160 A POPULAR TREATISE ON GEMS.
justed,
a little oil and diamond powder is dropped on the plate, it is set in
motion at the rate of about two hundred revolutions in a minute, and
the process of grinding down, and at the same time of polishing, is
begun. The diamond is taken up and examined from time to time, and is
adjusted so as to give-the facet its true form. The heat occasioned by
the friction is at all times pretty considerable, and when the pincers
are heavily laden, it occasionally increases to such a degree as to
soften the solder and displace the diamond. This is a serious
accident, frequently occasioning a flaw in the diamond, and always
tearing up the surface of the skive, so as to damage it very
considerably. There is room on the skive for three or four diamonds at
the same time; and to give each its proper share of attention, is as
much as one person can well manage. The completion of a single facet
often occupies some hours."
The
polish is often produced by rubbing the diamond with a cloth or bare
hand. The form which the gems have to receive from the lapidary varies
according to the condition of the stones; and the skill of the artist
consists in the right selection of a form which shall correspond with
the natural structure of the gems. A good cut has the greatest
influence on the lustre and beauty of gems; the colorless and limpid
gems, for instance, require a different form from those which have a
play of colors. With a diamond, the form must correspond as much as
possible with its natural or original shape, in order to save the great
trouble of grinding, and the waste thereby produced. Transparent gems
ought not to be cut too thick; the rays of light might otherwise be
refracted too much, or prevented from penetrating through them at all:
in the first instance, the lower facets do not act in correspondence
with the upper, and the rays are much distributed before reaching the
eye. Gems of such description are called clotty. On the other
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