Pearl Treatments Explained

Nothing is more natural than a pearl. Unlike gemstones, regularly cut and polished to unleash their beauty, pearls arrive ready-made, as natural as when they emerged from the creature that conceived them — or do they?

Since the beginning of time, man has sought to improve upon nature. Pearls are no exception. The majority of today's cultured pearls have undergone some form of processing or treatment after their removal from the mollusk. The only way to confidently buy in the wholesale arena is to learn what to look for and what to beware of.

Pearl treatments are driven largely by price and demand. As producers are pressured to produce greater quantities of lower-priced pearls, cultivation times decrease. Pearls that once were allowed to remain within the mollusk for several years are now removed after just eight months. This results in thinner-nacred pearls that do not exhibit the sumptuous luster and orient of their thick-nacred predecessors. Thin nacre can result in pearls that chip, crack, or rapidly lose their beauty. This then stimulates the need for more treatments to improve inferior-quality pearls.

Ironically, experts agree that pearls are looking better than ever before. When asked about the pearls on display at this year's Tucson gem and mineral shows, Fred Ward, graduate gemologist and author of Pearls, says, "The quality, polish, and colors today are substantially different and often better." While producers don't exactly compare notes, each will be trying various enhancements to make their pearls more attractive. "With all the things they are trying, much of the output is looking better," he adds.

When first extracted from the oyster or mussel, pearls are tumbled and cleaned to remove residue and odor. That may be all that is done to the finest-quality cultured pearls. Many pearls, however, may be subjected to other processes or treatments to enhance their beauty. "Treatments have become routine in the pearl industry today. This was not the case 20 years ago," says Antoinette Matlins, gemologist and author of The Pearl Book: The Definitive Buying Guide.

Some treatments are relatively benign. Others may compromise pearl quality, leading to pearls that deteriorate with normal wear. Understanding treatments is critical to buying pearls that will last.

After the initial cleaning, bleaching is often used to lighten and even out pearl color. The first layer deposited over the surface of a nucleus is conchiolin, a dark, porous protein. Bleaching lightens this layer. This is especially important when the nacre is too thin to mask the dark layer, so pearls with thick nacre often do not require bleaching.

With the exception of most South Sea cultured pearls and American freshwater cultured pearls, the majority of the white pearls on the market are bleached — although the treatment is rarely disclosed.

Polishing is another common practice. Pearls are often gently tumbled with natural materials — anything from slivers of bamboo to ground-up walnut shells to eucalyptus leaves — in an oily medium such as beeswax that smoothes out small imperfections, generating a greater polish and enhancing luster. "It's simple and non-intrusive," says Ward. However, the beeswax or other oily substances used to improve luster will wear off over time.

Taking such treatments a step further, various substances may be used to fill in cracks, pits, or drill holes in pearls. These often blend in with the color and luster of the nacre, but can sometimes be detected using a loupe. Occasionally epoxy substances are used to fill low-quality baroque pearls if they are hollow or have a loose nucleus. This improves durability and makes them more solid.

Not-So-True Colors

The most commonplace form of color enhancement is dyeing. Pearls are dyed to satisfy the tastes of a particular market, to provide colors that are rare, such as golden South Sea pearls, and to make it easier to create a matched strand. It may take a producer of Tahitian pearls two to three years to accumulate sufficient matching, natural-colored pearls to string a necklace. Dyeing pearls dramatically shortens the wait.

Japanese akoya producers discovered early on that consumers in different countries preferred specific shades of pearls, explains Ward. Americans still like their pearls with a pink tone, Germans like white pearls, the French and South Americans prefer a cream color, and buyers in Arab nations like them creamier still. "All these pearls are coming out of the same oysters in the same water — something must have been done to produce that range of colors," says Ward.

Dyed pearls are typically lower-priced than comparable untreated cultured pearls. Pearls are dyed after drilling, and dye can often be detected by looking at the drill holes and surface imperfections with a loupe for concentrations of color.

Since untreated Tahitian black pearls start at approximately 8 mm in size, it's safe to assume that any black pearls under 8 mm have been dyed. Buyers can also rely on their eyes. "If the color is too perfect or just looks unnatural — it probably is," says Ward.

But there are other ways to enhance color in pearls, and some of them are more difficult to detect. Jack Lynch of Sea Hunt Pearls reports spotting a strand of heat- and pressure-treated chocolate-colored Tahitian pearls at this year's Tucson shows. "As soon as you see something like that, that's brown and well matched in color, you need to ask questions, because it's not something that we normally see," he says.

Heat treatment has also been used to turn white-colored pearls golden. Labs can often detect heat-treated pearls using UV spectroscopy, and experts advise buyers unsure about what's been done to their pearls to send them to a lab for verification.

Irradiation with gamma rays is a last-ditch solution for any pearls that are not salable, says Ward. It darkens the pearl and imparts a blue or green iridescence. Sometimes these are sold as Tahitian black pearls, but the color and shine usually look suspicious.

The good news for people who sell pearls, particularly at the high end, is that all of these treatments are known, and producers don't seem to be developing any new ones.

New treatments are generally driven by a lack of supply, notes Tom Moses of the Gemological Institute of America. "Fortunately, with cultured pearls, South Sea and Tahitians, there has not been a supply issue over the last four to five years, so therefore there is not much new as far as treatments."

However, there is increasing pressure for wholesalers who deal in expensive pearls to prove that they haven't been enhanced. "Diamonds travel with paper today," says Ward. That segment of the gem industry demands lab reports for color and clarity. It hasn't happened in the lower end of the market because the pearls aren't that expensive, but the high end is moving in that direction.

The debate in the industry centers around what exactly is considered a treatment and how it should be disclosed. Federal Trade Commission guidelines require full disclosure of pearl treatments to consumers. With a few exceptions, they are ignored.

"The customers don't know enough about it to be concerned," says Ward. "It may not even be significant [in making the sale]." He attributes the lack of disclosure to the many middlemen between the producers and the final retail sellers; sometimes wholesalers simply don't know what's been done to the pearls, especially those dealing in inexpensive goods.

But at the heart of the matter is the judgment issue of whether treatments are acceptable to the end customer or not. For industry experts, they are an inevitable part of the industry and are acceptable if disclosed. "I think this is legitimate, and, for me, it is not a problem," says Peter Fischer, director of the pearl division for the Golay Group. The key is to present this information in a way that everyone understands, he adds.

Lynch advocates a proactive approach. "I think it's the industry's obligation to drive disclosure regarding pearl treatment. If we handle it from our end, we're educating the consumer, educating the retailer, and putting ourselves forward as honest dealers of pearls," he says.

Experts advise novice buyers to look at as many pearls as possible and ask questions to develop a feel for what is natural and what is treated. It's also recommended that buyers request a lab certificate that indicates nacre thickness and any treatments before making a considerable investment.

"There is nothing wrong with buying or selling pearls that are treated to improve color, luster or surface, as long as they are properly represented and appropriately priced," says Matlins. But, she warns, if they're too smooth, too perfect, too evenly matched, and priced dirt cheap, just walk away.

By Anne Sasso

© Colored Stone – May/June 2004

In association with