The
heated iron is thus forced by the blows to assume the form of the
mould into which it is impressed.
124. Engraving by pressure. This is one of the most beautiful
examples of the art of copying carried to an almost unlimited
extent; and the delicacy with which it can be executed, and the
precision with which the finest traces of the graving tool can be
transferred from steel to copper, or even from hard steel to soft
steel, is most unexpected. We are indebted to Mr Perkins for most
of the contrivances which have brought this art at once almost to
perfection. An engraving is first made upon soft steel, which is
hardened by a peculiar process without in the least injuring its
delicacy. A cylinder of soft steel, pressed with great force
against the hardened steel engraving, is now made to roll very
slowly backward and forward over it, thus receiving the design,
but in relief. The cylinder is in its turn hardened without
injury., and if it be slowly rolled to and fro with strong
pressure on successive plates of copper, it will imprint on a
thousand of them a perfect facsimile of the original steel
engraving from which it was made.
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