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74 PRECIOUS STONES.
this
method setting the stone off to best advantage. It needs a fairly big
stone to work upon, as the brilliant is almost as thick as it is broad.
Real Diamonds that are not large enough or contain too many flaws to
permit cutting in this way are "rose" or "table" cut; but such a method
adopted for paste would be useless. Paste absorbs a considerable
amount of light, especially through the " table." But this is not so
with the Diamond; almost the whole of the light falling upon it is
entirely reflected off again, that which is absorbed being thrown out
by the lower facets. It is to this property of strong refractivity and
reflection that the Diamond owes its brilliant play of colours, and
experts can tell real stones at a glance, by their "fire." If an
imitation diamond cut in any form be placed in a good light and turned
about in various directions the table will" in certain positions appear
as a black spot surrounded by a white circle of light. The white circle
of light is due to reflection from the small facets between the table
and girdle, and the blackness of the table itself is largely due to a
great portion of the light falling upon it being absorbed and not
thrown out again by the lower facets.
Imitations
when examined with a lens are frequently found to be highly fractured
round the girdle where clasped by the setting; the fractures being
conchoidal or shell-like and characteristic of glass. Eeal stones
rarely show this, at least not round the girdle, but Diamonds are
extremely liable to flaws, and I strongly recommend that purchasers of
stones smaller than 1/8 of an inch in diameter, or less than one carat
in weight, should examine them carefully with a powerful lens. One
stone purchased by me some time ago
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