The material for moulding is finely ground gypsum, nine parts of which are mixed with about seven parts of water, and well stirred up. A small quantity of the liquid mixture is poured over the pages, and gently pressed into the counter of the types with a small roller, for the purpose of expelling confined air; after which, the remainder of the gypsum is poured in, until the mould is somewhat higher than the upper edge of the flask. In a few minutes the mixture sets, and the upper side is smoothed over with a steel straight-edge. In about ten minutes the mould is gently raised by means of the screws at the corners of the flask; and, after being nicely trimmed at the sides, and nicked on the surface-edges to make openings for the metal to run in, it is placed on a shelf in an oven, and allowed to remain until the moisture has quite evaporated.
The casting-pans may be large enough to hold three or four moulds. The dried moulds are placed in a pan face downward, upon a movable iron plate called a floater. The cover of the casting-pan, which has a hole at each corner for the passage of the metal, is then clamped to it, and lifted by a movable crane and gently lowered into the metal-pot,—containing, it may be, a thousand pounds of liquid metal,—till the metal begins to flow slowly in at the corners. When the pan is filled, it is sunk to the bottom of the pot. The metal should be hot enough to light a piece of brown paper held in it. After being immersed eight or ten minutes, the pan is steadily drawn out by means of the crane, and swung over to the cooling-trough, into which it is lowered and placed upon a stone so as just to touch the water, in order that the metal at the bottom of the pan may cool first. The metal contracts while cooling, and the caster occasionally pours in a small quantity at the corners from a ladle, till it will take no more. It may be here remarked that some stereotypers do not dry the moulds, but immerse them in a green condition into the metal.
The plates are carefully removed from the solid mass which comes out of the pan, and the plaster is washed from the surface. If, after examination, the face is good and sharply set, the plates are passed over to a picker, who removes any slight defects arising from an imperfection of the mould. They are then trimmed and passed through the shaving-machine, till all are brought to an equal thickness. The flanges are neatly side-planed, and the plates are then boxed, ready for the printing-press.
In England, the plates are merely turned on the back, and consequently vary in thickness. This must be a source of continual expense and annoyance to the pressman. The flanges, besides, are very imperfectly made,—so imperfectly that they cannot be used on American printing-blocks; and English plates, when imported into this country, are therefore sent to a foundry here, to be brought to an equal thickness and to be properly side-planed. An order given some years ago by an English printer for a set of American printing-blocks was afterward countermanded, on account of the prejudice against the introduction of new things.
Several methods of stereotyping are now practised. Many of the leading newspapers of England and America are printed from stereotype plates cast in moulds made of prepared paper: this mode, however, yields very inferior plates, quite unfit for fine books.
Another method, styled the “mud-process,” is by spreading a thin coating of pulverized soapstone and gypsum over an iron plate, and a mould is then obtained by pressing the coated face against a page of type. Several of these mould-plates are then set on end in an iron box, separated from one another by a wire of the thickness of the stereotype desired, and hot metal is poured in. This is a very expeditious process, though not so good as the old method.
In 1804, before the introduction of stereotyping into this country, Mathew Carey, the well-known enterprising publisher in Philadelphia, had the Bible in quarto set up entire, and regularly imposed in chases, to print from at convenience, according to the demand for the volume. The type was cast by Binny & Ronaldson. Stereotyping would have saved much of the large outlay required to carry out the scheme, which, nevertheless, even under these circumstances, was doubtless highly remunerative. The weight of type must have amounted to 25,000 pounds, to say nothing of the number of chases and column-rules required.
ELECTROTYPING.
Stereotyping has been superseded by the process of electrotyping, as described below.