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Emerald Enhancements and Treatments
As a well-known dealer in many varieties of fine gemstones, we are often asked why we carry so few emeralds. The answer, sad to say, is that it has become harder and harder to find high quality emeralds that have not been heavily treated.
Emeralds tend to be among the most included of all natural gemstones. The inclusions are tolerated because the finest emeralds display a vivid bluish-green color that is quite unique in the gems world. But in many cases the various internal gas bubbles, embedded crystals, veils and cracks make the emerald look cloudy or milky.
It has long been known that emeralds can be oiled to improve their appearance. Because most emeralds have tiny fissures that reach the surface of the gem, it is possible to fill internal inclusions by forcing oil through the surface-reaching fissures. The result is improved clarity since the light performance of the filled cracks is similar to that of natural emerald.
The traditional treatment for emerald is fracture-filling with natural oils. Cedarwood oil is most commonly used, because it is colorless and has a refractive index close to emerald. But the oil can dry out and emeralds have to be re-oiled from time to time to keep them looking their best. Because the oiling process requires heat and pressure to force the oil into the gem, it is not a trivial matter to maintain an emerald.
Emerald producers have searched for a more permanent solution. The Brazilians were the first to begin using a synthetic resin known as Opticon in the 1980's, and were followed in this practice by the Colombians in the 1990's. Opticon, an expoxy prepolymer, has better stability than cedarwood oil, and a refractive index almost identical to emerald. But many stones that were treated with this new resin came on the market without disclosure, and dealers and buyers became especially nervous when it was discovered that some emeralds had been treated with colored Opticon.
Since Opticon-treated emeralds reached the market, many other polymer fillers have been used to enhance emeralds, including Gematrat, ExCel and Permasafe. Gemological labs are still trying to classify these fillers and understand their stability and long term performance.
Since emeralds may be enhanced to a greater or lesser degree with these fillers, gemological reports usually indicate the level of clarity enhancement for emerald, ranging from None to Insignificant, Minor, Moderate and Significant. If moderate or significant enhancement is detected, a lab will try to identify the specific filler used.
The profileration of enhancements for emeralds has resulted in a loss of trust in the emerald market and led to questions about the value of emeralds treated with these new fillers. Given the market situation we prefer to deal only in untreated emeralds.