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Ch. 10: Mounting Stones

Ch. 9: Synthetic Gems Page of 187 Ch. 11: The Diamond Text size:minus plus Restore normal size   Mail page  Print this page
consists of glass and the lower portion some mineral or glass separated by a piece of foil, a coloured layer or a thin plate of coloured mineral to give the stone a desirable tint. By immersing in liquids with proper refractive index, the deception could be easily detected.
Chapter X
PRECIOUS METALS FOR MOUNTING GEM-STONES
GOLD, platinum and silver are widely used for mounting gems, but gold and platinum are the more important as they do not tarnish as silver. As pure gold is very soft and malleable, for a durable mounting, it is usually alloyed with. other metals to increase its hardness. The gold content of the alloy is expressed in carats or l/24th parts. Usually, 18 carat gold containing 18 parts gold and 6 parts alloy has good wearing qualities. The usual alloys are:— yellow gold: 18 parts gold, 3 parts silver, and 3 parts copper by weight (darker shades are obtained by increasing copper content); white gold: 75% gold, 17% nickel, 2.5% copper, and 5.5% zinc (this alloy is harder and more durable than platinum and iridium and serves as a substitute); green gold: 75% gold, 22.5% silver, 1.5% nickel and 1% copper (it is also used for mounting purposes).
Pure platinum is soft and flexible and has to be alloyed with a metal to give necessary hardness and rigidity. Alloyed with 10% iridium, hardness of platinum is considerably increased. This is also suitable for mounting gems. Silver is not used for mounting of gems.
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Ch. 9: Synthetic Gems Page of 187 Ch. 11: The Diamond
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