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May 14, 2015
EMERALD BUYING GUIDE: WHY FISSURES IN EMERALDS ARE FILLED-IN AND HOW THIS AFFECTS THEIR PRICE
To understand why the fissures or the cracks in precious stones are filled, we first need to understand the effect that fissures have on gemstones.
But before this I am going to explain a very important concept to you about gemology: THE REFRACTIVE INDEX.
The refractive index (also called the index of refraction) of a gem concerns the relationship that exists between the speed of light in a vacuum (whose index is 1) and the speed of light through the gem. The denser the gem, the lower the speed of light in that medium and the higher its refractive index. Usually gems have a RI from 1.2 to 2.6.
But now let's get back to fissures; certain gems, such as emeralds, usually present quite a few inclusions, and inside these inclusions we find fissures and/or cracks that can break through to the surface, and then, what happens to light? This is when what we call reflection takes place. Light meets two different mediums; in one it travels at one speed, and in the other at a different speed; and the difference is so large that it becomes very visible.
Air is introduced into the fissures that reach the surface, and in these areas the light will appear dimmer, bringing down the color of the gemstone considerably. And how is this corrected? By introducing a refractive index into said FISSURES - an ELEMENT that is as similar to the gem's index as much as possible, to minimize the effect, and in this way, the color saturation is increased. In cases where emeralds have many cracks, this will not only give them a better color, but also greater stability.
The words ELEMENT and FISSURES are written in capitals. And they play an extremely important role in the commerce of emeralds. Because the economic value of the emerald will depend on the type of filler used and of the number of fissures that require filling.
There are treatments that are accepted, others that aren’t, and then there are 'treatments' that are not really treatments, but a hybrid of synthesis in gemology (we mean, they are more “manmade” than made by nature).
Emeralds are treated in 99% of cases, that is, it is an exception when they are not treated. In these cases emeralds reach extremely high prices.
The most accepted treatment in the business is to fill or impregnation the fissures with COLORLESS oil. This treatment is reversible. With time the oil progressively disappears.
The less accepted and most economically penalized treatment is dyeing, which is a variant of impregnation, it is used on gems that have very little color and many fissures and/or cracks, and it consists of introducing an oil or resin into the fissures with a green coloring additive to potentiate its color. It can be reversible or not (depending on the type of filler). Emeralds that have low economic value due to their color generally then have a green color that is quite attractive to the client.
The fillers can be made using other substances like resins, polymers, (Epoxi, Gematrat, ExCel, Palma resin, Opticon, PermaSafe, Joban, etc.). In some cases the filler is made of the same composition that the emerald itself has, adding nanodiamonds to give them greater hardness.
The GIA establishes another parameter to take into account, and that is the amount of filler in the FISSURES. It establishes three levels:
Minor: Small amount of filler
Moderate: Higher amount of filler
Significant: Large amount of filler
Clarity enhancement as classified by GIA. These images were taken from the report entitled Gems & Gemology Winter 1999 issue. (Photos were taken by Maha Tannous).
The treatment of emeralds is quite complex, not only because of its variety, but also for how this treatment affects the price of the emerald. A gem, of the same size and color, can be worth some thousands of dollars or just a few, and the difference lies in whether the filler of the fissure is colorless or not, on the type of filler, and how much filler was required.
As always my advice is: Request a GEMOLOGIC CERTIFICATE from an independent laboratory.
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December 04, 2023 1 Comment
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