84 PRECIOUS STONES
rubies
there are found slight hollows corresponding or analogous to the
bubbles found in melted glass, it becomes a matter of great difficulty
to distinguish the real from the imitation by such tests as hardness,
specific gravity, dichroism, and the like, so that in such a case,
short of risking the ruin of the stone, ordinary persons are unable to
apply any convincing tests. Therefore, only the expert can decide, by
his appreciation of the delicate shade of difference in the light of a
true ruby and that of an excellent imitation, and by the distribution
of the colour, which—however experienced the chemist may be, or with
what care the colouring matter may have been incorporated in the
mass—has been found impossible of distribution throughout the body of
an artificial stone so perfectly and in the same manner and direction
as nature herself distributes it in the genuine. This alone, even in
the closest imitations, is clear to the eye of the expert, though not
to the untrained eye, unless the stone is palpably spurious. To one who
is accustomed to the examination of precious stones, however perfect
the imitation, it is but necessary to place it beside or amongst one or
more real ones for the false to be almost instantly identified, and
that with certainty.
The Sapphire.
The
Sapphire is not so easy to imitate, as its hardness exceeds that of the
ruby, and imitations containing its known constituents, or of glass,
are invariably softer than the natural stone. As before remarked,
almost any form of corundum other than red is, broadly, called sap-
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