Ginna's Quick Guide to Ceramics


stoneware cupStoneware is most often encountered by hobbyists in the form of hand-built or hand-thrown pottery. (We do not generally fire stoneware.)

Stoneware is fired much hotter than earthenware. It matures between Cone 8 and Cone 11 (1200—1315C / 2200—2400F). In essence, it is man-made stone. This concise definition is from the Combined Nomenclature of the European Communities, which states:

"Stoneware, which, though dense, impermeable and hard enough to resist scratching by a steel point, differs from porcelain because it is more opaque, and normally only partially vitrified. It may be vitreous or semi-vitreous. It is usually coloured grey or brownish because of impurities in the clay used for its manufacture, and is normally glazed."

(In contrast, earthenware is fired at lower temperatures, is not impervious to liquids, and can be scratched by metal.)

Firing a piece of pottery to too high a temperature will result in warping or melting. Vitreous clay bodies can be made at different temperatures ranges, but they are typically fired in the stoneware/porcelain range.

Fired stoneware absorbs up to 5% water, porcelain 0%, and earthenware up to 10%. Earthenware, when moist, is typically not freeze resistant.

Clay refers to group of minerals that generally exhibit plasticity when mixed with water, and which chemically primarily consist of alumina and silica. Different kinds of clay are created by mixing additives to modify the clay and formulate it to fire at a range of temperatures.   Adapted from Wikipedia