|
Stoneware is a vitreous or semi-vitreous ceramic made primarily from stoneware clay or non-refractory fire clay.〔''Standard Terminology of Ceramic Whiteware and Related Products: ASTM Standard C242''.〕 Stoneware is fired at high temperatures.〔(Clay vitrifying temperatures )〕 Vitrified or not, it is nonporous;〔Arthur Dodd & David Murfin. ''Dictionary of Ceramics''; 3rd edition. The Institute of Minerals, 1994.〕 it may or may not be glazed.〔Encyclopedia Britannica (Jasperware is unglazed stoneware )〕 ==Definition and description== 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."〔 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.〔Cuff, Yvonne Hutchinson. ''Ceramic Technology for Potters and Sculptors.'' London: A.&C. Black, 1994, p. 64.〕 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.〔Cripss, J.C.; Reeves, G.M.; and Sims, I. ''Clay Materials Used in Construction.'' London: The Geological Society, 2006, p. 408.〕 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.〔Rhodes, Daniel and Hopper, Robin. ''Clay and Glazes for the Potter.'' Iola, Wisc.: Krause Publications, 2000, p. 109.〕 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.〔Paul Rado ''An Introduction to the Technology of Pottery''; 2nd ed. Oxford: Published on behalf of the Institute of Ceramics by Pergamon, 1988 ISBN 0-08-034932-3〕 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.〔W. Ryan & C. Radford. ''Whitewares: production, testing and quality control''. Oxford: Published on behalf of the Institute of Ceramics by Pergamon, 1987 ISBN 0-08-034927-7〕 Six categories of stoneware have been suggested:〔F. Singer & S. S. Singer. ''Industrial Ceramics''. London: Chapman & Hall, 1963〕 * 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 * Italian stoneware - a mix of different clays including a stoneware clay that can be fired at higher temperatures and provides added strength to 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.〔''Dictionary Of Ceramics''. Arthur Dodd & David Murfin. 3rd edition. The Institute Of Minerals. 1994.〕 * 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."〔Arthur Dodd & David Murfin. ''Dictionary of Ceramics''; 3rd edition. The Institute Of Minerals, 1994.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「stoneware」の詳細全文を読む スポンサード リンク
|