GLOSSARY OF CERAMIC TERMS

CLAY

A malleable material made from decomposing rock, formed while wet into shapes, then solidified through exposure to high temperatures.

 

There are three main categories of clay used in the production of functional and decorative ceramics:

 

EARTHENWARE:  A low fired clay body that is porous unless glazed. Examples of glazed earthenware are faïence, delftware, majolica, and maïolica.

STONEWARE:  A clay body fired in the range of 2100 degrees Fahrenheit resulting in a sturdy product that is impervious to liquids even without a glaze. Due to large amounts of impurities, stoneware is not as translucent as porcelain.

PORCELAIN:  A clay body produced from combining two white clays, kaolin and petuntse. High temperature firing results in a product that is strong, white, vitrified, impervious to liquids and resistant to thermal shock. True porcelain was discovered in China in the Tang Dynasty (618-9070 and reproduced in Europe in the early eighteenth century.

Biscuit:  Unglazed porcelain or earthenware that has been fired only once.

Bone china:  A mixture of clay (25%) and kaolin (25%) to which bone ash (50%) is added, producing a modified porcelain perfected by Josiah Spode around 1796.

Ceramics:  Any objects made of a fired clay body, such as earthenware, stoneware or porcelain.

Creamware:  Cream-colored, lead glazed earthenware developed by Wedgwood and others in the mid-eighteenth century.

Faïence:  Any glazed porous earthenware. Originally the French name for the tin glazed earthenware made in Faenza, Italy in the sixteenth century.

Feldspar:  Known as petuntse in China, it is an essential ingredient of most true porcelain fused under a high temperature into a kind of natural glass. It is also used for glazing.

Firing:  The process for transforming a clay object into pottery or porcelain by exposing it to the requisite degree of heat.

Fritware:  Invented in Iraq in the ninth century, a type of pottery in which a glassy material is mixed with clay and the surface is tin glazed to look like Chinese porcelain.

Gilding:  Application of gold to ceramic body, used either as leaf or mixed with honey or mercury.

Glaze:  Form of glass, coated or sprayed over the ceramic form. The glaze becomes smooth, hard and translucent after firing and renders the surface impermeable.

Kaolin (China clay):  Fine white clay that remains white after firing. Kaolin is an essential component of true porcelain.

Kiln:  A type of oven in which ceramics are fired.

Maïolica:  A decorated type of earthenware having an opaque glaze, usually fired at low temperature and produced in Italy. The technique of tin glazing was developed by the Assyrians some 3,000 years ago. From the eighth to the eleventh centuries, Persian and Egyptian examples of tin glazed ware were exported to Spain. By the thirteenth century, Italians were importing tin glazed wares from Majorcan traders.

Majolica:  A trade name used by Minton and others for a type of earthenware characterized by ornate and intricate forms and decorations in brightly colored lead glazes.

 

Petuntse:  A form of feldspar containing silicate of potassium and aluminum that is an essential ingredient of porcelain. Fused under high temperature into a kind of natural glass, it gives porcelain its hardness and transparency.

 

Pottery:  A generic term for all ceramic wares without exception, but in normal use it is employed to designate all wares which are not porcelain.

 

Slip:  Liquid or diluted clay used to decorate pottery.

 

Soft paste porcelain:  A type of porcelain made from a clay body containing glassy grit and fired at a comparatively low temperature. Also known as artificial porcelain, fritted porcelain, and pâte tendre.

Tin-glazed earthenware:  Low fired earthenware objects with a white tin oxide glaze base coat. Such objects can remain white or be decorated. The glossy white ware in some cases was intended to resemble the surface of Chinese porcelain. It is known as delftware and majolica in England, Delftware in Holland, faïence in France, and maïolica in Italy.

Transfer printing:  The process of decorating ceramic wares by inking an engraved copper plate and printing the design on paper which is then pressed on the surface of the ware to release the pattern and create a surface decoration. The image is fixed by subsequent firing.

Bibliography

David Battie, Sotheby's Concise Encyclopedia of Porcelain, Conran Octopus, Ltd, London, 1990.

A.E. Dodd, Dictionary of Ceramics, George Newnes Ltd., London, 1967.

John Cushion, An Illustrated Dictionary of Ceramics, Van Nostrand Reinhold Co., New York, 1974.

George Savage and Harold Newman, An Illustrated Dictionary of Ceramics, Thames & Hudson, 2000.