Porcelain

(pors'-lcn). An impure silicate of aluminum, non -transparent and exceedingly infusible. It is made from porcelain-clay, or kaolin, derived from feldspar rock bv the atmospheric proce known as " weathering." Heated in a furnace, it loses water, and a porous ma is produced. In making porcelain the powdered kaolin is mixed with water to a thick paste, and then molded into the desired shape. A little feldspar, chalk, or gypsum is added to the clay in order to form a fusible silicate, in quantity just sufficient to bind the particles of clay rirmly together. Upon firing, as the proce is called, a porous " biscuit-ware " is obtained, which is afterward subjected to the proce of glazing. For the finest porcelain the glazing material is feldspar;for the cheaper varieties a mixture of clay, chalk, ground-flints, and borax is used. Earthenware is salt-glazed. There are also other methods of glazing. The colors used in decorating porcelain consist of various metallic oxids, and may be applied before or after glazing. P.-gla , a gla which resembles porcelain, made by fusing cryolite, a double fluorid of aluminum and sodium, with sand. P. Teeth, mineral teeth; incorruptible teeth; silicious terrolic teeth; vilrescent teeth; dental substitutes, resembling, more or le closely, the shape and color of the natural teeth, so constructed that they may be securely fixed to the various attachments employed for their adjustment and retention in the mouth. They composed of feldspar, silex, and other mineral substances.