There are plenty of receipts for the composition of flint or crystal
glass, but no mixture that we know can secure a uniform shade in each
pot. The component parts of glass are well known, and the mixer's sure
guide is to watch the effect of heat on each pot, for he soon finds the
mixture that gives good color in one pot will in another in the same
furnace prove bad. If he possesses sufficient knowledge of the chemical
causes, he can correct the evil.
Among the valuable receipts for rich colors is the following, for
RUBY GLASS, which takes lead both in cost and richness:--
Take one ounce of pure gold; dissolve in a glass vessel two ounces pure
sal ammoniac acid, and five ounces of pure nitric acid, which will take
six to seven days; drop in at a time say one twentieth part of the
gold. When the first piece is dissolved, drop in another twentieth
portion of the gold, and so on until the ounce of gold is all
dissolved. This will require twenty-four hours. Evaporate the solution
to dryness. Then prepare in a glass vessel six ounces pure nitric acid,
two ounces muriatic acid, and one ounce of highest proof alcohol; mix
them well together, and drop in pure grained tin a bit at a time,
_but beware of the fumes_. Stir it well with a glass rod; dilute
the solution with eighty times its bulk of distilled water; then take
the prepared gold, dissolved in a quart of distilled water, and pour it
steadily into the solution of tin as above prepared, stirring all the
while. Let it settle twenty-four to thirty hours; pour off the water,
leave the settlings, pour in two thirds of a quart of water. Stir it
thoroughly; let it settle thirty hours; pour off as before, and filter
the precipitate through filtering paper. The result is the purple of
Crassus. The ounce of gold thus prepared must be well incorporated with
the following batch: say thirty-two pounds fine silex, thirty-six
pounds oxide of lead, sixteen pounds refined nitre; melt the same in a
clean pot, one little used, and smooth inside; when filled in, put the
stopper to the pot loose, leaving it slightly open; leave it five or
six hours, or time to settle, then a back stopper can be put up. In the
usual time it will be ready to be worked out in solid, egg-shaped
balls, and exposed to the air to be partially cooled; they are then to
be placed in the leer under a strong fire, which will in two or three
hours turn them to a red color; then the pans may be drawn slowly to
anneal the balls.
It is well known to mixers that colored glass is derived from metallic
oxides. To obtain the proper color depends on the purity and strength
of the metallic oxides. The following receipts have with success been
used:--