stamps.

Until the early part of the present century copper was practically the
only metal used for engraving. Only a limited number of impressions can
be taken from a copper plate because it wears rapidly, and it is not
suited to such work as the production of postage stamps. About 1830 the
way was found to make steel of sufficient softness and fineness of grain
to be available for engraving. To-day annealed steel is almost
exclusively used for this purpose. Annealed steel is steel which has
been softened without being decarbonized. The surface is carefully
ground and polished to a mirror-like brightness. Any work which is to be
reproduced many times, such as postage stamps and parts of bank-notes,
is made on small pies of steel called dies.

If the design to be used is in the shape of a drawing or engraving, a
sheet of gelatin may be laid over it and the outlines traced with a
sharp-pointed instrument. More often a photograph is taken on a
ferrotype plate and the outlines scratched into the plate. These
outlines are filled with vermilion. A piece of paper is then laid on the
plate and the two passed through a hand-press. This is called "pulling"
an impression. While the ink of the impression is still moist it is
sprinkled with powdered vermilion to strengthen the lines. The block of
steel is then covered with an etching ground (a composition of
asphaltum, wax, resin and ether) and the impression is transferred to
this. The outlines are cut through the etching ground and bitten into
the steel with acid. The coating is then removed from the block and the
artist proceeds with the engraving. The mechanical details and various
methods of engraving are highly interesting but time will not permit
their discussion.