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Salt glaze pottery
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Pottery referred to as salt glazed or salted is created by adding common salt, sodium chloride, into the chamber of a hot kiln. Sodium acts as a flux and reacts with the silica in the clay body. A typical salt glaze piece has a glassine finish, usually with a glossy and slightly orange-peel texture, enhancing the natural colour of the body beneath it.
Technical processSalt fumes have a dramatic effect on clay under heat. When kiln temperatures reach the melting point of common salt, approximately 900 °C (1660 degrees °F), granulated or rock salt can be introduced into a kiln through peepholes or other openings. This results in a surface blush of colour formed on the ware body. At higher temperatures, over 1280°C (2350°F), the traditional temperature of high fired salt ware, salt becomes an active vapor throughout the kiln interior. A dilute form of hydrochloric acid is given off as a vaporous by-product.
First introduced in the 14th century, the process was initially used on earthenware which was fired from green to finished ware in a long, slow cycle. However, the process was soon adapted to stoneware, which can either be fired in a one fire cycle or in two stages, a "bisque" fire and a final "high" fire. This two stage process results in a semi-vitreous state at a lower bisque temperature. Ware is then allowed to cool to room temperature for decoration before a further firing.
Salt can also be used as a decorative element on selected individual pots. Bisque ware can be soaked in a brine solution to create salted patterns. Rope and other textiles can also be soaked in brine and wrapped around bisque ware. Salt can also be added, in solution, to colored clay slips and can be sprinkled onto bisque ware in pottery containers called saggars.
A related method, called soda firing, substitutes soda ash (sodium carbonate, ) and/or sodium bicarbonate (NaHCO3)for salt and is an increasingly common alternative. Unlike salt, which will fume throughout the kiln, soda must be introduced in a manner that spreads it around the ceramic ware, such as by spraying. Soda glaze produces results similar to salt glaze, with subtle variations in texture and color.
HistoryThe unique characteristics of salt glazing were discovered in the Rhineland of Germany, probably in the 14th century. Initially, the process was used on low fire earthenware. By the 15th century, small pottery towns of the Westerwald, including Höhr-Grenzhausen, Siegberg, Köln, and Raeren in Flanders, were producing a salt-glazed stoneware. (Nelson, p. 33-34) Westerwald Pottery was characterized by stamped medallions and the use of a cobalt oxide based colorant for decoration. Salt kilns were used extensively in western Europe in the 16th and 17th centuries, particularly in Germany, Scandinavia and the British Isles.
American salted stonewareSalt ware was also popular during the colonial period in North America and in the early years of the United States. Initially, significant amounts of salt ware was imported from England. Americans began producing salt-glazed stoneware circa 1720 in Philadelphia, Pennsylvania, and Yorktown, Virginia, and American Stoneware became the predominant houseware of nineteenth century America. Contemporary potters in both North and South Carolina are well known for ongoing salt fired production. These independent craftsmen, generally operating small family oriented businesses in rural areas, produce ware in both traditional and personalized forms. Traditionally, each business in this area has been known for their distinctive output and decorative motifs.
Modern Art and Craft salt wareIndustrial salt firing continues. The technique was promoted in the 20th century art and craft sector by English potter and artist Bernard Leach. It was introduced into Japanese craft pottery through Leach's association with Japanese potter, Shoji Hamada, in the 1950s. American studio potter Don Reitz introduced salt glazing into the curriculum at Alfred University, New York in 1959, and this movement has spread to other American universities with strong ceramic programs.
Modern studio potters using traditional salt processes are working in many areas of the world. The unique salt glaze finish captures spontaneous changes in atmosphere and color. The method is considered a tool for ongoing experimentation and creativity.
Other traditional pottery processes which have been revived or modified by modern potters include low-temperature pit firing, the Asian technique of raku and the use of saggar boxes in gas and wood fired kilns.
External links- in the New York State Museum.
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