Recent advances in technology have contributed to many new pearl treatments during the last decade. Like more traditional enhancements to pearls, some of these treatments are accepted by the industry. However, some treatments – which are generally undisclosed and often quite difficult to detect – are not accepted.
If you are shopping for pearls, here's a summary of known pearl treatments being performed today. Several of these treatments may be used in conjunction with one another in order to produce the most attractive (and expensive) gem possible. Also, do remember: the very best pearls do not require treatments. The goal of any treatment is to mimic colors and other fine, rare characteristics that are most coveted and valued in top pearl specimens.
Heat Treatment for Pearls is Difficult to Detect
The Fall 2010 issue of the Gemological Institute of America (GIA) publication, Gems & Gemology, presents an overview regarding pearl treatments in use today. In their article "Gemstone Enhancement and Its Detection in the 2000s," Shane McClure, Robert Kane and Nicholas Sturman, report that thermal enhancement to pearls – sometimes used on cultured pearls in order to change appearance – remains difficult to detect.
So far, UV fluorescence reactions and UV-Vis-NIR spectroscopy are the only "useful" means to detect that pearls may have been heat-treated. The authors report that although heat alone often produces pearls with more saturated yellow colors, "other effects can result when heat is used in combination with other methods," including bleaching, as in the case of brown pearls.
Irradiation Alters Trace Elements in Pearls
Exposing gems to radiation such as electrons, gamma rays and neutrons, often induces intense colors. In the pearl industry, irradiation has been used for decades, although it continues to be quite difficult to detect. The enhancement is almost always associated with the nacre layers in freshwater pearls or nuclei darkening in Akoya pearls. Highly valued colors of gray, sliver-gray, and black are produced as the result of radiation.
Coatings Improve, Hide and Protect Pearl Surfaces
Surface coatings have been around forever. With pearls, coatings are often used to improve surface luster, mask imperfections and/or offer protection from harmful chemicals. Since 2000, several new coatings have been used with pearls. One development, the application of DLC coatings to improve durability, should be carefully monitored, according to McClure, Kane, and Sturman.
Sometimes, thin, plastic coatings may be used to make pearls look like pricey, dark, Tahitian pearls. Reportedly, such coatings offer a different feel and may produce surface "bald spots" due to uneven wear. These types of coating are not accepted by the trade.
Some Dyed Pearls Mimic Expensive Black Pearls
Used since ancient times, dyeing is used to improve the surface appearance of gems. With pearls, dyeing – often with silver nitrate – is routinely used to improve the looks of lower-quality natural and cultured pearls. Most dyed pearls are natural, however, dye is also used to make non-porous imitations look more real.
In 2007, during a Gemstone Gathering presentation in Thailand titled "The Identification of Rare Pearls and Pearl Treatments," presenter Ken Scaratt, Director of GIA Research, Thailand, said that some dye-treated pearls may be identified by color concentrations on gem surfaces "particularly in the areas of blemishes and the entrances of drill holes." Moreover, Scarratt demonstrated how silver nitrate dyeing could be discerned through reversal of growth structures on a microradiograph and/or chemical analysis.
Silver nitrate has been in use at least since the end of the 19th century to darken natural pearls to produce silver, black, grayish or brownish colored pearls. In this method, pearls are soaked in a silver nitrate solution for a period of days to weeks, then exposed to a strong light source or treated with hydrogen sulfate.
Pink Pearls, Golden Pearls, Peacock Pearls may be Results of Dyeing
Since 1990, cultured pearls dyed to resemble pricey, natural golden pearls have been of concern to the industry. These impostors of very expensive and rare natural goldens can be difficult to identify because it may take chemical analysis to detect trace elements, like iodine, that indicate treatment.
In addition, natural, white and cream pearls are sometimes dyed to give them a desirable pink tint. The pink coloration is often barely perceptible. Pink coloring is generally accepted in the trade, as long as the color is permanent, appears to look natural, and is not discernible around drill holes.
Also, chemical whitening compounds in freshwater non-beaded pearls and metallic dyes injected into pre-harvested pearl sacs, as well as a dyeing process marketed as "lasering" (which produces coveted dark peacock green or dark purple colors) are in use.
Pearl Fillers Cover Surface Flaws
Scarratt also talked about how pearls with large surface voids may be treated by filling the areas with a variety of substances, including wax, wire, and metal balls. He said these treatments may be observed in micoradiographic images.
Sometimes, low-quality, cultured, baroque pearls are filled with epoxies if they are partially hollow or have a loose nucleus. Experts report that his treatment helps the bead nucleus remain intact when pearls are restrung as jewelry and that it makes the pearls more durable overall. Filling a hollow, natural, pearl brings it close to the expected weight for a normal pearl of that size, reports Stephen Kennedy of Great Britain's Gem Testing Lab, during the 1998 American Gem Association Symposium. This is particularly significant because natural pearls are often sold by weight.
Pearl Bleaching – Acceptable and Almost Impossible to Prove
Bleaching has long been considered an acceptable pearl enhancement that results in pearls looking whiter with a more even color. According to the Gems & Gemology article, the treatment is difficult to detect due to the fact that it is nearly impossible to prove a pearl's exposure to bleaching agents such as hydrogen peroxide. Improper bleaching may lead to softening of the pearl nacre, making it less durable.
In fact, all types of pearls are routinely bleached to some extent, including natural, bead cultured and non-bead cultured. Moreover, Akoya cultured pearls (originally from Japan, now produced in great quantity in China) are regularly bleached and then "pinked." By contrast, freshwater pearls from the United States, and light-colored South Sea pearls are not usually bleached.
Bleaching is a key component in the propriety process used to produce brown, or "chocolate" cultured pearls which were introduced to the market and became very popular since the turn of the century. Although brown pearls may occur naturally, they are extremely rare. The bulk of pearls marketed as "chocolate" today are treated to achieve their colors.
Pearl Luster Enhancement is Common
When it comes to pearls, luster enhancement has two meanings. First, it involves a substance, like beeswax or some sort of chemical polish, that is rubbed or buffed onto a pearl's surface to improve appearance (this type of treatment is common to jade as well). The waxy substance remains on the surface and does not impregnate the pearl.
However, it is possible for the wax to wear off. Also, chemicals may damage the nacre. Luster enhancement without chemicals is acceptable when performed in order to surface-clean and/or remove minor scratches.
The second type of treatment was developed recently, and is specifically for pearls. In order to improve the pre-polishing process. According to the Gems & Gemology article, special solvents are used to "clean" the surface nacre of pearls to obtain more luster. The name "Maeshori" is associated with this type of treatment, although other types of this kind of treatment exist.
McClure, Kane and Sturman say that polishing occurs during all steps of the pearl supply chain. Polishing is used on all types of nacreous and non-nacreous pearls as a way to improve appearance and desirability. Pearl farmers often tumble cultured pearls with walnut chips and/or other materials before polishing.
Claire Eddins - Writer/editor, award-winning photographer Claire Eddins collects gems, horses, and obsesses over home, art, and design.
