Place the press on a
support over a gas burner; or a kerosene lamp, and apply the heat.
Place the matrix on the base of the press, dust off the piece of
india rubber and place in the press upon the matrix and screw down
the platen. Heat the press to 284 deg. F. and keep screwing down
the platen so that the rubber, now soft and putty-like, is forced
into every recess of the matrix. A thermometer is not necessary;
some rubber always protrudes and the stage of the process can be
told from that. At first it is quite elastic, then as the heat
increases it becomes soft, then the curing begins and it again
becomes elastic, so that, if a point of a knife blade is pressed
against it, it resumes its shape when the point is removed. When
this takes place it is then thoroughly vulcanized and the sheet
can be removed from the matrix. Ten minutes, under favorable
conditions, is sufficient time for moulding the rubber. By means
of common glue, or bicycle tire cement, fasten the rubber stamp to
a wooden handle.
It is possible to dispense with the press in making stamps, where
the work is not done in quantities, and use a hot flat-iron.
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