Plating
The Encyclopedia of Founding (1892)
Important: Safety Warning
This page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
The coating of one metal with another. This is done in some cases to protect the underlying metal from oxidation; in others, that the properties of two metals, such as strength and lustre, may be combined in one object; but in the majority of cases it is done that some inferior metal may appear like a superior one. Originally, silver-plate was made by wiring thin plates of silver to ingots of German-silver or copper, and submitting to a soldering temperature in a plating-furnace to unite the two surfaces. The ingot was then rolled down to a sheet, in which the relative thickness of the two metals was maintained. This method of plating has now become almost extinct, being superseded by electro-plating and gilding, which covers the object with a film by the aid of electricity. To coat articles with silver, a bath is made of cyanide of silver 1 part, to 2 or 3 parts of cyanide of potassium, dissolved in 150 parts of water. The article to be plated is made the negative pole, and a piece of silver hung in the bath forms the positive pole. Articles are gilded by employing a solution of the double cyanide of gold and potassium, and suspending plates of gold in the solution. A proper coating takes from three to six hours, but any thickness may be given by continuing the operation. From 1/2 to 1 ounce of silver suffices for one square foot of plating. Other metals besides copper, silver, and gold can be electrically deposited from their solutions, as, for instance, the coating of iron with zinc, a solution of the sulphate of zinc being employed for that purpose. The deposition of nickel from the sulphate of nickel and ammonium is deposited as a very thin but extremely hard coating by this process, so that innumerable articles may be protected from tarnishing and corrosion, as nickel will not readily tarnish, even in a very moist atmosphere. See ELECTRO-PLATING; NICKEL-PLATING; GILDING. Platinum is a rare metal, invariably found native, and usually associated with palladium, iridium, and rhodium. It occurs also alloyed with gold, copper, iron, and lead. Found chiefly in the mines of the Ural Mountains, Brazil, and Mexico. Its color is grayish white, almost like silver in appearance. It is ductile, takes a good polish, and is as malleable as gold or silver. Its most useful qualities, however, are the difficulty of fusion and its absolute resistance to the action of almost all acids; but it may be slowly dissolved by aqua regia. It will not oxidize in air at any temperature. Its specific gravity is 21.5. Platinum with steel forms an alloy that is exceedingly hard. See METALS, AQUA REGIA; PLATINUM ALLOYS.
What Has Changed in the Last Century
When this was written in 1892, electroplating meant essentially silver, gold, nickel and zinc from cyanide or sulphate baths — and the writer was right that the old fire-welded "silver-plate" of soldered sheet was dying out. The great absence is chromium: bright and hard chromium plating only became a commercial process in the mid-1920s, and it, not nickel, became the standard finish on car trim, taps and tools. Electroless nickel plating, which needs no current at all, was developed in the 1940s and now coats everything from oil-field valves to hard-disk substrates, while vacuum and sputter coatings cover plastics that could never have been hung in a bath. Cyanide baths are still used in the trade, but under permit and ventilation regimes, and hexavalent-chromium plating is now sharply restricted in Europe and elsewhere on health grounds. The appended note on platinum has also dated: the Ural, Brazilian and Mexican sources named here were overtaken after the Merensky Reef in South Africa was identified in the 1920s, and most platinum today goes into catalytic converters rather than laboratory ware.
Written for this edition, 2026.