1 and are given in Table IV. Of these thirty-two

forms there were nine pieces that had no defects.

Minor separation took place in seven pieces. These sep-

arations appeared in the matured state with the exception of

one which happened in the bisque state. The bottom of one of

the separated pieces was cracked. This crack was approximately

six inches from the joint. The fault seemed to be caused by

unequal thicknesses of the wall and and bottom of the form

rather than by the Joining of the two bodies.

Minor cracking occurred in eleven pieces. In two pieces

the cracking began in the bisque stage, and in the other nine

these minor faults happened In the matured state. The bottom

cracked in one of these forms also, but as before, it appeared

to be caused by unequal thicknesses of the wall and bottom

rather than by the joining of the two bodies.

Splitting occurred in five pieces. These splits appeared

first in the greenware stage, showed no change in the bisque

stage, but increased in the matured stage.

The combinations of bodies #1 and #4 recorded in Table IV proved to be unsatisfactory. More than two-thirds of the forms attempted were defective. This combination of bodies 24

TABLE IV

COMBINATIONS OF BODIES #1 AND #4

Comb. No. Results

IA Qreenware—No faults occurred. (2 pes) Bisque—IA-1 had no faults. IA-2 had minor separation at the joint. Matured—No change occurred. IB Greenware—Splits appeared in stoneware forms. (2 pes) Bisque—No change occurred. Matured—Major increase occurred in splits.

IC Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—Minor cracking occurred around the joints.

ID Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—The joints had minor separations, and cracks extended into the stoneware forms.

IIA Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred.

IIB Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured--IIB-1 had no faults. IIB-2 had minor separation of the joint, and the "bottom of the piece was cracked approximately six inches from the joint. There appears to be no relationship between the crack and the joint.

IIC Greenware--N^ faults occurred. (2 pes) Bisque—Small, cracks appeared in the joints, and a split extended through the porcelain slabs. Matured--Minor Increase in cracks occurred. IID Greenware—IID-1 had no faults in the joint but (2 pes) a split extended through the porcelain slab. IID-2 had no faults. Bisque—No change occurred. Matured—Small cracks appeared at the joints, but no change occurred in the split of the porcelain slab in IID-1. 25

TABLE IV—Continued

Comb. No. Results

IIIA Greenware--No faults occurred. (2 pes) Bisque—No faults occurred. Matured—IIIA-1 had no faults. IIIA-2 had partial separation at the joint. IIIB Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—The joints had minor cracking and separation.

IIIC Greenware—No faults occurred. (2 pes) Bisque—Minor cracking occurred at the joints. Matured—IIIC-1 had no change. IIIC-2 had no change in the joint, but the bottom of the piece had cracked. The joint was about six inches from the bottom and there seemed to be no relationship between the crack and the joint.

HID Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured--IIID-1 had small cracks at the joint. IIID-2 had no faults.

IVA Greenware—Large splits extended deep into the por- (2 pes) celain slabs from the joints. Bisque—No change occurred. Matured—Minor cracks appeared in the joints. The splits grew larger and extended into the stoneware forms.

IVB Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—No faults occurred.

IVC Greenware—No faults occurred. (2 pes) Bisq1*;—No faults occurred. Matured—No faults occurred. IVD Greenware—No faults occurred. (2 pes) Bisque—No faults occurred. Matured—IVD-1 had minor cracking in the joint. IVD-2 had no faults. 26 is considered to "be unsuitable for physical combinations of stoneware and porcelain.

Of the four sets of combinations only that set of combinations which used bodies #2 and can be considered successful. A very limited success was obtained from using bodies

#1 and bodies but there were not enough pieces without defects to draw any conclusions. CHAPTER BIBLIOGRAPHY

1. Rhodes, Daniel, Clay and Glazes for the Potter, New York, Greenbergi Publisher, 1957-

27 CHAPTER III

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

Summary

The purpose of this study was to create ceramic forms "by using stoneware and porcelain in the same piece of ware. These

forms were made by experimenting with the physical joining of

two porcelain bodies with two stoneware bodies in an aesthetic way in four sets of combinations. These combinations were

concerned with the way a piece was formed and with the moistness of the different clay bodies.

Conclusions

Physical Combinations

Combinations of bodies #1 and #3 and bodies #2 and #3 were unsuccessful. All of the forms involved in these two

sets of combinations developed faults, such as, separation

of the joints, splitting and cracking of the clay bodies,

crazing of the glaze, or, as in many pieces, a combination

of all of these. Unequal shrinkage of the coarse grained

stoneware body #3 and the finer grained porcelain bodies #1 and #2 was the major cause of these combinations lack of success.

There was enough difference in the expansion and con- traction of stoneware body;and porcelain body #1 to cause

28 29 their combination to have a very limited success. The pieces made from this combination of clays developed splits, cracks, and separations to such an extent that only nine of the thirty- two pieces were without defeotsj no relationships could be drawn from the successful pieces. The physical combinations of bodies #1 and #3 and bodies #2 and #3 will not be discussed further in this conclusion and are considered unsuitable for a physical joining of stoneware and porcelain. However, their aesthetic combinations will be considered later. Of the four groups of combinations only the one that used bodies #2 and is considered to have been physically successful. These two bodies owed their success to the fact that they had a close relationship through their clay ingredients. Examples of these successful combinations are shown in Figure 5. Combinations made from bodies #2 and #^, as described in Table II, resulted in eighteen successful pieces out of the thirty-two forms attempted. There were seven combinations in which both pieces of each combination had no faults. These combinations were the followingi 1. IIA in which thrown leather-hard stoneware was joined with slab plastic porcelain. 2. IID in which slab leather-hard stoneware was joined with slab plastic porcelain. 3» IIIC in which slab plastic stoneware was joined with thrown leather-hard porcelain. f- 30

Fig. 5--Sucoessful combinations of bodies #2 and 31

4. HID In which slab plastic stoneware was joined with slab leather-hard porcelain. 5. IVA in which thrown leather-hard stoneware was joined with slab leather-hard porcelain. 6. IVB in which thrown leather-hard stoneware was joined with thrown leather-hard porcelain. ?. IVD in which slab leather-hard stoneware was joined with slab leather-hard porcelain. There were four other forms without faults, but each had a companion piece with defects. These forms were the following! 1. ID-2 in which slab plastic stoneware was joined with slab plastic porcelain. 2. IIB-1 in which thrown leather-hard stoneware was joined with thrown plastic porcelain,

3. IIC-1 in which slab leather-hard stoneware was joined with thrown plastic porcelain.

IV G-1 in which slab leather-hard stoneware was joined with thrown leather-hard porcelain.

There appears to have been a certain amount of stress in stoneware body that caused it to split and crack in the final firing. This could probably be overcome by adding a fine filler such as flint or.calcined clay to the clay body (11 p» 24). 32

Moisture Content

Leather-hard with leather-hard.—In relation to the moisture content of the two "bodies when they were joined, the most successful ceramic forms came from the combinations that were Joined when both bodies were leather-hard. These combinations resulted in a total of seven out of eight sat- isfactory forms. There were three combinations in which both pieces of each combinations had no faults. These pieces were the following»

1. IVA in which thrown leather-hard stoneware was joined with slab leather-hard porcelain.

2. IVB in which thrown leather-hard stoneware was joined with thrown leather-hard porcelain.

3. IVD in which slab leather-hard stoneware was joined with slab leather-hard porcelain.

There was one other form without defects, but its companion piece was unsuccessful. This piece was IVC-1 in which slab leather-hard stoneware was joined with thrown leather- hard porcelain.

Plastic with plastlc.—In the forms made by joining plastic stoneware with plastic porcelain only one piece was successful. This piece was ID-2 in which slab plastic stoneware was joined with slab plastic porcelain.

Leather-hard stoneware with plastic porcelain.—When leather- hard stoneware was used in combination with plastic porcelain, .33

six pieces had no faults. There were two combinations in

which "both examples had no faults. These were the followingi

1. IIA in which thrown leather-hard stoneware was

joined with slab plastic porcelain.

2. IID in which slab leather-hard stoneware was joined

with slab plastic porcelain.

There were two other forms without faults, but each had a

companion piece that was defective. These were the following!

1 * IIB-1 in which thrown leather-hard stoneware was

Joined with thrown plastic porcelain.

2. IIC-1 in which slab leather-hard stoneware was

joined with thrown plastic porcelain.

Plastic stoneware with leather-hard porcelain.—When

forms were made by joining plastic stoneware with leather-

hard porcelain, there were four successful pieces. These were the following«

1. IIIC in which slab plastic stoneware was joined with

thrown leather-hard porcelain.

2. HID in which slab plastic stoneware was joined with slab leather-hard porcelain.

Forming of the Clay Bodies

Slab with slab.--In considering the way that a piece was formed the largest number of pieces without defects were made by the slab with slab combinations. A total of seven out of eight of these were successful. In three combinations 31±

of slab with slab both examples of each were without defects.

These were the following!

1. IID In which slab leather-hard stoneware was used in

combination with slab plastic porcelain.

2. HID in which slab plastic stoneware was used in

combination with slab leather-hard stoneware.

3. IVD in which slab leather-hard stoneware was used

in combination with slab leather-hard porcelain.

There was one other form without defects, but its companion

piece was unsuccessful. This piece was ID-2 in which slab

plastic stoneware was used in combination with slab plastic

porcelain.

Thrown stoneware with slab porcelain.—When two bodies were used in combinations of a thrown stoneware with a slab

porcelain there were four successful pieces. These followt

1. IIA in which thrown leather-hard stoneware was joined with slab plastic porcelain.

2. IVA in which thrown leather-hard stoneware was joined with slab leather-hard porcelain.

Thrown stoneware with thrown porcelain.—There were three

successful pieces which combined thrown stoneware with thrown porcelain. In one combination of thrown with thrown both pieces were successful. This combination was IVB which combined thrown leather-hard stoneware with thrown leather-hard porcelain. The other successful piece made by combining thrown stoneware with thrown porcelain was IIB-1 which used 35

thrown leather-hard stoneware in combination with thrown

plastic porcelain. Its* companion piece was defective.

Slab stoneware with thrown porcelain.—When slab stone-

ware and thrown porcelain were used in combinations together,

there were four forms without defect. In only one of these

oombinations were both without faults. This was IIIC in

which slab plastic stoneware was Joined with thrown leather-

hard porcelain. Two other pieces made by joining slab

stoneware with thrown porcelain were successful, but their

companion forms were not. These were the followingt

1. IIC-1 which was made by joining slab leather-hard

stoneware with thrown plastic porcelain.

2. IVC-1 which was made by joining slab leather-hard

stoneware with thrown leather-hard porcelain.

Aesthetic Combinations

Aesthetically, the combinations which involved the

stoneware body #3 and the porcelain bodies #1 and #2 were

much more appealing than the combination that used stoneware

bodies #4- and porcelain bodies #1 and #2. The texture and

color of this stoneware, warm buff to dark brown, empha-

sized the white and smooth poroelain bodies. When a glaze

was fired on these combinations,, the portion that covered

the stoneware was broken in colo-** and texture and contrasted

well with the sharp, clear appearance that the same glaze

made on the porcelain. These combinations were usually very handsome and delightful to the sense of touch. 36

Stoneware body #*f was grey in color and had a "washed-

out" look when It was combined with porcelain bodies #1 and

#2. Its appearance improved when it received a good reduction,

at which time it became a warm reddish buff which worked well

aesthetically with the porcelain bodies. Because of its lack

of impurities stoneware body produced no special results

in the glaze, such as color that was mottled or broken. The

combinations were usually very subtle in appearance. The tex-

tures of the fired pieces were not as satisfying to the touch

as those that evolved from stoneware body #3 combinations.

Becommendat ions

Based upon the experiments carried out in this study,

the most successful results were obtained from combining

stoneware body and porcelain body #2 in slab with slab

combinations when both bodies were in the leather-hard stage.

These two bodies are recommended for use without further de-

tailed research when they are used in the state Just indicated.

Further study is recommended which Involves an addition

of porcelain grog to bodies #1 and #2. This addition would

cause them to shrink less and make them more physically com-

patible with the coarse stoneware body #3.

Further experimentation with the splitting and cracking

of the pieces should be carried out to determine if these 37 defects could "be used In a positive manner in order to en-

hance a piece, or give it a more earthy appeal. The design

possibilities of these faults if controlled could out-weigh any adverse effects that they might have.

What happens to porcelain and stoneware combinations when they receive a good reduction should be given further

study. There is reason to believe from the recorded results

in the tables that reduction plays a part in separation of

the bodies and the crazing of the glaze that was applied to

them. This question might be investigated by using combinations but in an electric kiln with an oxidation atmosphere

to determine if reduction is responsible for some of these defects.

In this investigation it has been found that a stoneware body can be combined with a porcelain body. These combinations can be obtained without any special adhering or firing techniques and are not limited to the artist potter but can be carried out in a school laboratory parallel with other student work. It is hoped that the artist potter and the student will take advantage of the aesthetic qualities made possible by the Joining of stoneware and porcelain and will add them to their list of skills. CHAPTER BIB LIOGBAPHX

1. Hhod.es, Daniel, Clay and Glazes for the Potter, New York, Greenbergj Publisher, 1957*

38 BIBLIOGRAPHY

Books

Nelson, Glenn C. , Ceramics. New York, Holt, Hinehart and Winston, Inc., i960. Norton, R. H., Elements of Ceramics, Cambridge, Massachusettes, Addison-Wesley Press, Inc., 1952. Parmelee, Cullen W., Ceramic Glazes, Chicago, Illinois, Industrial Publications, Inc., 19^8. Rada, Pravoslav, Book of Ceramics, London, Spring Books, undated.

Rhodes, Daniel, Clay and Glazes for the Potter, New York, Greenbergj Publisher, 1957*

Rhodes, Daniel, Stoneware and Porcelain. New York, Chilton Co., 1959.

Publications of Learned Organizations

Van Schoick, Emily C., editor, Ceramic Glossary, Columbus, Ohio, The American Ceramic"~Society, 1963.

Encyclopedia Articles

Dodd, A. E., Dictionary of Ceramics, Totwa, New Jersey, Littlefleld, Adams and Co., 1967.