Bottles, and such like articles are either simply blown into the form
required, or into moulds made to close upon the ball of soft glass,
and again open when the required form has been given (fig. 8).
Many articles of glass are cast, or “struck-up” by compression in a
mould, and are often made to resemble cut-glass articles, but they
are much inferior in appearance. The best articles of glass are first
blown, and afterwards cut and polished (see “Glass-cutting”). Of
whatever kind the article of glass may be, it is so brittle that the
slightest blow would break it, a bad quality which is got rid of by
a process called “annealing.” This consists in placing it while quite
hot on the floor of an oven, which is allowed to cool very gradually
indeed. This slow cooling takes off the brittleness; and articles of
glass well annealed, will scarcely break with boiling water, and are
very much tougher than others.