Stoneware

A Staffordshire stoneware plate from the 1850s with transferred copper print – (From the home of J. L. Runeberg)

Definition and description

A handpainted stoneware bowl produced in Portugal in 2008

A Chinese stoneware vase from the Song Dynasty, 11th century

One widely-recognised definition 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."^[3]

The key raw material in stoneware 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.^[5] 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.^[6]

Formulations for stoneware vary considerably, although the vast majority will conform to: plastic fire clays, 0 to 100 percent; ball clays, 0 to 15 percent; quartz, 0 to 30 percent; feldspar and chamotte, 0 to 15 percent.^[7]

Stoneware can be once-fired or twice-fired. Maximum firing temperatures can vary significantly, from 1100 °C to 1300 °C depending on the flux content.^[8] Typically, temperatures will be between 1180 °C to 1280 °C, the higher end of which equate to Bullers Rings 38 to 40 or Seger cones 4 to 8. 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. Water absorption of stoneware products is less than 1 percent.^[9]

Five categories of stoneware have been suggested:^[10]

• 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 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.^[11]
• 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."^[12]

History and notable examples

The earliest examples of stoneware have been dated to 1900 BCE in the Indus Valley Civilization.^[13] An industry of a nearly industrial-scale mass-production of stoneware bangles flourished in the Indus Valley throughout the civilization's Mature Period (2600-1900 BCE).^[14][15]

Another early example of stoneware has been found in China, naturally as an extension of higher temperatures achieved from early development of reduction firing.^[16] From the various definitions of high-fired ceramics, it is agreed that the earliest stoneware is encountered in the late Shang dynasty in China, with large quantities in production by the Han dynasty.^[17][18]

Other notable historical examples include:

• American Stoneware - The predominant houseware of 19th century North America.
• Bartmann jug - A type of decorated stoneware that was manufactured in Europe throughout the 16th and 17th centuries, especially in the Cologne region of Germany.
• Böttger Ware - A dark red stoneware developed by Johann Friedrich Böttger. It is a very significant stage in the development of porcelain in Europe.^[19][20][21]
• Cane Ware - An eighteenth-century English stoneware of a light brown colour. It was a considerable advance on the coarse pottery that preceded it but, for use as tableware, cane ware was soon displaced by white earthenware. During the 19th and the earlier part of the 20th century, cane ware continued to be made in South Derbyshire and the Burton-on-Trent area as kitchen-ware and sanitary-ware. It had a fine-textured cane-coloured body with a white engobe on the inner surface often referred to as cane and white.^[11][22][23]
• Crouch Ware - A light-coloured Staffordshire salt-glazed stoneware from the early 18th century. It is credited as being one of the earliest examples of stoneware made in England.^[24] It was made from a clay from Crich, Derbyshire, the word "crouch" being a corruption.^[25]
• Rosso Antico - A red, unglazed stoneware made in England during the 18th century by Josiah Wedgwood.^[26] It was a refinement of the redware previously made in North Staffordshire by the Elers.^[11][27]

See also

• Coade stone
• Earthenware

Notes and references

Notes

References

External links

• Beardman jugs from the Avondster site—Provides photographs and history of early Rhenish stoneware vessels, produced circa 16th century-18th century.
• Japanese stoneware in the collection of the Asia Society.