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Ch. 5: Imitation Gems & Artificial Production

Ch. 5: Imitation Gems & Artificial Production Page of 311 Ch. 5: Imitation Gems & Artificial Production Text size:minus plus Restore normal size   Mail page  Print this page
PRECIOUS STONES.                                 73
For imitation topaz the above formula is used minus the gold, and the fusion is not carried out at such a high tem­perature. In using gold for colouring purposes, the greatest care has to be taken to avoid clouding due to reduction of the gold to the metallic state. The colour taken on at first is yellowish-green, or maybe, brown, a deep ruby-red being obtained on annealing.
Although not much used for colouring imitation precious stones, there are many other methods. Various shades of yellow may he obtained by the addition of finely-powdered coal to glass free from lead, and uranium glass is coloured by the use of uranium salts.
Paste has to be cut and polished in the same manner as real stones, only, owing to the inferior hardness, the process is much more simple. Nearly all pastes are cut as brilliants,
Ch. 5: Imitation Gems & Artificial Production Page of 311 Ch. 5: Imitation Gems & Artificial Production
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