STEREOTYPE. Stereotype Printing is printing from cast plates of type-metal instead of moveable letters or types. It was first adopted by 'William Ged, a goldsmith of Edin burgh, about 1725 ; but his method fell into disuse. About the year 1780, Mr. Tilloch and Mr. Rallis introduced further improvements. Towards the latter end of the 18th century, many projects were brought forward in France for multiplying engraved blocks or forms of type by processes more or less resembling that of stereotyping, under the names of poly type, stereotype, In some of these the form was imitated by striking upon a mass of soft metal, in the way described under CueniE. Some of the early experiments of Senefelder, the inventor of lithography, were directed to the discovery of a means of stereotyping by which he might be enabled to print his own works with a very small stock of type. He formed a composition of clay, fine sand, flour, and pulverised charcoal, mixed with a little water, and kneaded as stiff as possible ; and with this paste he made- a mould from a page of type, which became, in a quarter of an hour, so hard that he could take a very perfect cast from it in melted sealing-wax, by means of a hand-press. He states that, by mixing a little pulverised plaster of paris with the seal ing wax, the stereotype plates thus produced were much harder than the common type metal of lead and antimony. Professor Wil son, of Glasgow, in 1797, devised a method of multiplying engraved blocks or plates by • stereotype or rather polytype impressions in glass or enamel, which, it was anticipated would prove very durable, and might be ap plied with acbiantage to the prevention o forgery. The revival and introduction into common use of the stereotyping process is in a great measure, due to the exertions of the late Earl Stanhope, about the commencement of the present century ; the earl assisted with his counsel and purse many of those who were at that time engaged on the subject; and stereotype printing became firmly established about 1809.
In setting up a form intended for stereo typing from, the spaces, or, short pieces of metal by which the words are separated from each other, and the quadrats, or larger spaces by which blank lines are filled up, are cast higher than usual. The types are set up and formed into pages in the usual manner, with the illustrative wood cuts, if there be any; but instead of these pages being arranged into a form of sufficient size to print a whole sheet, each page, if large, or every two or four pages, if small, is separately locked up in a small frame or chase; the pages being surrounded by fillets of wood or metal, which serve in the cast to form a border for attaching the plate to its mount.. The face of the types is then moistened with oil, to prevent the mould from adhering to them. A brass frame rather
larger than the page is laid upon the chase, in order to retain the plaster while in a fluid state, and to regulate the thickness of the mould. The plaster is then poured on the types, and it soon sets into a solid mass, which must be removed from the types with great care, and trimmed on the edges with a knife. The plaster moulds are, in the next place, baked in an oven heated to about 400° Fahr., until they are thoroughly dry and hard. They are placed upright in a rack, and are usually dried in about two hours. Great care is re quired in this process, especially when the moulds are large, to prevent them from ing.
After being baked, the mould is placed, with its face downwards, upon a smooth plate of iron, called a floating plate, which lies at the bottom of a cast iron box rather larger than the mould. The box is then covered in by a lid, the under surface of which is made per fectly flat, and which has the corners cut off to allow the melted metal to enter the box. The cover is firmly held down by a screw, which is attached to an apparatus by which the box is suspended from a crane. It should be observed that the casting box and plate arc heated to the same temperature as the mould before it is inserted. The box is then swung by the crane over the metal pit, which is an open iron vessel containing a largo quantity of melted metal, resembling in its composition that used for casting types ; and it is lowered into the metal in a nearly hori zontal position, being a very little inclined, to facilitate the escape of air from the mould and box. The melted metal runs in at the corners of the box ; and by its greater specific gravity, floats up the plate with the mould, forcing the latter tightly against the lid of the box. By this contrivance the metal is forced by hydrostatic pressure into every part of the mould, in the margin of which notches are cut to allow free passage for the metal between it and the floating plate. After remaining immersed in the metal for about ten minutes, the box is gently raised, and removed by the crane to a trough in which its lower part is rapidly cooled by contact with cold water. While the box is cooling, the caster pours in a little metal at the corners, to fill the space left by the contraction of the metal, and so to keep up the necessary pressure upon the cast. When cold, the contents of the box are re moved in a mass, from which the superfluous metal is broken off by blows from a mallet. The plaster mould is then broken away from the cast, the face of which is a facsimile of the types and engravings from which the mould was taken. As the mould is destroyed by this process, it is necessary, when several stereotype plates of the same page are re rifted, to take a distinct plaster mould for 3ach.