stoneware

stoneware, hard pottery made from siliceous paste, fired at high temperature to vitrify (make glassy) the body. Stoneware is heavier and more opaque than porcelain and differs from terra-cotta in being nonporous and nonabsorbent. The usual color of fired stoneware tends toward gray, though there may be a wide range of color, depending on the clay. It has been produced in China since ancient times and is the forerunner of Chinese porcelain. It is difficult to distinguish between early porcelaneous stoneware and true porcelain. During the Ming dynasty (1368-1644) a porcelainlike stoneware was developed with remarkable red and green glazes. In the 16th cent. it was extensively manufactured in Yixing in Jiangsu prov., which is notable for its unusual teapots of red, buff, or gray and glazed or enameled stoneware. In Europe stoneware was manufactured in the 12th cent. in Germany, especially in the north and on the lower Rhine. Early salt-glazed wares have been found at Aachen and Cologne; these grayish, blue, and brown wares were exported in quantity to the Lowlands and England. Dutch, Flemish, and German potteries of the late 14th cent. made a distinctive stoneware, known as Cologne ware or grès de Flandres, with stamped or profusely modeled decoration; most of the examples exhibit a lead glaze, though a cream-colored variety was usually left unglazed. In the 1670s, John Dwight started to make stoneware jugs and mugs in England and climaxed his work with remarkable figurines and portrait busts of porcelaneous stoneware. By the turn of the century a white salt-glazed ware was being widely produced in Staffordshire. In the last quarter of the 18th cent. Josiah Wedgwood invented and developed two stonewares that are still justly prized: basalt ware and jasper ware. Stoneware remains one of the most common forms of ceramics and is often employed in commercial and industrial products. See porcelain.

Pottery fired at a high temperature (about 2,200 °F, or 1,200 °C) until vitrified (made glasslike and impervious to liquid). Because stoneware is nonporous, glaze is applied only for decoration. Stoneware originated in China circa 1400 BC and was exported to Europe in the 17th century. This red to dark-brown stoneware was copied in Germany, England, and the Netherlands. Seealso bone china, porcelain.

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Stoneware a vitreous or semivitreous ceramic ware of fine texture, made primarily from nonrefactory fire clay. Its maturation temperature ranges from about 1200°C to 1315 °C. In essence, it is man-made stone. One widely recognized 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 and is not impervious to liquids. Porcelain, which some consider to be a type of stoneware, is distinguished as being whiter than stoneware and always vitreous. Kaolin, or China Clay, has a lower content of impurities than many other clays. It is also fired to a vitreous state, transforming the constituent silica into glass. Some porcelain bodies are translucent after firing. 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. Potters refer to combinations of clays mixed with other materials as clay bodies. Different kinds of clay bodies are created by mixing additives, such as feldspar, grog, quartz, flint, many other minerals are used and these can include spodumene, wollastonite to modify clays. Clay bodies can thereby be formulated to fire at a range of temperatures. Darker clays often contain iron and other metal oxide impurities. The clay used for porcelain and white stoneware clay bodies contain very little of these impurities.

Glaze may be applied to stoneware pottery before a second firing at a different temperature, or a glaze may be applied before a single, raw firing. American Stoneware became the dominant houseware of nineteenth century America.

See also

• Coade stone

References

Combined Nomenclature of the European Communities - EC Commission in Luxembourg, 1987

External links

• Beardman jugs from the Avondster site -- Provides photographs and history of early Rhenish stoneware vessels, produced circa 1500s-1700s.
• Japanese stoneware in the collection of the Asia Society.