Assume that all emeralds have been oiled.
Make sure treatments are clearly stated on your bill of sale.
Get a professional appraisal only if you are purchasing a very expensive stone.

Emeralds are about the only gemstone that is not heat treated for color enhancement. However, it is one of the most visibly flawed stones on the market. So, how do dealers enhance the stone for sale and disclose the treatment without turning off a prospective client, who wants a naturally beautiful stone, while revealing the work that’s been done?

Almost all emeralds have surface cracks, pits and other blemishes that mar the overall appearance of the gem. If the crack begins on the surface and reaches into the stone, it can be filled with either a color enhancing oil or an epoxy filling. Both treatments are not permanent and have their drawbacks.

1. Oil fillings hide cracks very well and improve overall color, but the oil wears away in a fairly short period of time, leaving a noticeable brownish or whitish residue. The good news is the residue is easily cleaned away and the stone can be re-oiled. This is the preferred method of color enhancement, as long as the oil is colorless. The use of green colored oil is considered unethical.
2. Epoxy fillings, although far more durable than oil treatments, have proven to not offer the solution to the lack of permanence of oiling that was once hoped for. The problem is that, although, the treatment lasts much longer than oiling, the epoxy will eventually dry up, leaving the same residue as the oil, but impossible to clean and re-treat.

Until a new material is discovered that can permanently fill the cracks common to emeralds, oiling is the method of choice at this point. And it is a perfectly acceptable treatment, as long as there is full disclosure. Which brings us to the bigger issue:

Full Disclosure: Most gem dealers are highly ethical professionals, but there are the occasional bad apples who will try to pass off treated stones as natural. You need a professional appraiser to tell the difference, so if you are just looking at a relatively inexpensive stone, don’t bother. If, however, you are considering a very valuable emerald, by all means have it checked out by a pro before plopping down thousands of dollars. The only thing you can do is to look for cracks on the surface of the stone. If there is no break on the surface, there is no way for oil or epoxy to enter the stone. It is best to assume that all stones have been oiled for clarity enhancement. This becomes an issue in exact proportion to the amount of money you are about to spend on your emerald. Remember, though, that the law requires dealers to disclose all treatments. Therefore, don’t be afraid to insist that disclosure of such treatments be clearly stated on your bill of sale.

Answer to quiz: b & c