The colour which is given
to glass is, perhaps, the most successful part of the imitation.
A small cylindrical rod of coloured glass is heated in the flame
of a blowpipe, until the extremity becomes soft. The operator
then pinches it between the ends of a pair of nippers, which are
formed of brass, and on one side of which the device intended for
the seal has been carved in relief. When the mould has been well
finished and care is taken in heating the glass properly, the
seals thus produced are not bad imitations; and by this system of
copying they are so multiplied, that the more ordinary kinds are
sold at Birmingham for three pence a dozen.
116. Square glass bottles. The round forms which are usually
given to vessels of glass are readily produced by the expansion
of the air with which they are blown. It is, however, necessary
in many cases to make bottles of a square form, and each capable
of holding exactly the same quantity of fluid. It is also
frequently desirable to have imprinted on them the name of the
maker of the medicine or other liquid they are destined to
contain. A mould of iron, or of copper, is provided of the
intended size, on the inside of which are engraved the names
required.
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