Enamel, in general, signifies a' vitrefied matter, interspersed with some solid substance; and possessing all the pfoperties of glass, excepting that of transpar-ency.
The basis of enamels is a pure crystal glass or frit, ground together with a fine calx of lead and tin, prepared for that purpose, with the addition of a small proportion of the white salt of tartar. These form the principal ingredients of all enamels, which are made by adding various pulverized colours, and thoroughly incorporating the whole in a furnace. For white enamel, it is sufficient to add manganese to the matter which constitutes the basis; for azure, zaffre mixed with calx of brass; for green, calx of brass with scales or iron, or crocus mams ; for black, zaffre with manganese or crocus martis, or manganese with tartar ; for red, manganese, of calx of copper with red tartar; for purple, manganese with calx of brass ; for yellow, tartar and manganese; lastly, for violet coloured enamel, manganese with brass, that has been three times calcined.
Enamels are used either for the counterfesiting or imitating of precious stones, and for painting ; or by enamellers and artists working in gold, silver, and other metals.— That species of enamel which jewellers employ, is imported from Holland, or Venice, in small cakes of various sizes, which are in general about 4 inches in diameter, and have the mark of the maker indented oh them. It pays a duty of 3s. 8d. per pound on importation ; and is allowed a drawback of ls.6d. per lb. on being again exported.
Enamelling, is the art of laying enamel upon metals, such as gold, silver, copper, etc. whether plain or painted. The latter process is performed on plates of gold or silver, but generally on those 0f copper, prepared with the white enamel ; on which certain objects are delineated with the colours, and afterwards burnt in the fire, where they acquire a brightness and lustre resembling glass.
Painting in enamel is held in greater estimation than any other branch of that art; on account of* its peculiar and permanent vivacity, the strength of its colours not being effaced by time, but always retaining their pristine splendour. It is chiefly employed in miniature, as it cannot be easily performed on a large scale; the enamel being very liable to crack on a plain surface, so that even the smallest plates must be somewhat of a convex form.