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| The Treatment of Gemstones
||Gem Dealers's Secrets - Handbook for the Gem Buyer
Copyright © Sondra Francis, G.G. 1999
Table of Content
The treatment and enhancement of gemstones has existed for centuries. Some enhancements improve on nature slightly, are undetectable, and they are permanent; this provides the gem market with a larger supply of beautiful gemstones. Other treatments produce dramatic changes in the gemstone; the irradiation and heating of colorless topaz that permanently transforms it into blue topaz is an excellent example. A few treatments are less stable and should be avoided by the knowledgeable buyer.
Generally treatment of a gemstone is done by the cutter or lapidary. Since he makes the investment of buying the gems rough he wants the final product to be as salable as possible. Sometimes gemstones are treated as rough stones. The heating of sapphires and rubies is done before the rough stones are sold to the cutters. Most of this treating is done in countries that cut and mine the stones. By the time the stones enter into the United States market it may have passed through several hands and disclosure of treatment may not always occur.
Ideally disclosure of enhancement is the job of the seller, but it does not always happen. Realistically an informed buyer protects himself. How does treatment affect the price of gemstones? Each gemstone variety must be considered individually as well as each type of treatment. Some gemstones would not be commercially available if they were not enhanced. Citrine and tanzanite are extremely rare in nature; these varieties are dependent on heating to produce enough supply to meet the demands of the market.
There are some gemstones that are not enhanced by present technology; these include: garnets, peridot, iolite, spinel, all varieties of chrysoberyl, catseye tourmaline , malachite, hematite, and all feldspar including all varieties of moonstones. Keep in mind that new technology in gemstone treatment is always changing and new treatments are appearing.
Heating is not generally detectable by today's method and it is irreversible under normal conditions. In general, there is no price difference between heated and unheated gemstones because it is not detectable. In most cases the heating enhances the gemstone to make it more beautiful, so a higher price may result. Tanzanite, citrine, pink topaz, blue and colorless zircon would not be available without heating, so the enhanced product will command a higher price than the rough material from which it originated. However, unheated rubies and sapphires may contain microscopic rutile needles or tiny gas bubbles in pockets of liquid which are evidence that laboratories can use to guarantee that these stones have not been heated. If these gems are the finest color they will command premium prices due to their extreme rarity.
But remember, if an emerald is put into an ultrasonic or is steamed clean, then the oil may be leached out and fractures could reappear whiter and more obvious. In this case, the stone can be re-oiled.
Rarely you may see a ruby which is oiled; but only if it is of very low quality. Very rarely colored oils are used on emeralds and rubies. The idea is to add color while concealing fractures. You want to avoid buying these because you can't judge the true color. This is done to deceive the buyer. Fortunately this is not common and it is unlikely you will encounter this if you buy from a reputable source in the United States. Synthetic resins can be used to fill in fractures in emeralds and other stones with fractures that reach the surface of the gem. Hardeners are often applied to make the process permanent.
Tourmaline can be irradiated to darken pink stones into red ones; these are indistinguishable from natural red ones. In this case the tourmalines would sell for the same price if color were comparable.
Off colored diamonds can be irradiated and heated and turned into intense greens, yellows, blues and browns. These are not commonplace, but if you are buying a fancy colored diamond particularly a green one, it is a valid question to ask the seller. Irradiated diamonds will sell for much less per carat than the naturally colored ones of comparable color, clarity grade, and size. Cultured pearls can be irradiated to produce gray or blue colors; but dyeing in these colors is more common. Irradiated pearls will sell for about the same price as the dyed pearls, this should be well below the prices asked for pearls with very fine colors.
Japanese cultured pearls, which are grown in an Akoya oyster that produces pearls up to about l0 millimeters, grow into a limited selection of colors with various overtones of colors. If they are dark gray, bluish, violet, nearly black, or intense bronze, assume they are dyed. To meet current demand for pearls with rose overtones, some cultured pearls have been given a pink tint; this can be detected by looking for concentrations of dye around drill holes or around blemishes. On the other hand, South Sea cultured pearls which are generally larger than the Japanese cultured pearls, may grow into a variety of exotic colors naturally because they are grown in a different variety of oyster. Tahitian black pearls are a good example of naturally colored black pearls. Cultured pearls with a natural exotic color will command a much higher price than a dyed one.
Dyeing of chalcedony and of pearls is prevalent, permanent, and acceptable. These colors do not occur in nature; no deception is involved. But dyeing of other materials, jade, lapis lazuli, turquoise, and coral, may be less acceptable. Generally, dyeing of these materials is done to disguise poor quality goods. Dyed lapis lazuli can be easily tested by rubbing it with a piece of cotton soaked with acetone (fingernail polish remover). If it is dyed, blue color will eventually rub off on the cotton. Dyed lapis should be much less expensive than fine natural lapis. In the case of lapis lazuli or turquoise, the natural material is not that expensive, so why bother with inferior material unless it is irresistibly cheap? Dyed lapis lazuli may bleed blue onto the wearer or his or her clothing.
Dyed jade may be tricky to detect, so be careful if the price seems "too good". Coral beads may also be dyed. But if you are buying your mother-in-law a gift from Waikiki you may justify a purchase of dyed coral beads if they are very inexpensive.
Impregnation and stabilization
Recently a new process to fill fractures in diamonds has been introduced. These are referred to as "Yehuda filled diamonds" after the creator of the process. The filling masks large inclusions that would be visible to the eye. Cracks must reach the surface to be filled; if the diamond is subject to high heat as it would during retipping the filling could melt out. This is considered an acceptable practice in the diamond trade but only if the seller tells you about it. Keep in mind that the original diamond before treatment would have had a very low clarity grade, so the treated stone should be priced accordingly. One difficulty is that you are unable to see what the stone really looks like so it is difficult to know what the price should be.
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