The type of pottery known as salt glaze or salted is created by adding common salt, a composition of sodium and chlorine, into the chamber of a hot kiln. This can be done by tossing salt packettes into kiln peepholes or other openings. Sodium acts as a flux or melting agent and reacts with the silica in the clay body. A dilute form of hydochloric acid is given off as a vaporous by-product.

Salt fumes have a dramatic effect on clay under heat. Salt reacts at temperatures from about 1660 °F (904 °C), the melting point of common salt, when a surface blush of color is formed on clays and clay slips, to over 2350 °F (1287 °C), the traditional temperature of high fired salt ware. At the higher temperatures, salt becomes an active vapor. A typical salt glaze has a glassine finish, usually with a glossy orange-peel texture, enhancing the natural color of the clay beneath it.

Salt fire techniques were first introduced in the 15th century, probably in the Rhineland of Germany. At that time, the process was used on a low fire earthenware clay which was "once fired," heated in a continuous arc from bone dry raw clay to finished ware. However, it was soon adapted to stoneware which is usually fired in two stages, a "bisque" fire and a final "high" fire. This two stage process heats clay to a semi-vitrous state (usually up to approximately 1800 degrees F) and then allows the ware to cool to room temperature. Bisque ware is often decorated in some fashion before being returned to the kiln for firing to a near vitrious state.

Historically, salt kilns were used in many areas of Europe, particularly Germany, Scandinavia and the British Isles. Salt kilns were also popular during the colonial period in North America and in the early years of the United States. The use of salt as a glazing element generally reduced or eliminated the use of high silica glaze compounds by these craftsmen.

Modern Salt Ware

Historic salt firing techniques were revived and adapted by English potter and artist Bernard Leach. They were also introduced into Japanese pottery through Leach's association with Japanese potter, Shoji Hamada , in the 1950's. American studio potter Don Reitz introduced salt glazing into the curriculum at Alfred Universy, New York in 1959. Potters and salt kilns in both North and South Carolina are well known for producing modern salt fired ware, as are American universities with strong ceramic programs. These include Alfred University in New York and Utah State University in Logan, Utah.

Modern potters using traditional salt processes are working in many areas of the United States and Europe. The unique salt glaze finish entices modern potters as it provides an opportunity to capture spontaneous changes in atmosphere and color and is a tool for ongoing experimentation and creativity.

Salt can also be used as a decorative element on 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 .

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.

Reference

• Hamer, Frank and Janet. The Potter's Dictionary of Materials and Techniques. A & C Black Publishers, Limited, London, England, Third Edition 1991. ISBN 0-8122-3112-0.