Tinning, is the process of coating copper vessels, chiefly used for culinary purposes : it is generally performed in the following manner :
If the copper be new, its surface is first scoured with salt and diluted sulphuric acid: next, pulverized resin is strewed over the interior part of the vessel; into which, after heating it to a considerable degree, melted tin is carefully poured, and a roll of hard-twisted flax is passed briskly over the sides and bottom, to render the coating uniform. For tinning old vessels, a second time, the surface is first scraped, or scoured with iron-scales, then pulverized sal-ammoniac is strewed over it, and the melted tin is rubbed on the surface with a solid piece of sal-ammoniac. The process for covering iron vessels with tin, corresponds with that last described ; but they ought to be previously cleaned with the muriatic acid, instead of being scraped or scoured only acquire additional strength, but are also secured against the action of acids, for a longer period than is effected by the common methods of tinning : Let the utensil be cleaned in the usual manner; its inner surface be beaten on a rough anvil, that the tinning may more closely adhere to the copper; and let one coat of pure tin be laid on with sal-ammoniac, as above directed in the process for tinning old copper. A second coat, consisting of two parts of tin, and three of zinc, must next be uniformly applied with sal-ammoniac, in a similar manner: the surface is now to be beaten; scoured with chalk and water; smoothened with a proper hammer; exposed to a moderate heat; and, lastly, dipped in melted tin: by which, means both sides will be tinned at the same time. - Such tinning is stated to be very durable, and to have a permanent beautiful colour, so that it may be advantageously used for various metal utensils and instruments, which may thus be effectually prevented, from rust.
Lastly, as many families living at a distance from towns, either have no opportunity of sending their copper utensils to be re-tinned; or carelessly overlook such necessary repair, we think it useful to observe, that the whole process may be easily performed by servants, who possess common skill and dexterity. For this purpose, the vessel ought to be previously scoured, and dried; then exposed to a moderate heat, with such a portion of pure grain-tin as may be sufficient to cover the inner surface: when this metal is melted, a small quantity of sal-ammoniac should be strewed over it ; and, immediately after, a whisk or roll of coarse and hard twisted flax must be employed, for spreading the composition uniformly over the sides and bottom of the vessel. To improve the coating, about a third part of zinc may be added to the tin ; though the latter would produce the desired effect, if it could be obtained in a pure state.