ium produces a canary yellow in soda and potash-lime
glasses, which fluoresce, and these glasses may be used in the
detection of ultra-violet rays. The color is topaz in lead glass. Both
sulphur and carbon are used in the manufacture of pale yellow glasses.
Antimony has a weak effect, but in the presence of much lead it is used
for making opaque or translucent yellow glasses. Chromium produces a
green color, which is reddish in lead glass, and yellowish in soda, and
potash-lime glasses.

Iron imparts a green or bluish green color to glass. It is usually
present as an impurity in the ingredients of glass and its color is
neutralized by adding some manganese, which produces a purple color
complementary to the bluish green. This accounts for the manganese
purple which develops from colorless glass exposed to ultra-violet rays.
Iron is used in "bottle green" glass. Its color is greenish blue in
potash-lime glass, bluish green in soda-lime glass, and yellowish green
in lead glass.

Cobalt is widely used in the production of blue glasses. It produces a
violet-blue in potash-lime and soda-lime glasses and a blue in lead
glasses. It appears blue, but it transmits deep red rays. For this
reason when used in conjunction with a deep red glass, a filter for only
the deepest red rays is obtained. Nickel produces an amethyst color in
potash-lime glass, a reddish brown in soda-lime glass, and a purple in
lead glass. Manganese is used largely as a "decolorizing" agent in
counteracting the blue-green of iron. It produces an amethyst color in
potash-lime glass and reddish violet in soda-lime and lead glasses.

These are the principal coloring ingredients used in the manufacture of
colored glass. The staining of glass is done under lower temperatures,
so that a greater variety of chemical compounds may be used. The
resulting colors of metals and metallic oxides dissolved in glass depend
not only upon the nature of the metal used, but also partly upon the
stage of oxidation, the composition of the glass and even upon the
temperature of the fusion.

In developing a glass filter the effects of the various coloring
elements are determined spectrally and the various elements are varied
in proper proportions until the glass of desired spectral transmission
is obtained. It is seen that the coloring elements are limited and the
combination of these is further limited by chemical considerations. In
combining various colored glasses or various