Of Copying By Stamping
128. This mode of copying is extensively employed in the
arts. It is generally executed by means of large presses worked
with a screw and heavy flywheel. The materials on which the
copies are impressed are most frequently metals, and the process
is sometimes executed when they are hot, and in one case when the
metal is in a state between solidity and fluidity.
129. Coins and medals. The whole of the coins
which circulate
as money are produced by this mode of copying. The screw presses
are either worked by manual labour, by water, or by steam power.
The mint which was sent a few years since to Calcutta was capable
of coining 200,000 pieces a day. Medals, which usually have their
figures in higher relief than coins, are produced by similar
means; but a single blow is rarely sufficient to bring them to
perfection, and the compression of the metal which arises from
the first blow renders it too hard to receive many subsequent
blows without injury to the die. It is therefore, after being
struck, removed to a furnace, in which it is carefully heated
red-hot and annealed, after which operation it is again placed
between the dies, and receives additional blows. For medals, on
which the figures are very prominent, these processes must be
repeated many times. One of the largest medals hitherto struck
underwent them nearly a hundred times before it was completed.
130. Ornaments for military accoutrements, and furniture.
These are usually of brass, and are stamped up out of solid or
sheet brass by placing it between dies, and allowing a heavy
weight to drop upon the upper die from a height of from five to
fifteen feet.
131. Buttons and nail heads. Buttons embossed with crests or
other devices are produced by the same means; and some of those
which are plain receive their hemispherical form from the dies in
which they are struck. The heads of several kinds of nails which
are portions of spheres, or polyhedrons, are also formed by these
means.
132. Of a process for copying, called in France clichee. This
curious method of copying by stamping is applied to medals, and
in some cases to forming stereotype plates. There exists a range
of temperature previous to the melting point of several of the
alloys of lead, tin, and antimony, in which the compound is
neither solid, nor yet fluid. In this kind of pasty state it is
placed in a box under a die, which descends upon it with
considerable force. The blow drives the metal into the finest
lines of the die, and the coldness of the latter immediately
solidifies the whole mass. A quantity of the half-melted metal is
scattered in all directions by the blow, and is retained by the
sides of the box in which the process is carried on. The work
thus produced is admirable for its sharpness, but has not the
finished form of a piece just leaving the coining-press: the
sides are ragged, and it must be trimmed, and its thickness
equalized in the lathe.