The art of tinning, or of coating other metals with a thin layer of tin, so as to pro tect them from oxidation, was known to the ancients, although it does not appear to have been very extensively practised. The tinning of plate-iron is more modern than that of copper vessels, and is snpposed to have been invented either in Bohemia or in Germany, whence it spread to France about 1725, and to England about 1730.
The process of tinning depends upon the strong affinity which exists between tin and the metals to which it is applied. The finest bar-iron, called tin-iron, is used for making tin-plates. This material is first made into flat bars, or slabs, about thirty inches long, six inches wide, and weighing eighty pounds ; and these bars are rolled until the metal assumes the proper degree of thinness, after which the sheets are cut into pieces measuring usually about thirteen inches by ten.
The removal of every particle of oxide or other impurity from the surface of the plates is then effected by the application of muriatic acid and of heat ; and any warping is removed by a process of cold-rolling between very hard rollers. The plates are then immersed singly, in a vertical position, in a fermented steep of bran; whence, after 10 or 12 hours, they are transferred to a leaden vessel containing dilu ted sulphuric acid. They are then removed into pure water, in which they are scoured with hemp and sand, to remove any remaining oxide. They are next dried by rubbing with bran, greased on both surfaces, and plunged into the metallic bath, which contains a mix ture of block and grain-tin, covered with a quantity of grease sufficient to form a layer four inches deep, and heated. When the plates have remained in the tin bath an hour or two, they are lifted out with tongs, and placed upon an iron grating, to allow the superfluous tin to drain off; but as there still remains upon them much more than the proper quantity of tin, they are afterwards subjected to a process called washing, which consists in dipping them into a pot containing a quantity of pure grain-tin in a melted state, then rubbing them' with a peculiar kind of brush made of hemp, plunging them again for a moment into the melted tin in the wash-pot, and then into a pot filled with clean melted tallow, orlard free from salt. Owing to the ver tical position of the plates during the preceding operations, a selvage of tin accumulates along their lower edge, which is partially removed by a re-melting and shaking of the edge. The plates are then cleaned from grease by rubbing them, while yet warm, with ,dry bran ; after which they are packed in boxes of wood or sheet-iron.
The tinning of the inner surfaces of cook ing utensils and other vessels of capacity is formed by scouring the surface until it is perfectly bright and clean; then heating the vessel, pouring in some melted tin and rolling it about, and rubbing the tin all over the surface with a piece of cloth or a handful of tow : powdered rosin is used to prevent the formation of oxide. Bridle-bits, stirrups, and many other small articles, are tinned by im mersing them in fluid tin.
Tin-Plate Working, or the forming sheets of tinned iron into a variety of useful vessels and utensils, is carried on by means of bench and band-shears, mallets and hammers, steel heads and wooden blocks, soldering-irons and swages. In the formation of a vessel the
first operation is to cut the plate to the proper size and form with shears ; and when the dimensions of the article require it, to join them together, which is done either by simply laying the edge of one plate over that of the other, and then soldering them together, or by folding the edges together with laps, and then soldering them. Similar joints are re quired when gores or other pieces are to be inserted, and also at the junction by which a cylinder is closed in. The usual method of forming laps, bends, or folds for this or other purposes is to lay the plate over the edge of the bench, and to bend it by repeated strokes with a hammer ; but a machine is sometimes used for this purpose.
After a tin vessel has been rounded upon a block or mandril, by striking it with a wooden mallet, and the seams finished, all its exterior edges are strengthened by bending a thick iron wire into the proper form, applying it to what would otherwise be the raw edges of the metal, and dexterously folding them over it with a hammer. A superior kind of tin-ware, commonly known as block-tin ware, is carefully finished by beating or planishing with a polished steel hammer upon a metal stake. The process of swaging is resorted to as a ready means of producing grooved or ridged borders or other embossed ornaments. This process consists in striking the metal between two steel dies, or swages, the faces of which bear the desired pattern, and are made counterparts to each other. Many ornamental articles are produced by embossing or stamp ing tin-plate, in the same manner as other metallic sheets, with a fly-press or other machinery. Cheap coffin-plates are manufac tured at Birmingham in this way ; and these and similar articles are sometimes lacquered, painted, or japanned. One particular kind of tin plate is described under Mort.
Tin forms the principal ingredient in various kinds of pewter and other white metallic alloys, which are manufactured into domestic utensils by casting, stamping, and other processes. Britannia Metal is a mixture of tin, antimony, copper, and brass ; which is melted, cast into slabs, and rolled into sheets. The principal use of this metal is for candle sticks, tea-pots, coffee-biggins, and other vessels for containing liquids. The feet of candlesticks, the bodies of tea-pots, and other articles containing embossed work, are stamped between dies ; while articles of a more globular shape are stamped in two or more pieces, which are afterwards soldered together. The sheet metal has a ductility which enables it to be bent into various curved forms, by pressure on a model or core : this process is called spinning.
Many small vessels, spoons, and other articles, are cast in an alloy somewhat harder than that which is rolled into sheets. Articles of this metal are cleaned from the oil, resin, and other impurities acquired during their formation, by boiling in water containing sweet soap ; after which they are polished, either by hand, or more commonly by the buff and brush set in motion by 4 steam engine ; then boiled in a solution of pearlash ; and finally hand-brushed and hand-polished by an application of soft soap, a little oil, and powdered rotten-stone.