Salt glaze pottery
[7][8][9] The earliest known production of salt glazed stoneware was in the Rhineland of Germany around 1400;[10] it was effectively the only significant innovation in pottery of the European Middle Ages.
By the 15th century, small pottery towns of the Westerwald, including Höhr-Grenzhausen, Siegburg, Köln, and Raeren in Flanders, were producing a salt-glazed stoneware,[11] with the Bartmann jug a typical product.
[14] Whilst its manufacture in America increased from the earliest dated production, the 1720s in Yorktown, significant amounts were imported from Britain until around the mid-19th century.
[19][20] In a related patent application, which was granted in 1671, he also claimed to have "discovered the mystery of transparent earthenware commonly knowne by the name of porcelaine or China and Persian ware.
[22] During the 1830s and 1840s, considerable amounts of salt-glazed sewer-pipes were produced by Doultons following Sir Edwin Chadwick's advocacy of improved sanitary conditions.
[23] Also, from about 1830, they started production of salt glaze stoneware vessels, which were valued for their acid resistance, for the emerging chemical industries.
By 1890 their decorative stoneware were so successful that 350 designers and artists were employed at the Lambeth factory, including the famous George Tinworth.
[24][23] Doulton’s Lambeth factory closed in 1956, due largely to new clean air regulations that prohibited the production of salt glaze in the urban environment.
The body should ideally be richer in silica than normal stoneware, and iron impurities can help produce good salt glazes.
Any remaining sodium oxide will form salt by reacting with hydrochloric acid vapour as the gases exit the kiln.
[1] The general reaction is shown below, with the values for x and y varying dependent on the amounts of sodium oxide, alumina and silica composing the glaze: Salt can also be used as a decorative element on selected individual pots.
Salt can also be added, in solution, to coloured clay slips and can be sprinkled onto biscuit ware in protective, ceramic containers called saggars.
