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The organic products used in jewelry are quickly affected by heat.’Pearls are completely spoiled; they turn brown and split. Amber burns with a camphor-like smell, giving off black fumes. Coral loses its color and decrepitates.
One other result of heating may be mentioned here, and that is the property which a few gem stones possess of emitting light, known as phosphorescence. This must not be confused with fluorescence. Pieces of quartz, when rubbed together in a dark room, give off a phosphorescent light, while heated fluorspar displays a very bright effect. Exposure to strong sunlight is sufficient to produce this effect in some minerals. Diamonds, especially yellow tinted specimens, are highly phosphorescent; apatite, a mineral occasionally cut as a gem stone, is slightly phosphorescent. Such effects may be more easily observed if the specimens are transferred quickly from the sunlight to a dark room.

The application of heat to improve or alter the color of stones needs considerable care, patience, and experience. Many stones are spoiled in such attempts to improve on nature and increase their commercial value. Zircon and the different varieties of quartz are perhaps the chief victims of man’s enterprise in this direction, and it is only the cost and the rarity of raw material thai limits greater experiment. But the artificial perfecting of precious stones may yet be one of the achievements of the future chemist or physicist.