In crystallizing tin plate the figures are more or less beautiful, according to the degree of heat and relative dilution of the acid. Place the tinplate, slightly heated, over a tun of water, and rub its surfaces with a sponge dipped in a liquor composed of 4 parts of aqua fortis and 2 of distilled water, holding 1 part of common salt or salt ammoniac in solution. Whenever the crystalline spangles seem to be thoroughly brought out, the plate must be immersed in water, washed with a feather or a little cotton (taking care not to rub off the film of tin that forms the feathering), forthwith dried with a low heat, and coated with a lacquer varnish, otherwise it loses its luster in the air. If the whole surface is not plunged at once into cold water, but if it be partially cooled by sprinkling water on it, the crystallization will be finely variegated with large and small figures. Similar results will be obtained by blowing cold air through the pipe on the tinned surface, while it is just passing from the fused to the solid state.
(2) Sulphuric acid, 4 ounces; of water, 2 to 3 ounces, according to the strength of the acid; salt, 1 1/4 ounces. Mix. Heat the tin hot over a stove, then, with a sponge apply the mixture, then wash off directly with clean water. Dry the tin, and varnish with demar varnish.
(3) Crystallized tinplates are usually prepared from well-annealed and well-tinned charcoal iron plates, rinsing the plates with dilute nitric or nitro-muriatic acid, and then with water. The cleansed plates are dipped for a few moments into nitric acid or aqua-regia (nitric acid 1. muriatic acid 3), diluted with from one to three volumes of water heated to about 180 degrees Fah., and after a moment's exposure to this bath removed and rinsed in running water. This is repeated if necessary, until the crystals are properly developed, when the plate is finally rinsed in hot water, which causes it to dry quickly without rubbing. The plates are then oiled or lacquered to preserve them. Plates which have been heavily rolled or too quickly chilled after tinning, do not afford a good crystallized surface. Hot tannin or strong caustic soda solutions can also be used to develop the crystalline structure of tinplates.