Cleansing of jewelry
Of course, porous stones such as opal and turquoise should not be subjected to this treatment. The cleansing of jewelry and stones is really best left in the hands of the jeweler, who has the necessary solutions and facilities at hand.
Many large stones are recognizable by dealers in the trade if they have passed through their hands. But there is an institute in Paris which not only pursues scientific research in gem stones but also issues certificates to owners of tested stones, showing the individual properties of their specimens. A micro-photograph is also kept, which would identify the stone in case of theft, besides eliminating possible fraud whenever it is resold.
Let us now summarize the factors which determine the value of a diamond, in their order of importance:
1. Weight (size).
2. Color. Pure white is the best.
3. Flaws. Cracks are more detrimental than spots.
4. Form of cutting. Modern brilliant cut is the best.
We shall now pass to other jewel stones of commercial importance. With sapphires, the most popular color is blue, and the finest are the deep transparent blues which are neither dark nor pale. Stones should be homogeneous in color and bright. Differences in shade within the one stone detract from the value, and one ought to view a sapphire in the artificial light as well as in daylight. Many specimens change to an amethyst blue by artificial light, and these are not worth so much as the Cashmere blue stones, which retain their color under these different conditions.