Stoneware

Jian ware tea bowl with "hare's fur" glaze, southern Song dynasty, 12th century, Metropolitan Museum of Art (see below)[1]

Stoneware is a rather broad term for pottery or other ceramics fired at a relatively high temperature.[2] A modern technical definition is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay.[3] Whether vitrified or not, it is nonporous (does not soak up liquids);[4] it may or may not be glazed.[5] Historically, across the world, it has been developed after earthenware and before porcelain, and has often been used for high-quality as well as utilitarian wares.

As a rough guide, modern earthenwares are normally fired in a kiln at temperatures in the range of about 1,000°C (1,830 °F) to 1,200 °C (2,190 °F); stonewares at between about 1,100 °C (2,010 °F) to 1,300 °C (2,370 °F); and porcelains at between about 1,200 °C (2,190 °F) to 1,400 °C (2,550 °F). Historically, reaching high temperatures was a long-lasting challenge, and temperatures somewhat below these were used for a long time. Earthenware can be fired effectively as low as 600°C, achievable in primitive pit firing, but 800 °C (1,470 °F) to 1,100 °C (2,010 °F) was more typical.[6] Stoneware also needs certain types of clays, more specific than those able to make earthenware, but can be made from a much wider range than porcelain.

Glazed Chinese stoneware storage jar from the Han Dynasty

Stoneware is not recognised as a category in traditional East Asian terminology, and much Asian stoneware, such as Chinese Ding ware for example, is counted as porcelain by local definitions.[7] Terms such as "porcellaneous" or "near-porcelain" may be used in such cases. One definition of stoneware is from the Combined Nomenclature of the European Communities, a European industry standard. It 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.[4][8]

Industrial types

In industrial ceramics, five basic categories of stoneware have been suggested:[9]

  • Traditional stoneware – a dense and inexpensive body. It is opaque, can be of any colour and breaks with a conchoidal or stony fracture. Traditionally made of fine-grained secondary, plastic clays which can be used to shape very large pieces.
  • Fine stoneware – made from more carefully selected, prepared, and blended raw materials. It is used to produce tableware and art ware.
  • Chemical stoneware – used in the chemical industry, and when resistance to chemical attack is needed. Purer raw materials are used than for other stoneware bodies. Ali Baba is a popular name for a large chemical stoneware jars of up to 5,000 litres capacity used to store acids.[10]
  • Thermal shock resistant stoneware – has additions of certain materials to enhance the thermal shock resistance of the fired body.
  • Electrical stoneware – historically used for electrical insulators, although it has been replaced by electrical porcelain.
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