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Pearl Treatments
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impossible for gem labs to prove that yellow pearls are of natural color. Off-color pearls from the Akoya and silver- or gold-lip oysters are sometimes darkened with dye to improve their appearance. Then they are sold as "black pearls." Some of the dark dyes make the pearls look iridescent. If black pearls are smaller than 8 mm, just assume they are dyed Akoya pearls. Dyeing these small pearls is an accepted trade practice because it
provides con­sumers with an option that is not available from natural-color Akoya pearls. Nevertheless, the treatment must be disclosed.

Light-colored pearls from the black-lip oyster are occasionally darkened when there is low demand for very light Tahitian colors. Many people associate the term "dyed" with the terms "cheap" and "fake. " However, dyed black pearls were sold in fashionable stores as far back as the 1930's-long before black pearls were being commercially cultivated. Dyed black pearls were considered elegant. They are still in demand. Plus, they have the added bonus of being much more affordable than their naturally-colored counterparts. A large percentage of the pink pearls sold in stores have also been dyed and this means there's a wider selection of pink pearls available for consumers.

If pearls are not properly dyed, the color won't be stable. Therefore it's important to buy dyed pearls from reputable jewelers. That way if there is a problem, you'll be able to return the pearls and get a refund. If you're buying expensive untreated pearls, have them checked by an independent gem laboratory.

In recent years, there has been a problem of nacre peeling off of dyed Akoya pearls with thin nacre. On dark pearls, chipped nacre can be quite noticeable and unattractive. As a result, some dealers have stopped selling dyed Akoyas to avoid the hassle of returns and customer complaints.

Irradiation: This method works best on freshwater pearls, but off-color Akoya and South Sea pearls may also be darkened in this manner. It involves bombarding pearls with gamma rays. This blackens the shell bead nucleus of Akoya and South Sea pearls and can make their nacre appear dark if it is ' thin. Sometimes pearls are both dyed and irradiated. The irradiation will give them an iridescent bluish or greenish gray color and the dye will further darken their appearance.

Silver salt treatment: This is the most common way of blackening Akoya pearls. The pearls are soaked in a weak solution of silver nitrate and diluted ammonia and then exposed to light or hydrogen sulfide gas. Unfortunately, the silver nitrate tends to weaken pearls and make them more susceptible to wear. Silver nitrate treatments can usually be detected by X-radiography.

Dying the bead nucleus: Occasionally shell bead nuclei are dyed before they are inserted in the oyster. Afterwards the dark bead may show through the nacre and make the pearl nacre look dark.

Natural Color or Not?

As you can see, dyeing is not the only means of coloring pearls. However, for the sake of brevity, the term "dyed" will be used in the rest of this chapter to describe any artificially colored pearl. Dyed pearls are not fakes, but they are normally considered less valuable than those of natural color. There is an especially large price difference between true black or golden South Sea pearls and those which aren't, so you should know how to protect yourself from being charged a natural­color pearl price for a dyed pearl. Even if the price is fair, you may just prefer pearls of natural color. You can reduce your chances of being misled with the following tests:

Price Test:   Is the price unusually low compared to natural-color pearls of the same size,
- sale7 - cheaps2