A variety of machines are used in perforating stamps. One perforates only a single row of holes at a time. This is known as the guillotine machine because its action suggests that unpleasant instrument. Another machine is called the comb machine because the needles are arranged to perforate across the top of a row of stamps and at the same time between the stamps of that row. This arrangement somewhat resembles a comb. It will be seen that the first application perforates the stamps of one row on three sides. The application of the machine to the next row below completes the fourth side. In the best perforating machines the needles are arranged in circles around a spindle. The sheets pass under this roller and are perforated in one direction. A similar machine makes the perforations in the other direction.
There is another form of separation called rouletting, from the French "roulette", a little wheel, its simplest form being produced by a small wheel with an edge of sharp points. By this process a series of small cuts is made between the stamps but none of the paper is removed.
In these two illustrations are shown roulettes of large and small gauge. The same result is also obtained by setting printers rules which have a notched edge between the clichés which compose the plate. These rules are set a trifle higher than the clichés so that, when the sheet of paper is pressed against the plate in printing, the points of the rules are forced through it. These points receive ink the same as other parts of the surface of the plate and the effect thus produced is called rouletting in colored lines.
There are a number of systems which produce the effect of rouletting in a variety of fancy forms. One is called percé en arc. This produces a series of arches on one stamp and a series of scallops on the adjacent one. Here is an example of this rouletting, in a small gauge. A similar form is called serpentine perforation. It is here shown.
