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 Hessian
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 glass, 3 oz.; red lead, 1 oz.; as last.
5. (Wynn.) Red lead, 18 parts; borax (not calcined), 11 parts; flint glass, 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 processes depend greatly upon the duration and degree of heat employed. 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 it should be used sparingly, as it is apt to make the enamel effloresce and lose colour.
Enamel, Black. Prep. 1. Calcined iron (protoxide), 12 parts; oxide of cobalt, 1 part; mix, add an equal weight of white flux, and fuse as before.
2. (Clouet.) Pure clay, 3 parts; protoxide of iron, 1 part. A fine black.
3. Peroxide of manganese, 3 parts; zaffre, 1 part; mix, and add it, as required, to white flux.