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management, the maximum of breakage may be calculated at 10 per cent.
Next to the duration of pots, the success of the manufacturer depends
upon constant attention, and skilful management of the lears.*
COLOURED GLASS.
Dark, massive, coloured Glasses, formerly
made in Flint Glass-houses—whether blue, green, amethyst, or
other colours, for hyacinth, hock, and finger glasses, or in large
cylinders for cutting and flattening into Window Glass—have been
almost superseded; the latter by Crown Glass-makers, and the former by
lighter or less dense Flint Glass colours.
The introduction of toilet and
smelling-bottles has created a demand for light-tinted Glasses,
particularly for the beautiful semi-opalescent, yellowish-green colour;
produced chiefly by the expensive oxide of uranium, mixed with a slight
portion of copper, and appearing yellow or light green, just as the rays
of light happen to fall upon the unequal substance or thickness of the
Glass. This chameleon-like effect is also produced by uranium alone,
used as the colouring oxide for gold topaz; it has been much in demand
for hock glasses and decanters, and many ornamental articles of glass;
but its fascinating peculiarity is lost, indeed, its colorization mostly
fades, by candle-light.
The superior purity and refractibility
of our Flint Glass is particularly adapted to display the delicacy and
beauty of
* Unannealed Glass exhibits the
effects of polarization of light; which being a philosophical subject,
is not considered sufficiently practical to come within the plan of
this work.
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