Kaolin

Kaolin, or CHINA CLAY, is fine white clay used in making porcelain. Like less pure clays, it is essentially a hydrous silicate of alumina, but it is a comparatively rare substance. The clays found in most localities contain iron in sufficient quantity to colour them red or buff when burned in a kiln, but China clay is of a pure, or nearly pure white both before and after it is fired. This, together with its refractory nature, makes it of great value in the manufacture of porcelain, of which it forms the chief ingredient. It is also used to a considerable extent by paper-makers, and in less quantity in the making of some chemical products. Kaolin is a product of the decomposition of the feldspar of a granitic rock. The name Kaolin is derived from the Chinese Kao-ling, 'high ridge,' the name of hills near King-tih-chin in Chiang-hsi, a chief seat of the porcelain manufacture in China. Clay from this district was sent to Europe early in the 18th century by Jesuit missionaries; similar clay was discovered in Saxony; and about 1755 it was discovered in Cornwall, whence the chief English supplies are obtained, some being also obtained in Devonshire—in all, about 30,000 tons a year. Kaolin is found in France, and in Nebraska and other states of the American Union; in the United States the annual consumption is some 18,000 tons. See CORNWALL, FELSPAR, POTTERY.