Pearl treatments are defined as any action other than polishing which alters a pearl's appearance which may include; irradiation, bleaching, heating, filling, waxing, drilling, cutting and working.
Pearl Treatments After Harvesting
After harvest, pearls are always processed in one way or another. Akoya and freshwater pearls are routinely bleached, and all pearls are cleaned and polished before sale. However, there are treatments that should be noted with cultured pearls that change the aesthetic qualities of the gem.
Different Kinds Of Pearl Treatments
When a low-quality cultured pearl is cleaned and polished, and still does not have a good luster, the farmer is left with a few options. He can sell the pearl at a steep discount; dispose of the pearl; peel the nacre to sell it, then reuse the nucleus; or apply a treatment to the pearl that will change its appearance. If the pearl is a good candidate for treatment, this is the most common and economically sensible approach for the farmer.
There are three main treatments that low-quality pearls undergo:
- Dyeing: The use of silver nitrate or other organic dyes to darken the nacre of the pearl.
- Irradiation: The use of gamma rays to darken the nucleus of the pearl in akoya pearls and the nacre layers in freshwater.
- Luster treatments: A pearl is heated and then cooled or a coating treatment placed on the surface of the pearl to artificially enhance the lustre. This is also referred to as "maeshori".
Using Silver Nitrate In Pearl Treatments
Silver nitrate has been used for many decades to darken the appearance of pearls. The chemical penetrates the layers of nacre and has a chemical reaction with light and hydrogen sulfide gas to create a rich black color. If the farmer wishes to create colors other than black, he may also use organic or inorganic dyes to produce another color variation. This is a very popular treatment done to freshwater pearls, as the lower values give farmers more opportunity to experiment. Akoya pearls are also routinely "pinked" to enhance a more desirable rose overtone.
Using Irradiation In Pearl Treatments
Irradiation has differing effects on freshwater and saltwater cultured pearls. The gamma rays do not affect the nacre layers of saltwater cultured pearls, but in fact darken the nucleus of the pearl. An irradiated saltwater pearl appears to be gray or blue. The nacre of freshwater pearls, on the other hand, when affected by gamma rays can become very dark. Some of these freshwater treated pearls will also have an intense metallic sheen and iridescent orient over their surface.
Using Coating In Pearl Treatments
Coating a pearl to enhance its luster is not widely practiced and is greatly frowned upon. This coating is equivalent to a coat of clear nail polish. Although the luster may appear to be fine, the coating may eventually chip or peel, leaving a low-luster pearl visible beneath the surface. This is a treatment to watch for, as dishonest pearl dealers have passed these pearls on to unsuspecting consumers in the past.
How To Detect Pearl Treatments
Although nearly all pearls on the market today have been treated in some way, it can be difficult to detect pearls treated to change color. One method of detecting dyed or irradiated pearls is to check the matching of the strand. A strand of natural color pearls will typically vary slightly from pearl to pearl. A perfectly consistent strand may be evidence of treatment. By peering down the drill hole of a dyed pearl, one may also be able to see concentrations of color. This residue is left from the dying process. When looking down the drill hole of an irradiated pearl, one may be able to detect a darkened nucleus. This is strong evidence of gamma-ray treatment.
How To Detect Luster Pearl Treatments
Luster treatments are much harder to spot. The most basic method, however, is to compare an untreated strand with the suspect strand under at least 50X magnification. The untreated pearl will have a scaly nacre surface. The coated pearl will have a smooth, glass-like surface.
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