Enamels. A species of vitreous varnish, colored by means of metallic oxides {see No. 2393 (Violet Enamels)) and applied in a thin stratum to brightly polished metallic surfaces (copper or gold), on which it is fused by the flame of a blowpipe, or by the heat of a small furnace. The basis of all enamels is a highly transparent and fusible glass, called frit, flux, or paste.

2379. Base Frit or Flux for Enamels

2379. Base Frit or Flux for Enamels. The precise qualities of the products of the following processes depend greatly upon the duration and degree of heat enfployed. By increasing the quantity of sand, glass, or flux, the enamel is rendered more fusible, and the opacity and whiteness is increased by the addition of oxide of tin. The use of borax should be avoided, or used very sparingly, as it is apt to make the enamel effloresce and lose color.

I.  Red lead, 16 parts; calcined borax, 3 parts; powdered flint glass, 12 parts; powdered flints, 4 parts; fuse in a Hessian crucible for 12 hours, then pour it out into water, and reduce it to a powder in a biscuit-ware (unglaz-ed porcelain) mortar.

II.  Powdered flints, 10 parts; nitre and white arsenic, of each 1 part as last.

III.  Flint glass, 3 ounces; red lead, 1 ounce; as last.

IT. Red lead, 18 parts; borax (not calcined), 11 parts; flint glass, 16 parts; as last.

V.  Flint glass, 6 parts; flux No. II, above, 4 parts; red lead, 8 parts; as last.

VI.  Tin, 2 to 5 parts; lead, 10 parts; calcine in an iron pot at a dull cherry-red heat, and scrape off the oxide as it forms, observing to obtain it quite free from undecomposed metal; when enough of the dross is obtained, reduce it to fine powder by grinding and elu-triation (see No. 14 (Elutriation)), then mix 4 parts of this powder with an equal weight of pure sand or powdered flints, and 1 of sea-salt, or other alkaline matter; fuse the mixture in a Hessian crucible, and proceed as before. The best proportions of the tin and lead, for all ordinary purposes, are about 3 of the former to 10 of the latter. The calcined mixed oxides are commonly called calcine.

VII.  Lead and tin, equal parts; calcine as above; and take of the mixed oxides, or calcine {see preceding receipt) and ground flints, of each 1 part; pure subcarbonate of potash,

2 parts; as before.

VIII.    Lead, 30 parts; tin, 33 parts; calcine as before, then mix 50 parts of the calcine with an equal weight of flints, in powder, and 1 pound of salts of tartar; as before. A fine dead white enamel.

2380. Black Enamels

2380.    Black Enamels. I. Pure clay,

3 parts; protoxide of iron, 1 part; mix and fuse. A fine black.

II.  Calcined iron (protoxide), 12 parts; oxide of cobalt, 1 part; mix, and add an equal weight of white flux. (See No. 2396 (Dead-White Enamel).)

III.  Peroxide of manganese, 3 parts; zaffre, 1 part; mix and add it as required to white flux. Zaffre is crude oxide of cobalt.