A Primer

The inclusions in emeralds are often extremely fine gas pockets or fissures. The difference in refractive index or “light bending” between the emerald material and the air in the fissure makes the fissure visible. To disguise the fissures, numerous materials have been used to fill them, and if the refractive index of the filler is similar to that of emerald then it makes the fissure less visible.

Considerable discussion has developed over the different materials used for this purpose, be they oils or resins or waxes, either “natural” or man-made. The Gemological Institute of America has suggested that the terms “natural” and “synthetic” not be used in this regard. They suggest that “presumed natural” be used for all substances that are naturally occurring, because in many cases these essential oils, other oils, resins and waxes cannot be distinguished from the same materials made in a laboratory. At the same time the GIA suggests that the “synthetic” be avoided altogether, because it has a very different meaning in chemistry than in gemology. The GIA suggests using the term “artificial resins” for all prepolymers and polymers that have no natural equivalents. The names of these artificial resins that you might find reference to as emerald fillers are Opticon 224, Araldite 6010, and others.

There are several issues involved here, including the durability of the material used as a filler, discoloration, specific effects caused by the filler, and tradition or customary use. From a legal point of view, full disclosure of any treatment or enhancement that is known to have been used or detectable by technical means may be sufficient. However, in the Colombian emerald trade there is a clear distinction between the use of presumed natural essential oils, particularly cedar oil, and the artificial resins. There is also discomfort on the part of traditional emerald dealers regarding the use of “palma”, presumably a natural palm oil, which is very close to the refractive index of emerald. In the latter case the concern is centered about the fact that this oil can produce “flash effects” in the fissures which under some circumstances makes the fissures stand out, and at the same time that this oil masks the fissures too well, and thus is considered deceptive.

Cedarwood oil is the traditional clarity enhancer that has been used on Colombian emeralds for generations. Its use is very wide spread, not to say ubiquitous, in the Colombian emerald trade. Cedar oil provides clarity enhancement while at the same time not hiding the fissures completely, and thus allows the buyer to detect their presence. Also, cedarwood oil is quite stable and remains in the stone; and in the thin films that are formed inside the fissures it is color-stable as well.

If you wish to be completely sure that an emerald you buy has received no clarity enhancement you need to look carefully at the stone with a loupe. If the stone is perfectly clear, that is to say that the material is compact and perfectly formed with no inclusions, then there are no fissures within it to accept any type of filler. Also, if fissures are present but they do not reach any of the stone surfaces, then likewise there is no way for a filler to have found its way into the stone.

My policy is to accept cedar oil as a clarity enhancer, and to reject all other enhancement methods if detected. In addition to the observation of stones, my best strategy for avoiding clarity enhancers has been to arrange to facet my stones directly from rough emerald crystals that have been bought at the mines. This provides total assurance, for the cutting process will reveal the presence of any treatment given to the emerald crystal or “rough” as it is commonly referred to.