Matrices for stamp moulds can be made by several of the methods used by stereotypers. Thus an electrotype could be taken directly from the face of the type. There would be little or no utility in doing this where the simpler processes are available.
The stereotyper for daily newspaper work uses very generally the papier maché or “flong” process of reproducing the page. This is also available for rubber stamp making.
The first requirement is paste. This is made by softening twelve parts of whiting in forty parts of water, letting it soak for an hour or more. Nine parts of wheat flour are added. This is best mixed with a little water before adding to the main mixture. It is then brought to the boil and seven parts of glue softened by soaking in twenty-one parts of water, are added. For each gallon of such mixture, one ounce of white crystallized carbolic acid is added if it is to be kept for a long time.
The “flong” is made by pasting together, one on top of the other, a sheet of fine hard tissue paper, three sheets of blotting paper (about 23 pounds to the ream), and a heavy sheet of manilla paper. The pasting must be smooth and each layer must be pressed and rubbed down, but not too hard. It is very important to secure perfect smoothness and regularity, and entire absence of air bubbles.
Every printing office where the process is used has its own traditions as to the preparation of flong. As a great deal depends on manipulation, it would be well to endeavor to inspect its practical use in a newspaper printing office before making it. Ready prepared flong can also be procured.
The form of type must be very clean and there must be no paste on the tissue paper face of the flong. The type are lightly oiled, some powdered talc is dusted over the damp tissue paper face of the flong, and the mass is laid face downward on the type. With a stiff haired brush the paper is now beaten down against the type. Great care must be taken to beat vertically; a slight side action will ruin the resulting matrix. If the brown paper will not stand the beating, a cloth may be spread over it.
The progress of the work can be watched by raising up a corner from time to time. When sufficiently deep the last touch is given by the printer’s planer. This is a block of hard wood. It is placed upon the back of the flong and is hammered down. The operation is repeated until the entire area has been treated. For much rubber stamp work the area would be so restricted that shifting would be unnecessary.
The work is then put into a heated screw press, such as the vulcanizing and matrix press, and is dried for a period varying from some minutes up to half an hour. Some blotting paper is advantageously pressed on top of the whole in the press while drying. The press is opened, the flong removed, and dried in an oven. It is kept under a piece of wire net while drying to keep it flat. The net may be of wire, .064 inch thick, with six meshes to the inch. This baking is not strictly necessary for rubber stamp work.
This gives a matrix which may be used as rubber stamp moulds. In use it is recommended to place a piece of smooth tin foil over it. This tends to give a smoother surface to the rubber.
Didot’s polytype process may be advantageously used for producing type metal matrices. The following is the method of applying it.
The type form is firmly locked and is backed up by and secured to a solid block of wood. It is suspended in a sort of gallows frame with the face of the type downward and exactly level a few inches above a table. Underneath it a shallow tray is placed, into which some melted type metal is poured. The melted metal is carefully watched. The block and type are held by a catch so as to be released at will. Just as the type metal is on the point of solidifying, the block is released and drops upon the metal in the tray. The type should be slightly oiled. The force of the blow produces a matrix in the metal, and the form can at once be removed.
It is well to have accurately adjusted distance pieces for corresponding striking pieces on the type block to impinge upon. The process is highly spoken of, especially for small forms such as those mostly required for rubber stamps.
The base for this form of matrix is a metal plate whose surface is slightly roughened with sand-paper. It is next rubbed over with white of egg, and flooded with the chalk wash made as follows: Flong paste (described under Papier Maché Matrices, page 80), six ounces; whiting, twenty-four ounces; water, three pints. The whiting is softened by soaking for an hour or more. The whole must be intimately mixed. It should cover the plate to the depth of one-thirtieth to one-twentieth of an inch. The plate is dried in a perfectly horizontal position.
When dry the design or writing, etc., is made with a smooth steel point, the lines being carried clear through the white layer to the metal. The mould is now baked at a temperature well above boiling water; as high as 392° F. (200° C.) may be reached without harm.
If the coating seems too thin, an extra coat can be given between the lines especially over the larger areas. This must be done before the baking. A pipette may be used for putting on this coat. This deepening has the bad effect of increasing the chance of the coating stripping from the metal.
The matrix thus prepared is used in the press just as is the ordinary plaster matrix. It is suited for reproduction of autographs, scrip, diagrams, etc.