ENAMEL fen older form amel, Fr. email, OF. esmail, It. smalto, from OHG. smalz, Ger. Schmalz, butter, from sehmelzen, to melt, Gk. padetv, meldcin, to melt). A glaze coating ap plied by fusion to any subslanee which will bear the necessary heat, especially to metals and to pottery (q.v.). Enamel is really a kind of glass, and although it is usually of special composition, in order to produce an easily fusible material, the name is applied rather to glass when used in certain special ways. In the purely utili tarian employment of 'enamel, its purpose is to proteet the surface to which it is applied from the action of corrosive substances. Thus, the liability of iron to oxidation when exposed to heat or moisture, and to corrosion by even the weakest acids, has led to ninny attempts to coat it with a protecting surface. For this purpose coatings of various materials have been employed (see 'aux), the most efficient has been found to he enamel. The earlier enameled ware was usually thick, but enamel is now successfully ap plied to sheet iron and sheet steel. The utensils are pressed out of the sheet metal according to the process described under DIES AND DIE-SINK ING, and under HOLLOW WARE. The metal foundation having been properly prepared by annealing to stand the heat, it is dipped in the melted glaze and fired in an oven similar to that employed fur the glazing of pottery, which is kept at a temperature of about 1500° F. The
constituents of the glaze and their proportions vary in the different factories, and are carefully guarded trade secrets. The color of enameled ware is determined by the metallic oxides used in the glaze, and does nut materially alter the character of the enamel, although a pure white enamel is likely to be loss tough than gray. The quality of the enamel depends not only on the character of the glaze, but also upon the number of coats applied. Ify one process four successive coats are applied, the first three of which are simply dried, while the fourth is burned at 1500° F. In another, two successively fused coats are applied. In the cheaper grades of enamel ware arsenic is said to be used in place of the oxide of tin, thus decreasing the cost, according to the statement of a leading manufacturer, by 75 per cent. Agate-ware is simply a trade name for a variety of enameled ware, so called on ac count of its mottled appearance. Enameled ware, even of the highest grade, is likely to be injured by excessive heat, which, by making the iron expand faster than the glaze, cracks the latter. It is also liable to be affected by acids wherever there is the slightest break in the con tinuity of the surface of the enamel. When once acid penetrates the surface so it can act on the iron underneath, it will gradually undermine the glaze so that it peels off.