As the
metals shrink in cooling, the pattern is made larger than the
intended copy; and in extricating it from the sand in which it is
moulded, some little difference will occur in the size of the
cavity which it leaves. In smaller works where accuracy is more
requisite, and where few or no after operations are to be
performed, a mould of metal is employed which has been formed
with considerable care. Thus, in casting bullets, which ought to
be perfectly spherical and smooth, an iron instrument is used, in
which a cavity has been cut and carefully ground; and, in order
to obviate the contraction in cooling, a jet is left which may
supply the deficiency of metal arising from that cause, and which
is afterwards cut off. The leaden toys for children are cast in
brass moulds which open, and in which have been graved or
chiselled the figures intended to be produced.
107. A very beautiful mode of representing small branches of
the most delicate vegetable productions in bronze has been
employed by Mr Chantrey. A small strip of a fir-tree, a branch of
holly, a curled leaf of broccoli, or any other vegetable
production, is suspended by one end in a small cylinder of paper
which is placed for support within a similarly formed tin case.
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