Colored
glass is also very frequently cut in forms and shapes so as to resemble
gems, and the various colors are produced by melting the best qualities
of glass materials with the following oxides :
Yellow is produced by charcoal, antimonite of potassa, ' silver, and oxide of uranium.
Blue, by oxide of cobalt, and a mixture of copper and iron.
Green, by oxide of copper or of chrome, or by antimonite of potassa, litharge, and cobalt.
Red, by gold, suboxide of copper, and oxide of iron.
Violet, by manganese.
Black, by protoxide of uranium, iridium, platinum, and by a mixture of manganese, copper, iron, and cobalt.
White, by oxide of tin, arsenic, and bone"-ashes.
By
combining one or more of these oxides various shades and hues may be
obtained ; the yellow glass of antimony may be shaded more into orange
by the use of a little oxide of iron ; the purple-red of gold passes
into carmine by employing silver with gold ; the blue of cobalt may be
shaded into purple by a little gold ; into green by antimony,
