ENAMELS. - These are metallic surfaces covered with a thin coating of glass of various colours, and which is sometimes partially transparent, but generally opaque. The enamel or glass is ground to powder, mixed with some vehicle, such as turpentine, or oil of spike, and spread on as a thick coating of paint, and when dried, the whole is heated just sufficiently to fuse the enamel, and cause it to adhere to the metal.

The work is placed within a muffle, which is in many cases a miniature arched vault open at one end, placed in the midst of a small furnace, and surrounded by burning fuel, which keeps it at the red heat, although the fuel cannot possibly touch the work. In other cases the furnace is made of sheet iron; it then measures externally about 20 inches long, 12 wide, and 10 deep, and is mounted on wrought iron legs that support it, so that the opening or door, which is at the one end, may be on the level with the eye of the artist, whilst from the opposite end proceeds the flue leading into a chimney. The whole apparatus bears some resemblance to a German stove, or rather, to a laundry stove considerably elevated, but the muffle, or a heated chamber corresponding therewith, is always provided for the reception of the work to be enamelled to protect the same from the flame and smoke of the fuel.

Many of the enamelled works can hardly be said to be polished artificially, as the lustre is produced simply by the process of fusion; thus the enamelled faces of watches, when the ground has been fired, only require the figures to be added, as the vitreous surface is mostly smooth enough from the fusion without being polished; and in less favourable cases the work is only ground to a level but dull surface, and afterwards just raised to the melting point, so as to fuse the surface, and thereby give it the polish.

The backs of gold watches and numerous articles of jewellery, including mourning rings, are so enamelled as to show various devices or inscriptions in gold, upon a ground or general surface of enamel; in this case the work is engraved, all the parts where the enamel is to appear being cut away by the graver, and the spaces are afterwards filled in with the pulverised enamel, which is burnt in, and lastly, the whole is polished down to a uniform surface.

Formerly nearly all the enamelled works were polished by the lapidaries, who used, 1st, the horizontal lead mill with fine emery for grinding; 2ndly, lead with rottenstone and water; and 3rdly, the leather lap or buff wheel with putty powder. But the enamellers of the present day mostly polish their own work, and employ either an ordinary lathe with a mandrel upon which the laps are screwed like chucks, the cylindrical edges of the laps being alone used, or else they employ a polishing lathe similar to those of cutlers and others.

The French enamellers commonly select instead of emery, a hard white pulverised porcelain, called white emery, which is manufactured at the Royal Manufactory of Porcelain at Sevres, and they afterwards polish with yellow tripoli; the first is applied on a lead or wooden wheel, and the latter on a buff.

When enamels are polished by hand, the work is first roughed down with slips of water of ayr stone and water, used after the manner of a file; after which the different artists use slips of boxwood, mahogany, or metal, first, with pumice-stone, and then with crocus, nearly as for gold.