Stereotyping (Gr. stereos, 'solid') is the art of fabricating solid casts in type-metal from pages of movable types. Unless when the number required of any printed matter is very small, the actual printing is very seldom executed directly from the types (see PRINTING). When the pages are all corrected and ready for the press casts are taken from them either in type-metal (stereotypes) or in copper (electrotypes). The latter method, being sharper and much more durable, is generally used when large numbers are to be printed, and will be found described in the article ELECTRO-METALLURGY.
Stereotyping being much cheaper, and quite suitable where moderately large numbers are required, has also, in the papier-maché process, the advantage that it can be executed in a very short time—an important matter in connection with newspapers. It was invented by William Ged (q.v.), a goldsmith in Edinburgh, about the year 1725. His process is as follows: after slightly oiling the surface of the types with a soft brush, stucco mixed to the consistency of thick cream is poured over them and allowed to 'set;' the stucco, when taken off and baked in an oven till quite hard, forms a perfect matrix from which a cast in type-metal (see TYPE) is taken by means of a hollow casting-box which dips the mould into the molten metal. The cast, which should be a perfect fac-simile of the types, is finally trimmed, planed on the back down to the required thickness (about inch), and carefully sized to fit the blocks on which it is to be printed. This process was universally employed for all purposes till it began to be superseded by the papier-maché process, invented by Genoux (1829), and introduced into England from the Continent. Its advantages, in cheapness and rapidity, were at once apparent, and now Ged's process is nearly if not quite extinct. The process is as follows: several plies of soft thin paper, very carefully pasted together, are placed in a wet state on the face of the types, beaten in with a hard brush, and impressed as deeply as possible into all the interstices. The hollows on the outside of the paper are filled up with pipeclay or similar material to give solidity to the mould, and a strong piece of brown paper pasted over all. It is then dried on a hot plate till hard enough to be lifted off the types. It is next put into a flat casting-box, the sides of which are, when closed, just far enough apart to allow the cast to be of the required thickness. The metal must be poured in hot enough to run properly, but not hot enough to burn the paper. The cast is then trimmed and made ready for the printing-machine as in Ged's process. Any accidentally bad letters can be replaced by cutting a hole in the plate, and inserting and soldering in a type. Whole lines or sentences can also be altered, the required new pieces being cast separately and soldered into the plate. The papier-maché mould is not destroyed by the casting like the stucco matrix, but can be kept, and, if carefully used, almost any number of casts may be made from it.
It is a modification of this process which has made the printing of newspapers on the rotary printing-machine successful (see PRINTING). In this process, where the stereotype plates are required to be fitted round a cylinder, and great rapidity is necessary, the following changes are made on the method already described. The paper, instead of being beat into the type with a brush, is pressed in with a soft roller, and is then rapidly dried by means of hot blankets in a hot press. When ready the mould is bent inside a cylindrical casting-box, the core of which is exactly of the same diameter as the printing cylinder. The cast when taken out consequently fits the machine exactly. So complete are the stereotyping arrangements in the larger newspaper offices that duplicate casts of a page of the paper can be prepared in ten or twelve minutes. See F. J. F. Wilson, Stereotyping and Electrotyping (3d ed. 1887).