Electrotype

a copy, usually in copper, of a form of type. A page of the type is covered with wax, which is driven into the interstices by powerful pre ure, The face of the wax mold is covered with plumbago to give it a conducting surface to which the metal will adhere. The positive pole of a battery is attached to the mold, and the negative to a copper plate, and both are plunged into a bath of sulphate of copper in solution. The copper is deposited on the face of the mold in a thin film, which increases in thickne as the proce continues. The shell having attained the thickne of a stout sheet of paper, the mold is removed from the bath, the shell detached and strengthened by a backiftg of type-metal. This proce is called backing-up. As type-metal will not readily adhere to copper, the back of the shell "is coated with tin, and the shell is then placed face downward on a plate, by which it is suspended over a bath of molten type-metal. When it has attained the requisite heat, a quantity of the metal is dipped up and floated over the back of the shell. When cold, the plate is reduced to an even thickne by a planing-machine. For printing, it is mounted on a wooden backing. Another mode of obtaining electrotype plates from a letter-pre form is by a mold of gutta perch a, brushed with graphite and immersed in the electro-plating bath. Gutta-perch a is also used for obtaining intaglio molds and then cameo impre ions from woodcuts, for printing.