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Sec. II, Ch. 1: The Diamond

Sec. II, Ch. 1: The Diamond Page of 366 Sec. II, Ch. 1: The Diamond Text size:minus plus Restore normal size   Mail page  Print this page
6o                                  The Diamond.
In many Diamonds the core is not pure, but shows blackish or greenish spots. This is more particularly the case in the green stones. Many Diamonds have also " feathers " and fissures, which materially modify the passage of light, and of course diminish the value of the stones.
Black Diamonds of great beauty are occasionally supplied by Borneo, which are so adamantine that ordinary Diamond-dust makes not the smallest impression upon them ; and they can only be ground or polished by using their own dust for the purpose. Of late black Diamonds have been much sought after.
Phosphorescence, &c.
Phosphorescence is produced not only by heat, but also by the action of light, and persists long after removal from the luminous source. The Diamond becomes phos­phorescent under the influence of the sun's rays, or by insolation, and remains glowing for some time after removal from the sunshine, even when covered with cloth, leather or paper. It appears that this property was first recorded by Boyle in the year 1663.
The phosphorescence is most striking after the Diamond has been exposed to the blue or more refrangible rays of the spectrum ; under the red rays, or rays of low re-frangibility it is much weaker. The author on one occasion exposed a fine orange-coloured Diamond of about 115 carats to the prolonged action of a powerful lime-light, and then removed it to a dark-room, when the phos­phorescence was sufficient to light up the apartment. All Diamonds do not ph®sphoresce after exposure to light, but Diamonds of yellow colour seem peculiarly susceptible to luminous influences.
Sec. II, Ch. 1: The Diamond Page of 366 Sec. II, Ch. 1: The Diamond
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