ENAM′EL

A species of vitreous varnish, coloured with metallic oxides, applied in a thin stratum to brightly polished metallic surfaces (copper or gold), on which it is fused by the flame of a lamp urged by the blowpipe, or by the heat of a small furnace. The basis of all enamels is a highly transparent and fusible glo , called ‘frit,’ ‘flux,’ or ‘paste,’ which readily receives a colour on the addition of metallic oxides. It may be made by one or other of the following formulæ: Prep. 1. Red lead, 16 parts; calcined borax, 3 parts; powdered flint gla , 12 parts; powdered flints, 4 parts; fuse in a He ian crucible for 12 hours, then pour it out into water, and reduce it to a powder in a biscuit-ware mortar. 2. Tin, 3 parts; lead, 10 parts; mix, 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; then reduce it to fine powder by grinding and elutriation. In this state it is known among enamellers as ‘flux’ or ‘calcine.’ 4 parts of this ‘calcine’ are next mixed with an equal weight of pure sand or powdered flints, and 1 part of sea salt, or other alkaline matter; the mixture is then partially fused in a He ian crucible, by which it undergoes semi-vitrification. 3. (Chaptal.) Lead and tin, equal parts; calcine as above, and take off the mixed oxides or ‘calcine’ and ground flints, of each, 1 part; pure carbonate of potash, 2 parts; and proceed as before. 4. (Wynn.) Flint gla , 3 oz.; red lead, 1 oz.; as last. 5. (Wynn.) Red lead, 18 parts; borax (not calcined), 11 parts; flint gla , 16 parts; as last. 6. (Wynn.) Powdered flints, 10 parts; nitre and white arsenic, of each, 1 part; as last. Obs. The precise qualities of the products of the above proce es depend greatly upon the duration and degree of heat employed. By increasing the quantity of sand, gla , or flux, the enamel is rendered more fusible, and the opacity and whitene is increased by the addition of oxide of tin. The use of borax should be avoided, or it should be used sparingly, as it is apt to make the enamel effloresce and lose colour.