An Emeralds most unique and distinctive factor is its vibrant green. The most desirable colour is greenish blue with vivid colour saturation. As part of the beryl family, the colour has to be dark enough to be classified as an emerald. In the industry today there are many types of emerald treatments that can have positive and negative effects on the gemstone, which have consequences on the price, and can enhance specific properties. Emeralds have been treated for almost as long as they have been cut, the most common treatment used in the market is ‘fracture filling’. Commercial quality emeralds are inclined to have more internal characteristics than any other gemstone. The most common are surface reaching fractures and cracks, the reason being is that they are a brittle stone and the majority of emeralds are treated to improve their clarity and the overall appearance.
No oil Colombian emerald
An example of this is, an emerald can be treated with ‘Cedar oil’. It is natural oil that is colourless and also has a similar refractive index to the emerald and when heated in oil it improves the appearance of the fractures, giving it a clearer and more even appearance. This traditional treatment is, however, not permanent and re-oiling may be necessary depending on how much the emerald is worn. Artificial resins are also used, they conceal inclusions more efficiently and last longer. However this treatment is seen to have some long lasting negative effects. Over time some resins can dry out or turn brown or white, this makes the inclusion visible again. Being an artificial substance it is impossible to remove, making the stones' value drop dramatically in comparison to oil filled emeralds. The classification of the level of oil or resin in an emerald is broken down into:
Only a few gemmology laboratories differentiate between oil and resin fillings, but this differentiation is extremely important. We recommend SSEF (Swiss Gemmological Institute) and AGL (American Gemmological Laboratory), who both differentiate between oil and resin fillings.
Minor oil Colombian emerald
Additional treatments on the market include ‘dyeing’ and ‘coating’ emeralds, both of which should always be avoided. Dyeing is occasionally used to make a green beryl look more like an emerald, it intensifies the present colour and improves the colour uniformity. Surface coating alters a gem’s appearance by applying a colouring agent to the back of the surface of the gem. This will make the initial appearance of colour more even.
Untreated emeralds conduct premium prices, especially those from the now extinct Muzo mine in Colombia. An Old Mine Colombian untreated emerald can be up to 50% more valuable than an emerald with Minor clarity enhancement oil only, with the same apparent quality. An emerald with Moderate clarity enhancement can be about 35% less than a Minor treatment one. An emerald with Significant clarity enhancement should be avoided. In today's market more than 90% of emeralds have fractures filled with oil or resin. Therefore, extra care should be taken when cleaning and should not be cleaned ultrasonically or with steam. Vibrations can weaken already-fractured stones and hot steam can cause oil or unhardened resin to sweat out of the surface reaching fractures.