tinuance;
for real gems retain, after being rubbed, their electricity for from
six to thirty -- two hours, whereas, the artificial ones only retain it
from forty to sixty minutes.
S. The Doublets. This
mode of imitating real gems is called doubling, when a quartz, cut and
polished, is cemented by means of gum mastic to another colored paste,
whereby the whole stone assumes the color of the lower paste. When a
real gem is employed instead of quartz (as the surface and the quartz
or paste is cemented below), it is called half doubling. This
adulteration is carried on to a very great extent in the East Indies,
where they paste any thin gem to a paste corresponding in color.
The concave doubling is
effected by excavating the inside of a quartz or paste. The cavity
being filled with a colored fluid, and the other part afterwards
cemented on it, will, when well executed, present so uniform a color
that it is difficult even for a judge to detect the deception. The
surest method of detection is to put the specimen in question in hot
water or alcohol, by which the gum mastic will be dissolved. When set,
the only way of finding out the adulteration., is to put it reversely
on the nail of the thumb, when the false refraction of light or the
rainbow colors will, with certainty, determine its identity.
C. The Burning. This
mode of adulterating the real gems, is performed by coloring cut and
polished quartz specimens.and throwing them into a solution of
permanent pigments, such as a solution of indigo, decoction of
cochineal, solution of ammoniacal copper; the small cavities produced
by the heat will absorb the fluids. The topaz is burnt by itself, with
or without the absorption of a pigment, as also the spinelle, and the
quartz; chalcedony is, however, frequently burnt to imitate the onyx,
and to engrave thereon cameos and intaglios.
It 'may be remarked, however, that since the introduc-
