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Ceramics and Glass Terminology [1]
Biscuit - Ceramic ware that has been fired once but not yet glazed.
Bisque - Unglazed vitreous china.
Blown Glass - Either free blown or blown into a mold.
Body - Formulation of clays used in making a piece of pottery.
Crimping - Decoration in which dents or flutes are tooled onto a glass vessel when viscous; results in a wavy pattern.
Crystal Glass - Brilliant, colorless glass with a high proportion of lead.
Cut Glass - Glass that has a pattern cut with a grinding wheel.
Earthenware - Soft ceramic bodies fired at relatively low temperatures; varies in color from brown to red to buff, depending on the clay. Earthenware needs to be glazed in order to be impervious to water; historically, such glazes were made with lead.
Enameling - Method of decorating glass and ceramics in which a mixture of powdered glass and a fusing flux is painted and then fired onto the surface.
Flux - Material added to glazing compounds to aid fusing.
Glaze - Thin layer of glass that, when fired, renders ceramics impervious to water; compounded of silica in combination with various fluxes.
Greenware - Ceramics that have not been biscuit fired.
Lead Glass - Glass with lead oxide used as a flux; lead reduces the viscosity of the mixture and lengthens the hardening period, adding strength and brilliance.
Lead Oxide, Red Lead - Basic fluxing material used in compounding early ceramic glazes.
Molded Glass - Glass that has been blown, pressed, or cast into a mold; small pieces of glass cane can also be fused in a mold (millefiori).
Overglaze - Decoration, such as enameling, that has been applied over the basic glaze and fired at a low heat to fuse the pigment
Pontil Mark - Rough place on the bottom of a glass object where the ponti! rod was broken away; sometimes ground off or polished smooth.
Press Molding - Process by which pliable clay slabs are pressed into molds.
Pressed Glass - Glass that has been dropped into a mold and pressed into shape with a plunger.
Stoneware - Hard-bodied ceramic fired at a high temperature. Stoneware is hard, vitreous, opaque, and generally waterproof. Usual colors are gray, brown, or buff, and sometimes red or white.
Salt Glaze - Used only with stoneware; salt, thrown into the high temperature oven, vaporizes to combine with silica and alumina in the clay, producing a thin vitreous fIlm.
Semiporcelain (Soft Paste) - Composed of white clays and a glassy frit in imitation of true porcelain. Semiporcelain, sometimes referred to as bone china, is hard, white, glassy, and occasionally translucent.
Slip - Mixture of clay and water used to cover or decorate a porous clay body, such as earthenware, prior to firing.
Slip Casting - Technique in which liquid clay is poured into plaster molds.
Sprigging - Press-molded clay ornaments applied with water or slip to an unfIred body.
Terra-cotta - Literally "burnt earth;" generally used to describe wares made from naturally occurring clay in a range of colors from pinkish to a deep red upon firiing. Terra-cotta is usually unglazed.
Transfer Printing - Technique in which an engraved copper plate is used to print a design onto thin tissue paper; the design is then transferred to a previously fired ceramic body prior to glazing.
True Porcelain (Hard Paste) - Translucent, vitrified ware that has been fIred at a high temperature; composed of kaolin and feldspar.
Tin Oxide - Added to lead glaze to render the glaze opaque such as in delft or majolica ceramic wares.
Underglaze - Decoration, such as slip, applied directly to the body of a ceramic piece prior to firing.
Vitrify - To become glassy through fusion of melting ceramic particles; vitrifIed ware becomes nonporous and nonabsorbent.
[1] Based largely on 'A Glossary of Terms Useful in Conservation'. Phillimore, Elizabeth. 1976. Ottawa: Canadian Museums Association and the ceramics glossaries in: 'The Moravian Potters of North Carolina'. Bivins, John, Jr. 1972. Chapel Hill: The University of North Caroline Press and 'Decorative Arts'. Craft, Meg. 1992. In 'Caring for Your Collections', edited by Harriet Whelchel. New York: Harry N. Abrams, Inc.