HEIGHTENING THE COLOR OF GEMS. 169
to Hawkins, the following method is pursued in England: The emery is
pulverized in an iron mortar and passed through different sieves, one
finer than the other; the first is levigated with oil, which keeps it
in better suspension in water; according to the time in which the
powder settles, the different numbers are obtained.
polishing the different precious stones, hard and soft gems, the
diamond powder and emery are mostly used. Rotten-stone, tin-ashes,
jsumice-stone, oxide of iron, English jewellers'-red, are all used in
their finest pulverized state. A great deal depends upon the polish
which a gem has received ; all its other superior qualities being
thereby called forth.
HEIGHTENING THE COLOR OF GEMS.
color is one of those characters which is the most tempting in the sale
of gems and jewelry, all means are ployed for heightening the same, and
covering any real defect. Foil of small thin metallic substances,
colored or uncolored, either of fine silver or copper, is placed under
the gem in the back of the mounting, which heightens the color and
lustre, particularly of the transparent gems. Almost all gems were
formerly set in black-colored backs, composed of burnt ivory-black and
gum mastic, but are now mostly set d jour, which is, leaving
the lower part of the stone uncovered in setting, and only mounting
around the girdle—an old method, and very applicable to perfect stones,
where no defects require concealment.
materially heightens the lustre of gems. The rose-diamond always
requires it on account of its flat form. There are many gems which
would not produce any effect without the foil; it is therefore used
whenever a pale or impure color is to be raised, or when the "gems are
to be protected against dust or moisture in order to produce a