stoneware

The tradition & historical record

Stoneware is a broad class of pottery fired at a relatively high temperature, to be impervious to water. A modern definition is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay. This definition excludes stone vessels that are carved from a solid piece of stone. End applications of stoneware include tableware and decorative ware such as vases. Stoneware is fired at between about 1,100 °C (2,010 °F) to 1,300 °C (2,370 °F). Historically, reaching such temperatures was a long-lasting challenge, and temperatures somewhat below these were used for a long time. ¹

It was developed independently in different locations around the world, after earthenware and before porcelain. 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. Terms such as "porcellaneous" or "near-porcelain" may be used in such cases. Traditional East Asian thinking classifies pottery only into "low-fired" and "high-fired" wares, equating to earthenware and porcelain, without the intermediate European class of stoneware, and the many local types of stoneware were mostly classed as porcelain, though often not white and translucent. One definition of stoneware is from the Combined Nomenclature of the European Communities, a European industry standard. ¹

Five basic categories of stoneware have been suggested: ¹

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. Has largely been replaced by chemical porcelain. 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 Electrical stoneware: historically used for electrical insulators, although it has been replaced by electrical porcelain. Another type, Flintless Stoneware, has also been identified. It is defined in the UK Pottery (Health and Welfare) Special Regulations of 1950 as: "Stoneware, the body of which consists of natural clay to which no flint or quartz or other form of free silica has been added." ¹

The compositions of stoneware bodies vary considerably, and include both prepared and 'as dug'; the former being by far the dominant type for studio and industry. Nevertheless, the vast majority will conform to: plastic fire clays, 0 to 100%; ball clays, 0 to 15%; quartz, 0%; feldspar and chamotte, 0 to 15%. The key raw material is either naturally occurring stoneware clay or non-refractory fire clay. The mineral kaolinite is present but disordered, and although mica and quartz are present their particle size is very small. Stoneware clay is often accompanied by impurities such as iron or carbon, giving it a "dirty" look, and its plasticity can vary widely. Non-refractory fire clay may be another key raw material. Fire clays are generally considered refractory, because they withstand very high temperatures before melting or crumbling. Refractory fire clays have a high concentration of kaolinite, with lesser amounts of mica and quartz. Non-refractory fire clays, however, have larger amounts of mica and feldspar. ¹

Stoneware can be once- or twice-fired. Maximum firing temperatures can vary significantly, from 1100 °C to 1300 °C depending on the flux content. Most commonly an oxidizing kiln atmosphere is used. Typically, temperatures will be between 1180 °C and 1280 °C. To produce a better quality fired-glaze finish, twice-firing can be used. This can be especially important for formulations composed of highly carbonaceous clays. For these, biscuit firing is around 900 °C, and glost firing (the firing used to form the glaze over the ware) 1180–1280 °C. After firing, water absorption should be less than 1%. ¹

The Mature Indus Valley civilization (2600-1900 BC), produced stoneware bangles, within its urban centers. Early examples of stoneware have been found in China, naturally as an extension of higher temperatures achieved from early development of reduction firing, with large quantities produced from the Han dynasty onwards. In both medieval China and Japan, stoneware was very common, and several types became admired for their simple forms and subtle glaze effects. Japan did not make porcelain until about 1600, and north China (in contrast to the south) lacks the appropriate kaolin-rich clays for porcelain on a strict Western definition. Jian ware in the Song dynasty was mostly used for tea wares, and appealed to Buddhist monks. Most Longquan celadon, a very important ware in medieval China, was stoneware. Ding ware comes very close to porcelain, and even modern Western sources are notably divided as to how to describe it, although it is not translucent and the body often grey rather than white. In China, fine pottery largely consisted of porcelain by the Ming dynasty, and stoneware was mostly restricted to utilitarian wares and those for the poor. Exceptions to this include the unglazed Yixing clay teapot, made from a clay believed to suit tea especially well, and Shiwan ware, used for popular figures and architectural sculpture. In Japan many traditional types of stoneware, for example Oribe ware and Shino ware, were preferred for chawan cups for the Japanese tea ceremony, and have been valued up to the present for this and other uses. ¹

In contrast to Asia, stoneware could be produced in Europe only from the late Middle Ages, as European kilns were less efficient, and the right sorts of clay less common. Some ancient Roman pottery had approached being stoneware, but not as a consistent type of ware. Medieval stoneware remained a much-exported speciality of Germany, especially along the Rhine, until the Renaissance or later, typically used for large jugs, jars and beer-mugs. "Proto-stoneware", such as Pingsdorf ware, and then "near-stoneware" was developed there by 1250, and fully vitrified wares were being produced on a large scale by 1325. The salt-glazed style that became typical was not perfected until the late 15th century. ¹

England became the most inventive and important European maker of fancy stoneware in the 18th and 19th centuries, but there is no clear evidence for native English stoneware production before the mid-17th century. German imports were common from the early 16th century at least, and known as "Cologne ware", after the centre of shipping it rather than of making it. ¹

The text above is adapted from the Wikipedia article “Stoneware”, available under the Creative Commons Attribution-ShareAlike 4.0 licence. ¹

stoneware is vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay, according to the structured record cited below. This entry was generated automatically from that record and has not yet been reviewed by a person familiar with the tradition. ²

The source record links this tradition to 35 external registers, which can be verified through the citation. ²