Stoneware is a mixture of clay and other particles that allows it to be fired to a high temperature. Often silica, talc and feldspar are added to clay to make it easier to work. It is coarse gray/white or tan clay that can be supplemented with grog (coarse pieces of sand, broken or dried clay) to increase durability and add texture. The advantage of stoneware over traditional clay bodies is that stoneware is non-porous and sturdy. It is hardy and can endure high temperatures in an oven or microwave. Pizza stones and the tiles in high temperature wood ovens are often made of stoneware.
Many minerals and chemical compounds used in high gloss glazes won’t melt and adhere at lower temperatures. The high temperatures (2400 F) stoneware is fired to allows a significantly vast diversity in processes and combinations for glazes that other clay bodies cannot tolerate. Stoneware can also be manipulated in reduction and oxidation techniques.
Stoneware is almost identical to porcelain, but contains more iron and other impurities. It is coarse, while porcelain is smooth, but both can be fired to high temperatures that accentuate the luster and detail of the piece. To differentiate between porcelain and stoneware, hold it to light. Porcelain has a translucent body, while stoneware is opaque. To differentiate between stoneware and earthenware, pick up the piece, stoneware feels heavy. If the piece is chipped, you can scrape at the exposed clay, if it flakes or breaks, it is earthenware. Stoneware won’t crumble or break.
Stoneware and porcelain made the scene in China about 2,000 years ago by the Han Dynasty (206 B.C.–A.D. 220). They built a multi chamber kiln on a slope with a fire-box on one end that pushed the hot air through the chambers. Their ability to produce stoneware had more to do with the clay deposits than the kiln itself. Europe didn’t produce a high fired ware until the early 1800’s.
Stoneware is becoming a preferred medium for ceramicists because of the durability. If a piece can maintain through a tumble or fall, it saves countless hours of reproduction. It also opens avenues for glaze combinations and is widely available at most art centers.
Stoneware also makes practical utensils for eating and drinking.