The Matrix. There are three different methods of making type matrices. By the oldest method the first step is to cut the character on the end of a small bar of soft steel, called a punch; when this is done, the steel is hardened and it is used to stamp an impression in a bar of copper. This copper bar is a matrix in the rough, and its sides are next trimmed and squared so that it will fit the mold.
The second method of making a matrix is by electrotype process. The original pattern of the letter may be engraved by hand or by other operation, or it may be a perfect type-face of a previous casting. This is fitted into a small frame of brass and then held in the vat of an electro-galvanic battery, which deposits a thick film of copper around the pattern and fills the opening in the brass frame. When this electro-plating process is completed, the pattern letter is extracted and the brass frame, with its copper impression of the letter, becomes the essential feature of the matrix. It is then reinforced by riveting another plate on the back, and is trimmed and fitted to place on the mold.
A third process of making matrices is with an automatic matrix-cutting machine, in which the shape of the desired letter is cut in the face of a plate of composition metal by a small rapidly-revolving cutting point. A large pattern of the letter is placed in one part of the machine, and while the operator traces the outline with the point of a lever all the motions are duplicated in miniature by the cutting tool on the bar of metal, which becomes, when completed, a matrix.
Casting the Type. The old-time method of casting type was with hand molds, the melted metal being poured in at the foot of the mold with a small ladle while the mold was held in the hand. In the modern casting machine, the mold with its matrix, is assembled by the side of the metal pot, in which the metal is kept at a uniform temperature by means of a gas furnace.
In the center of this metal pot is a rod with a spring attachment which, at each operation of the machine, acts as a plunger to force a small stream of hot metal through a side aperture into the jet-hole of the mold. After the casting, the two parts of the mold separate slightly, the matrix is drawn away from the face of the type, and the cast is moved out; then the mold and matrix close together again and the operation is repeated. Cold water or air is circulated near the mold to keep an even temperature. The matrix for one character only is placed in the machine and when enough types have been cast, it is taken out and replaced by another, the change usually requiring but a few moments.
There are several kinds of type-casting machines in use, such as hand casters, steam casters, and automatic casters. The older style is the hand caster, which is operated by a small wheel with a handle attached. Steam casters are operated by mechanical power (originally steam power).