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82 PRECIOUS STONES
Some
Cape and Bahia diamonds do not show as good color play by artificial
light as by daylight, though generally it is the reverse.
Usually,
artificial light destroys the yellow color in a stone, and electric
light intensifies it. Canaries lose their distinctive color by
artificial light; they should be shown in a strong natural light, as
they do not appear to advantage in a dull or even in a waning light.
Blue
in a stone is sometimes intensified by sunlight. In other cases the arc
electric light will give to some diamonds a deep violet hue.
Cape stones run to yellow, but the tendency of the Brazilian is towards green.
Although
in ancient times some diamonds, as well as emeralds and other gems, may
have been found in Africa, the oldest known diamond-fields which have
been continuously worked are the Indian. In common with all other
diamond-mines except those of South Africa, the Indian diamonds are
found scattered among the sands and gravels, long since released by the
processes of time from their matrix, carried by waters and deposited in
the beds arid along the course of streams and rivers in the superficial
strata of the earth in the valleys. They are found, as a rule, at a
depth varying from two or three feet to fifteen or twenty feet,
occasionally fifty feet. In the South they occur on the banks of the
Panar and between that river and the Kistnah. At the western end of
this diamond-bearing territory is the celebrated Wajrah Karrur
district. To the east, towards the mouth of the Kistnah, and on its
southern banks, are the Kollur mines, called by Tavernier " Gani
Coulour," sometimes spoken of as " Gani" only. Still farther east, and
on the northern side of the Kistnah, are the Partial mines. This
district lies almost due east of Golconda, a name often used to
distinguish the diamonds of this region, and sometimes as a
designation of all Indian diamonds.
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