Almost every emerald available on the market has been treated to improve its clarity. Because emeralds are naturally full of cracks and fissures which make it more opaque and less attractive, it has become an industry standard to fill the cracks in emerald, thereby improving its clarity. Traditional fillers are natural oils such as cedar oil. Over many decades, these oils may fade or "sweat."
Although they are accepted and do not make an emerald worth less, there is discussion regarding the permanence of the treatment. (For a gemstone treatment to not diminish a gemstone's value, it must be "permanent." See General Gemstone Information.) Other methods of filling cracks in emerald are bing explored such as waxes, resins and even glass. A substance is considered good for filling cracks in emeralds when it reflects light in a way very similar to emerald, thus making the fillings less noticeable.
While filling cracks is acceptable for improving clarity, sometimes it is also used for improving color. For example, green dyed oil is used. This is generally considered deceptive and it is better to not buy these "dyed" emeralds. This can be detected under 10X magnification.
|Dyed: This may be an example of an emerald that has been treated with dyed oil to improve not only its clarity but its color. The clue is that all the cracks are the same, distinct color from the rest of the stone||Treated Emerald: This is an example of an average quality emerald that has been treated by filling cracks with oil or resin. We cannot tell the difference, and we don't need to because it doesn't hurt the value.||Created: Here is a very clear emerald. Though it does have some large inclusions, the absence of "milkiness" and the very bright geen color are hints that it is synthetic. An emerald like this is very rare to find in nature||Created: A perfectly clear emerald. When you see an emerald this clear (no inclusions at all), you can be certain that it is synthetic,|