SILVERING. A few illustrations of the mechanical working of silver will be found under BIRMINGHAM, ELEOTRO-METALLURGY, and GOLD-WORKING ; but we are here speak ing of the singular operation of silvering one surface of glass.
In an ordinary looking-glass, the reflexion is derived from a film of mercury or quick silver, in contact with the hinder surface of the glass, and rendered fixed by amalgama ting with a sheet of tin foil. Silvering is hero not a correct term, for there is no silver em ployed; the process is nevertheless a highly curious one. In the first place a large sheet of tin foil is unrolled, and laid down on a perfectly flat and very smooth stone table. Liquid mercury is poured on the foil, from the iron bottles in which it is imported, and made to float over the entire surface. The glass, brought perfectly elean, is laid upon the mercury with a peculiar sliding movement, which suffices to remove the slight film of oxide which soon• forms upon the surface. The glass is then entirely covered with heavy leaden weights, which could not be done with safety unless the. glass and -the stone were perfectly flat. After remaining a day or two in this 'state, with the stone slightly inclined, it is found that all the superfluous mercury has been pressed out from between the glass and the foil; and moreover the mercury has chemically combined -with the foil, in'such a way that both adhere firmly to the back of the glass. So great is the tact shewn in this process that in a well silvered there will not be found the smallest spot which has not its due share of reflective amalgam behind it.
Mr. Drayton patented a new mode of , silvering glass, a few years ago. It is not only'nominally but really siliering. Nitrate of silver is combined with spirit and certain liquids, and is poured on the clean surface of a the glass ; border -of putty or some other substance being laid round the glass to retain the liquid. After remaining thus a few hours,
the liquid is poured off, and a sediment of silver is found to be left adhering to the -glass. This sediment or film is secured in its place by a varnish of bees' wax and tallow.
• recent novelty is Kidd's Embroidered Glass, by which any pattern or device can 'be embroidered on glass, and thus fixed and rendered conspicuous by a sithiequent silver ing. The peculiarity of the process is that the patterns have the appearance of being in' relief, or embossed on the exterior surface, and illuminated in frosted and burnished silver; whereas the whole of the Processes are effected on the under surface. The en graving or embroidering is effected by pecu liar tools ; a peculiar composition is laid on the embroidered glais before the silver is applied ; and the silver itself is applied in a way different from in any other process.
Another new production is Mr. Thomson's silvered vessels, which display wonderful brilliancy and beauty. Glass vessels of any shape, and made of glass of any colour, are silvered within in such a way as to yield a reflection of' great lustre. Some'of the speci mens in which green and ruby glass are thus silvered produce an effect which for gorge ousness can hardly be paralleled in any other manufacture. The surface is 'often richly cut and diversified; and the silvering may be made to appear at any spots selected by the workman. The silvering agent is one of the salts or compounds of silver, as in Drayton's process ; but arrangements of a novel and intricate kind are 'requisite to the due pro diction of the required effects.
These graceful novelties in the glass manu facture appropriately find a place in the Great E on. ,