Artificial gems are all but varieties of glass. What is called
“paste,” “French diamonds,” &c., are glasses of peculiar brilliancy,
well cut and polished. Garnets, emeralds, and other precious stones
are imitated by coloring the “paste” with various substances, chiefly
metallic oxides, as oxide of cobalt, which produces a blue color,
oxide of copper a red, and oxide of chromium a green color, &c.
Glass is used for a variety of purposes besides the one great purpose
of admitting light to houses while air and damp are excluded. It
furnishes an immense variety of beautiful and useful articles in
the form of drinking-vessels, vases, chandeliers, &c., and to the
chemist and manufacturer generally, it is invaluable, for vessels of
glass thoroughly resist the action of all acids (with the exception
of the hydrofluoric) and nearly every other substance. It stands
a considerable heat, and if made equal in substance and rather
thin, will not easily crack by sudden alterations of temperature.
Without glass, microscopes, telescopes, cameras, barometers and
thermometers--upon which some of our best and most useful knowledge
and some very beautiful results of chemical action depend--could
hardly have been constructed.