ELECTROTYPING. For tine book work and for duplicating engraved illustrations, electrotyping is the process preferred. By this process the type page is impressed in a thin sheet of wax which is first dusted with a coating of powdered graphite and then with a coating of iron filings. The wax mold so prepared is immersed in a bath solution of sulphate of copper through which passes an electric current from a dynamo. This deposits a thin film of copper on the wax mold. (See ELECTROCHEMISTRY, INDUSTRIAL APPLICATION OF.) When thick enough to be stable the film o• shell of copper is backed with a solder of tin, and afterwards with a firmer basis of type metal, applied in a melted state. This type metal base is then planed and beveled, so that it can he neatly fitted to a thicker base of hard wood that makes it type-high. Electrotype plates may he curved by passing them through shapers or suitable bending rolls. Electrotype plates for printing were made by Joseph A. Adams. a wood engraver of New York City, in 1839-41. but they did not supplement stereotype before 1850.
1:xxixo ROLLERS. Printing ink is a tritura
tion (not a chemical union) of boiled oil, smoke black, coloring matter, and other ingredients. By the old process for inking types, stuffed leather balls were made use of, but they were difficult to keep in proper order, and were inapplicable to cylinder printing. The first improvement on the stuffed balls consisted in covering them with the elastic composition of glue and treacle then em ployed in the Staffordshire potteries. Catching at this idea, the inventors of cylinder printing machines made inking rollers by casting them in a cylindrical mold. This invention came general ly into use between 1814 and 181S, everywhere superseding balls, and rendering printing ma chinery practicable. Inking rollers for type work, now made of a mixture of glue, glucose, sugar, and glycerin, arc found more durable than those made from glue and molasses only. The quantities of each constituent must be varied to suit the speed of the machine, the nature of the presswork, and the temperature of the press room.