STEREOTYPING. The invention of stereotyping has usually been attributed in Europe to W. Ged, of Edinburgh, about 1780: but there is evidence on re cord that in 1779 Cadwallader Colden, of New-York, communicated the plan of the art to Dr. Franklin, then in Paris, and the details were by him given to Didot, the great printer. In 1780, Til losh and Foulis introduced improve ments: a little later, various novelties were added in France under the name of polytype. In some of them the form was imitated by striking upon a mass of soft metal like clichee moulds. Stereo typing, as now practised, became fully established in 1800. (See " World's Progress," p. 543.) Stereotype printing signifies printing by fixed types, or by a cast typographic pate. This plate is made as follows ;— The form composed in ordinary types, and containing one, two, three, or more pages, inversely as the size of the book, being laid flat upon a slab, with the let ters looking upwards, the faces of the types are brushed over with oil, or prefer sky with plumbago (black lead). A heavy iron rectangular frame, with bevelled borders, adapted exactly to the size of the pages, is then laid down upon the chase, to circumscribe its typography. The frame resembles that of a picture, and serves to define the area and thick ness of the cast, which is made by pour ing the pap of Paris plaster into its in terior space, up to a given line on its edges. The plaster mould, which soon sets, or becomes concrete, is lifted gently off the types by the untwisting of a screw at each corner, and immediately placed horizontally on shelves in an oven heated to when they become per fectly dry, in two hours. As they are now friable and porous, they require to be delicately handled. Each mould, con taining generally two pages octavo, is laid, with the impression downwards, upon a flat cast-iron plate, called the float ing-plate ; this plate being itself laid on the bottom of the dipping-pan, which is a cast-iron square tray, with its upright edges sloping outwards. A cast-iron lid is applied to the dipping-pan, which has its corners cut of to allow the melted metal to flow in, and is then secured in its place. The pan having been heated to 4000, by resting on the melted metal, previous to receiving the hot mould, is ready to he plunged into the bath of melted alloy contained in an iron pot placed over a furnace, and it is dipped with a slight deviation from the horizon tal plane, in order to facilitate the escape of the air. As there is a minute space between the back or top surface of the mould and the lid of the dipping-pan, the liquid metal, on entering into the pan through the orifices in its corners, floats up the plaster along with the iron plate on which it had been laid, thence called the floating-plate, whereby it flows freely into every line of the mould, through notches cut in its edge, and forms a layer or lamina upon its face, of a thickness corresponding to the depth of the border. Only a thin metal film is
left upon the back of the mould. The dipping-pan is suspended, plunged, and removed, by means of a powerful crane, susceptible of vertical and horizontal mo tions in all directions. When lifted out of the bath, it is set in a water-cistern, upon bearers so placed as to allow its bottom only to touch the surface. Thus the metal first concretes below, while, by remaining fluid above, it continues to impart hydrostatic pressure during the shrinkage attendant upon refrigera tion. As it thus progressively contracts in volume, more melted metal is fed into the corners of the pan by a ladle, in or der to keep up the hydrostatic pressure upon the mould, and to secure a perfect impression, as well as a solid cast. Were thepan more slowly and equably cooled, by being left in the air, the thin film of metal upon the back of the in verted plaster cake would be apt to so lidify first, and intercept the hydrostatic action indispensable to the purpose of filling all the lines in its face. The lid of the pan being taken off, the compound cake of mould and metal is removed, and beat upon its edges with an iron sledge, to detach the superfluous metal. The stereotype plate is then washed with a brush and water to remove the ad hering plaster, and handed over to the picker, who planes its edges truly square, turns its back flat upon a lathe, in which a steel cutter or knife, mounted on a slide rest, shaves off the metal in concentric circles to a determinate thick ness, and carefully removes the little imperfections occasioned by dirt or air left among the letters when the mould was cast. Should any of them be da maged in the course of the operation, they must be cut out, and replaced by soldering in separate types of the same size and form.
They are then mounted on blocks of wood to the height of type.
In this country a machine, similar to that given in this illustration, is used for smoothing the hack of the plate. This Stereotype Shaving, or Planing Ma chine, for equallizing the thickness of stereotype plates, is made of wrought and cast iron, and rests upon a wooden bench. It consists of a cast-iron bed plate planed perfectly true on the face and edges, with bearings projecting above to receive a wrought iron shaft with two case hardened pinions on it, between the bearings and a hand wind lass, with arms outside, on one end. A sliding head, with knife attached, which can be adjusted by set screws, has two racks attached, by which it is impelled by the windlass and pinions back and forward over the stereotype plate (which is placed on the bed) until it is reduced to the required thickness.