This method of ornamenting tin goods was at one time very fashionable; but like many other good things it has fallen somewhat into disfavor, probably owing to the "cheap" look given by inferior work. The process consists in various methods of bringing out or displaying the crystalline character of tin. This is effected by first obtaining a good crystallization, and then dissolving, by means of suitable acids, that portion of the metal which has not been crystallized and which seems to have less power of resisting acids than the crystals. The surface may afterwards be varnished or lacquered with plain or colored lacquer, and very beautiful effects produced.
The following is the original process of M. Baget: -
After cleansing away every extraneous matter, as dirt or grease, with warm soapy water, rinse the tin in clean water. Then, after drying it, give it a heat to the temperature of bare sufferance to the hand, and expose it to the vapor of any acid that acts upon tin, or the acid itself may be poured on or laid on with a brush, the granulated crystallization varying according to the strength of the wash and the heat of your plates. Hence, it must be perceived, whatever quantity is required for any particular job of work should be made all at one time, - no two makings coming away alike, but depending entirely upon accident.
Take 1 part by measure of sulphuric acid, and dilute it with five times as much water.
Take of nitric acid and water equal quantities, and keep the two mixtures separate. Then, take of the first 10 parts, and 1 part of the second. Mix, and apply the same with a pencil or sponge to the surface of the heated tin, repeating the same several times, until the material acted upon loses its heat, or you may be satisfied with the appearance of your work. A transparent varnish is now to be laid on, much whereof will be absorbed, and will of course be affected by any coloring matters you may mix with it. These, however, should not be opaque colors; and a good polish being given to the work produces that enviably brilliant material we find so much in use.
Another formula which is said to give excellent results is as follows: -
The plate-iron to be tinned is dipped into a tin bath composed of 200 parts of pure tin, 3 parts of copper, and 1 part of arsenic. Thus tinned, the sheet-iron is then submitted to the seven following operations: -
1. Immersing in lye of caustic potassa, and washing.
2. Immersing in aqua regia, and washing.
3. Immersing in lye of caustic potassa, and washing.
4. Quickly passing through nitric acid, and washing.
5. Immersing in lye of caustic potassa, and washing.
6. Immersing in aqua regia, and washing.
7. Immersing in lye of caustic potassa, and washing.
Every time that the sheet-iron is placed in aqua regia the oxide of tin thereby produced must be entirely removed, since otherwise spots would form. The quickly passing through nitric acid softens the unpleasant metallic glare which, at certain angles of refraction, renders the design invisible. The copal resins deserve the preference for coating the sheet-iron after the ci'ystallization has been thus obtained.