Staffordshire clay Pipe-clay, 40; kaolin, 25; quartz, 20; felspar, 15. Stone-ware { Felspar, 25; quartz or silex, 25; soda, 25; plastic clay, 15; boracic acid, 10. Porcelain Silica, 66; alumina, 30; potash, 3.4; magnesia and lime, 1.1. Porcelain glaze Silica, 73.4; alumina, 15.7; potash, 7.4; magnesia and lime, 2.2. English porcelain Kaolin, 34; bone, 47; felspar, 19; soda ash, 36. Old Sèvres soft-paste { Saltpetre, 22; sea-salt, 7.2; burnt alum, 3.6; soda { ash, 3.6; gypsum, 3.6; sand, 60. { This was made into a frit and mixed--75 { parts frit, 17 chalk, and 8 of calcareous marl. As to the glazes applied to clay or opaque ware, we have seen that they are broadly distinguished as translucent plumbiferous or alkaline, opaque stanniferous, and salt glaze. The distinction is also to be observed between glaze and enamel, although they are often confounded. Thus, according to M. Brongniart, there are three kinds of glaze--varnish, enamel, and couverte--all of which are vitrifiable. Varnish he describes as a transparent and plumbiferous material, melting at a lower temperature than that required for baking the paste; enamel, an opaque, generally stanniferous (containing tin) substance; couverte, a substance which melts at a temperature equal to that required for baking the paste. Birch, on the other hand, draws a distinction between glaze and enamel. In one place he speaks of “opaque glasses or enamels,” and again, “among the Egyptians and Assyrians, enamelling was used more frequently than glazing.” So, also, Fortnum, who, dividing pottery into soft and hard, subdivides the former into unglazed, lustrous, glazed, and enamelled. The glazed he again divides into silicious, or glass-glazed, and plumbeous, or lead-glazed, both of which are transparent. The word “glaze” is thus more correctly applied to the covering, which does not alter the color of the body upon which it is laid, and “enamel” to that which obscures the body. Glass, or silicious glaze, is formed by fusing sand with an alkali--potash or soda. When to this is added the oxide of lead, transparent plumbiferous glaze is the result; and when to both of these oxide of tin is added, we have opaque stanniferous enamel. The glass and plumbeous glazes may be colored with a variety of other oxides, without losing their transparency. When or where glaze was first applied to clay is not known. Like many other branches of knowledge and many nations, it has its roots in the East, but whether we are indebted for it to India, Egypt, or Assyria, cannot now be decided. Upon this question Dr. Birch says: