The enhancement and treatment of colored gemstones has existed for centuries. While some treatments improve on the natural gemstone only slightly and are scarcely detectable, others produce dramatic changes and can permanently transform nature’s intent into seemingly perfect, marketable, stones. Not all colored gemstone treatments are without issue, and some can be particularly problematic and even deceptive. Pearls, Coral, Jade, Lapis Lazuli, and Turquoise share some kinds of common treatments, but knowing the difference between accepted practices and potentially deceptive ones is key to understanding the colored stone’s true value.
Treatments for Pearls and Corals
Pearls are a naturally occurring product of shelled mollusks. Technically composed of concentric layers of calcium carbonate, ideal gem quality pearls are perfectly round, smooth, and iridescent, with a thick, nacreous outer layer. Naturally occurring pearls are extremely rare—the majority of pearls currently sold are cultured pearls, specifically cultivated for jewelry. While the highest quality cultured pearls may only be cleaned and polished, most other pearls are subjected to treatments to enhance their beauty. Corals are also a naturally secreted substance—the hard, bony external skeleton of certain coelenterates usually found as reefs in warm, tropical seas.
Bleaching is by far the most common treatment for coral and pearls, being used to lighten, change, or even-out color. In pearls, the first layer over the nucleus is conchiolin, a dark protein. Bleaching can lighten this layer, especially when the nacre is thin. Bleaching is common for all but cultured South Sea pearls, and cultured American freshwater pearls. Corals are often bleached to enhance uniformity of color.
Polishing is another common treatment for pearls. Some pearls are simply tumbled with natural materials in an oily medium to enhance luster. But occasionally, cracks or pits are filled with epoxy or other resins. Pearls treated in this way are easily detected and of little value as gems.
Pearls and corals are sometimes dyed to provide markets with colors that are rare or as a way to create a matched strand of pearls. Dyed pearls are typically lower-priced than comparable untreated pearls. While simple bleaching is a generally accepted practice, dyeing, especially in coral, is often used to disguise poor quality goods.
What is commonly referred to as jade is actually two distinct minerals—jadeite and nephrite—with different chemical compositions, densities, and levels of hardness. Jadeite is generally much more valuable than nephrite, with the very finest jadeite referred to as imperial jade.
Bleaching of both jadeite jade and nephrite has become prevalent as a way of removing brown pigments, though bleaching can cause jade to become porous and weaker. As a result, bleached jade is usually impregnated with a polymer that fills the fractures and strengthens the stone.
As with most all colored gemstones, untreated jade is more valuable than treated jade, and the greater the degree of treatment, the lesser the value of the gemstone. In a classification system that originated in Hong Kong, jadeite that has been treated in the two step process is often referred as “B” jade. “A” jade refers to jadeite that is natural or only treated with wax, and has not been bleached or resin filled. “C” grade jade refers to jadeite that has been bleached, and the resin used to fill it has been colored by dye to enhance the gemstone’s color. Though various tests can detect some of these treatments, a certified lab using infrared spectroscopy is the only way to conclusively determine the degree of polymer impregnation in jade.
Treatments for Turquoise
Turquoise in its natural state is relatively soft and porous—there is actually very little hard, “natural,” gem quality turquoise available. Because of its inherent weaknesses, most turquoise is treated to enhance its stability. Ancient treatment techniques involved waxing and oiling, but modern “stabilized” turquoise refers to turquoise that has been treated with a clear resin that fills the porous surface, both strengthening and sealing the colored gemstone, allowing the treated stone to be cut into various shapes and polished.
“Pressurized impregnation” is another kind of stabilization process, wherein a resin is forced deep into the turquoise with high pressure, often with colored dyes. Any turquoise that has been color treated should be identified as such, and priced lower as a result.
Treatments for Lapis Lazuli
Lapis lazuli, commonly referred to simply as lapis, is typically not treated or enhanced, though occasionally some lighter stones can be dyed to result in deeper blues. Dyed lapis may also be coated with plastic resin or wax to improve its stability, or impregnated with colored material to improve its luster and color. These treatments are usually applied merely to disguise poor quality materials and are fairly easily detected.
Where to Sell Expensive Gemstones
If you are looking to sell estate jewelry set with high quality pearls, coral, jade, turquoise, or lapis, contact Diamond Estate Jewelry Buyers today. We are widely recognized as the best place to sell expensive gemstones in the country. Our gem buyers specialize in antique colored gemstone jewelry, as well as estate jewelry from Van Cleef & Arpels, Cartier, Tiffany & Co., Chopard, and other luxury brands.