The _plating_ of copper with silver is a very useful operation, and is thus performed. Plates of silver are bound with iron wire, upon small ingots of copper. The quantity generally allowed is one ounce of silver to twelve ounces of copper. The surface of the plate of silver is made not quite so large as that of the copper; and upon the edges of the copper, which are not covered by the silver, a little borax (204) is put. By exposing the whole to a strong heat, the borax melts; and, in melting, contributes to fuse that part of the silver to which it is contiguous, and to attach it, in that state, to the copper. The ingot, with its silver plate, is then rolled between steel rollers moved by machinery, till it is of proper thickness. It is afterwards cut into such sizes and to such shapes as may be required for use. An ounce of silver is thus often rolled out into a surface of three square feet, having its thickness, upon the copper, not more than the three─thousandth part of an inch. Hence we ought not to be surprised at the silver being soon worn from the sharp edges of plated goods. To prevent this, it is customary, with the best articles, to have all the edges, and the parts liable to be worn, formed, to a considerable thickness, of silver. What is called _French plate_ is made by heating copper, or more frequently, brass, to a certain degree, then applying leaf─silver to the surface, and strongly rubbing it with a burnisher. The durability of this plating depends of course on the number of leaves which are applied on a given surface. For ornaments that are not much used ten leaves may be sufficient; but a hundred will not last long, if the metal be exposed to frequent handling or washing. Besides the above, there are various modes of _silvering_ metal articles, or, as it is called, _washing_ them with silver. All these are performed by different chemical preparations of this metal. The article denominated _shell─silver_, used by painters, is prepared, by carefully grinding silver─leaf, with a little honey or gum water upon a slab, or in a mortar, and separating the honey or gum by means of water. When this is washed away, the silver may be put on paper, or kept in shells, for use. When it is to be used, it must again be diluted with gum water. The application of silver─leaf for the silvering of paper or wood is similar to that of gold─leaf (227).