pose
of ascertaining these facts, a crystal of sapphire (which may be
obtained easily and without expense), a piece of quartz or rock
crystal, a piece of hard flint-glass, and a pair of scales for the
purpose of taking the specific gravity, are all that is necessary.
Those persons who are in possession of an electrometer or a polarizing
apparatus, have valuable adjuncts to the simple tests here indicated.
A
very common mode of fraud, practised on inexperienced persons in cut
stones, is the "doublet," or "semi-stone." In this case the top of the
stone is genuine and the under-part glass, joined together
artistically with cement; sometimes, for instance, the top is
sapphire, and the under-part a gem of less value, such as garnet. "When
set, these stones are very difficult to detect, and frequently deceive
the most experienced. When the under-part is of glass, however, the
application of the file to the under as well as upper surface will, of
course, at once show the imposition. Set stones which are set with a
back are generally of pale colour or small lustre, often set with
coloured foil, to enhance their beauty. Sometimes, however, stones
which are set open, or, to use the technical term, ' azur,' have the
interior of the setting enamelled or painted, to throw a tint of
colour into the gem; or, in the case of the diamond, have the inside
of the setting of polished silver, to correct a yellowish tinge. In all
these cases, to be forewarne'd is to be forearmed, and a careful
examination will prevent any one being deceived by these means.
