Electrotype

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Electrotype is a metal printing plate made by an electroplating process. It provides an exact duplicate of an engraving or of a page of original type. Electrotypes were once widely used to print magazines, books, and catalogs. They weren't used to print newspapers because they couldn't be made quickly enough to meet newspaper printing schedules.

Advantages of Electrotypes

One of the most important advantages of electrotyping is that many electrotypes can be made from the same original type. Electrotypes produce printing of excellent quality, and they are therefore used to print currency. Moreover, ordinary type cannot be used on the highspeed rotary presses used to print many magazines, because the presses require curved plates. It is fairly easy, however, to make curved electrotypes for rotary presses.

Making an Electrotype

The first step in producing an electrotype is to make a mold of the original type. Molds are usually made of plastic, vinyl, or beeswax. For fine work, sheet lead is used to make the mold. Molds made of plastic and other electrically non-conductive materials are made conductive by spraying a thin film of silver on the mold.

The mold is placed in an electrolytic bath that contains a copper salt, and it is connected to the negative terminal of a direct-current power supply. When current is sent through the bath, a copper shell is plated onto the mold by electrolytic deposition.

Most copper shells are about 0.006 of an inch (0.15 millimeters) thick. If the plate is to be used for a long printing run, a nickel and copper shell is made with a layer of nickel about 0.001 of an inch (0.03 millimeters) plated onto the mold before the layer of copper is deposited over it. Some especially long-lasting electrotypes have a thin layer of chromium plated over the copper. Chromium-plated electrotypes can make as many as one million impressions.

After the mold has been plated to the desired thickness, it is removed from the electrolytic bath and separated from the metal shell. A molten lead alloy is then poured onto the nonprinting side of the plate to give it strength. Finished electrotypes vary in thickness from 0.105 of an inch (2.7 millimeters) for newspaper advertising plates to 0.250 of an inch (6.4 millimeters) for curved press plates. Some electrotypes are mounted on wooden blocks to raise them to the proper height.   

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