The Cornwall kaolin of England and the Limoges kaolin of France are the best known. English china clays contain little or no iron oxide, and the yellow clays contain only organic materials that can be bleached out. The best grades of English clay are used for coating and lling paper. Cornish clay, known as china stone, is used for the best grades of porcelain glazes. Cheaper grades of kaolin, called mica clay, are used for earthenware glazes and as an absorbent and oil purifying. Kaolin fiber of extreme neness, with average diameter of 118 μin. (3 μm), is made from kaolin containing about 46% alumina, 51% silica, and 3% iron and titanium oxide. It withstands continuous temperatures to 2000°F (1093°C). Kaowool, of Babcock and Wilcox, is kaolin ber in the form of insulating blankets, and kaolin paper is made from the bers compressed to thicknesses up to 0.08 in. (0.20  cm) with or without a binder. It withstands temperatures of up to 2000°F (1093°C) and is used for lters, separators, and gaskets.