PLATING signifies the covering of an inferior metal with one of the precious metals, the object being to give the appearance of silver or gold to articles chiefly intended for table use. At present the articles are generally made of German silver, or some of the similar white-metal alloys; but formerly, copper, or an alloy of that metal with brass, was used; the disadvantage of which was that, as the coating of silver wore off, the red color of the copper became disagreeably apparent through the thin covering of silver. Gold is rarely plated on any other metal than silver, except for purposes of deception. Previous to the introduction of electroplating, the method generally pur sued was that which has acquired the name of SbeXield-plating, from the large extent to which it was carried on in that town. It consists in soldering on to one or both sides of an ingot of the baser metal a thin plate of silver. The ingot is always of an oblong shape, and is most carefully prepared•on the surfaces which are to receive the silver, so that nothing shall prevent the complete union of the two. The soldering is a process requiring much care and nicety; the plates of silver are thinly coated with a concen trated solution of borax, and are then applied to the prepared surfaces of the ingot, to which they are thinly bound with iron wire, and then placed in the platingfurnace, and subjected to a strong heat. This furnace is so arranged that the interior can be con stantly watched, and when the proper temperature is attained the workman knows the exact instant to withdraw it. The act of soldering is almost instantaneous, and fusion would immediately follow if the ingot was not quickly withdrawn. When cooled, the' wire is taken off, and the ingot is taken to thewhere it is passed backwards and forwards, of course with the silver -above below, until it is rolled out into a sheet of the exact thickness required. However• thin it may be made, it is found that
the relative thickness between the ingot and its layers of silver is always the same.. As usual in all cases of rolling or striking 'metal, annealing from time to time is necessary, to remove the brittleness which these operations cause.
This method does not admit of the manufacture of any portions such as ornamental' molded borders, etc.; these had, therefore, to be formed separately of copper, aid were coated by the process called silvering (q.v.). Now, however, it is found better to make them of silver'rolled thin, and fill them inside with lead, to give them solidity; by this plan is avoided the annoyance of the silver rubbing off, and'exposing the copper. Shef field-plating is still made extensively, but the manufacture is rapidly declining in pres ence of the newer art of electroplating. See GALVANISM.
Within a very recent period, and since the subject of electro-plating was treated under the article GALVANISM, some very remarkable applications of the process have' been discovered; for instance, it is no longer confined to the deposit of silver and gold; aluminium, silicium, titanium, tungsten, molybdenum, tin, cadmium, lead, bismuth, palladium, rhodium, iridium, and the alloys, brass and bronze, are all now deposited under patent procesks. Of all these, by far the most important is the deposit of the alloys, and a very large trade has sprung up in manufactures of iron coated with brass. The importance of being able to cover a metal so cheap, yet so easily corroded as cast iron, with so ornamental an alloy as brass or bronze, can hardly be overrated. Conse quently the process is carried on very extensively and satisfactorily.