A fine kind of semi-transparent earthenware, in imitation of that made in China, and hence called China-ware. The combination of silex and argil is the basis of porcelain; and, with the addition of various proportions of other earths, and even of some metallic oxides, forms the different varieties of pottery, from the finest porcelain to the coarsest earthenware. Though silicious earth is the ingredient which is present in largest proportion in these compounds, yet it is the argillaceous which more particularly gives them their character, as it communicates ductility to the mixture when soft, and renders it capable of being turned into any shape on the lathe, and of being baked. The clays are native mixtures of these earths; but they are often rendered unfit for the manufacture of at least the finer kinds of porcelain, from other ingredients which they also contain. The perfection of porcelain will depend greatly on the purity of the earths of which it is composed; and hence the purest natural clays, or those consisting of silex and argil, alone are selected.
Two substances have been transmitted to Europe as the materials from which the Chinese porcelain is formed, which have been named Kaolin and Petunse. It was found difficult to procure in Europe natural clays equally pure, and hence, in part, the difficulty of imitating the porcelain of the East, Such clays, however, have now been discovered in different countries; and hence the superiority to which the European porcelain has attained. The fine Dresden porcelain, that of Berlin, the French porcelain, and the finer kinds which are formed in this country, are manufactured of such clay, which, from the use to which it is applied, has received the name of porcelain earth, and which appears in general to be derived from the decomposition of felspar of granite. It appears, also, that natural earths containing magnesia are used with advantage in the manufacture. The proportion of the earths to each other must, likewise, be of importance; and from differences in this respect, arise, in part, the differences in the porcelain of different countries, as well as the necessity frequently of employing mixtures of natural clays.
The argil communicates tenacity and ductility to the paste, so that it may be easily wrought; the silex gives hardness and infusibility; and on the proper proportion of these depends, in a great measure, the perfection of the compound. The proportion of silex in porcelain, of a good quality, is at least two-thirds of the composition; and of argil, from a fifth to a third. Magnesia is of use by lessening the tendency which the composition of silex and argil alone has to contract in baking, which is inconvenient in the manufacture. See Pottery.