To those who are not aware, it should be told that all variants of emeralds come with intrinsic breaks and inclusions from nature. The key objective of treating an emerald is to fill in these breaks and treat them to diminish the flaws and render them more lustrous.
One of the ancient most practices pioneered by gemstone cutters was one that involved bathing the stone in natural oils. This ‘Oil Treatment’ of emeralds was useful in filling up the fissures of the stone and augmenting the appearance of emeralds. Using colorless oil is regarded generally an acceptable practice while application of green oil is regarded with suspicion. What happens actually is the breaks & fissures soak in the oil thereby softening the appearance of present flaws. Precisely due to this reason it is advisable to always steer clear from cleansing emeralds with ultrasonic cleaners and similarly soapy water should also be avoided.
In addition, clear resins like Opticon are also smeared on an emerald to seal down surface ruptures. As against the oiling technique, usage of Opticon gives longer lasting results. Opticon treatments are met with greater acceptability, excepting of course when green dye is applied to increase the colour of emeralds. In this context, one can hardly dismiss these April 1994 lines of Roy Albers, “Opticon is really bad, worse than a two-dollar bottle of wine: I will not buy emeralds that have been Opticon-treated; if all are thus treated, I would never buy emeralds.”
Of the key fillers used in filling the emerald fissures, mention may be made of Cedarwood oil, Clove oil, Canada Balsam resin, Epoxy 828, Opticon resin, Glass, Palma. All these fillers can be injected with vacuum pressure and have different refractive indexes, solvents, colors, evaporative and color stability. Opticon is evaporatively very stable in stark contrast to cedar oil. The evaporative stability of glass in emerald treatments is perfect, while that of Opticon resin, Epoxy 828 and Palma is excellent, Canada Balsam resin and Cedar/Clove oil take the good and poor slot respectively.
If we evaluate the color stability of resins/dyes used in emerald treatments, glass scores a perfect ten while Palma and Epoxy 828 are just average. Opticon takes on a yellowish orange hue with time especially upon heating. Cedar oil also yellows with age as clove oil treatments turn dark when exposed to light. Nothing is known with certainty about the color stability of Canada Balsam resin.
There are no clear-cut, well laid emerald treatment disclosure policies given the variety of practices and advancements in technology and obvious reasons. Still if you decide to go for a treated emerald, better to buy one that has a stable filling.