COUNTING FISSURES TO DETERMINE THE DEGREE OF
ENHANCEMENT IN EMERALDS
This one-page Summary is also written as an Eight-Page Article
After counting fissures on hundreds of emeralds, a close relationship (1:1) was found between surface-reaching fissures and the degree of face-up clarity enhancement.
When buying a car, one wishes to know how well or badly the previous owner treated it. With a trained, experienced mechanic that information is available. In buying emeralds, one wishes to know the degree to which the stone has been enhanced. Now that information can be determined with a microscope and a light source.
While air-filled fissures are highly visible, a fissure filled with transparent oil or some other suitable material will be less apparent; the stone will look cleaner. In emeralds, fissures are common and it is accepted in the trade for the visibility of such fissures to be reduced by traditional oils such as cedarwood oil and Canada balsam. For more information on the gemology of cedarwood oil click here.
LOOKING CLOSELY AT EMERALDS
It is necessary to view the emeralds in reflected incandescent light at 10x . The light makes the fissure openings appear as lines on the surface of the stone. Look for only the fissures that come to the surface; internal fractures will not improve. You have to count how many facets on the emerald have surface-reaching fissures and divide by the total number of facets to get your percentage. There is an easy short cut to estimating the degree of enhancement percentage: The average emerald cut emerald has either 37 or 41 facets; so just assume 40 and then divide in your head - 4 facets out of 40 is 10%, 6 out of 40 is 15%, etc. CATEGORIES OF IMPROVED APPEARANCE
These are the categories of the degree of visual improvement (viewed face-up) of the emeralds.
none 0-5% improvement of the overall face-up appearance
minor 6-20% improvement of the overall face-up appearance
medium 21-40% improvement of the overall face-up appearance
significant 41% or more improvement of the face-up appearance
When counting, the table facet must be weighted more than other facets like in diamond grading. If the table has several fissure openings it should be counted as 2 or even 4 facets rather than one. Remember that this is not clarity grading. Sometimes a very heavily included stone will only improve 3% because most of the fissures and voids are internal. Other times, a clean looking stone will have just one long fissure opening that permits a 25% appearance change.
One would naturally assume that the more surface reaching fissures there are in a gemstone, the more likely the clarity enhancement was successful. In general, almost 20% of all stones will show a 'negligible' degree of enhancement. This is a reflection of the good production in the last few years of clean bright emerald rough from the Muzo region.
Another general rule is that Medium or Heavy enhancements often have surface reaching fissures on both the crown and pavilion. Negligible and Slight enhancement stones often had surface reaching fissures only on the pavilion.
HOW TO BUY AN EMERALD
If you are buying an emerald from a trusted supplier and you have a good professional relationship with that person, ignore all treatment concerns and buy based on beauty. A person who consistently backs up his emeralds has obviously done the necessary studying of treatments and is buying cautiously and well. There is nothing better than a professional relationship that implies complete satisfaction with any stone sold- including buying back problem stones, fixing or recutting when needed. Millions of dollars of emeralds get sold this way every year and it is the oft-forgotten backbone of the industry. Lamentably, the only emeralds that get into the headlines these days are the 'problem stones'.
If you are buying at a trade show, discount house, or out of town and don't have a totally open relationship with the seller, then fissures must be counted and care must be taken to purchase only stones whose crowns are relatively free from surface reaching fissures. There is, in Bogotá, an exporter who exported 36,000 emeralds per year in 1995 and 1996. These were stones destined to be set in rings and pendants. This man's main criteria for buying was 'no cracks on the crown' and he hired a young person with good eyes to do only this type of quality control. The rate of returned stones as a result of this policy was 1/2 of 1% for two years in a row and many of those returns were from mistreatment such as re-sizing a ring with the stone in it! This is the lowest rate of returned stones in the industry and is a good vindication of the above buying method. In this age of high-tech gemological equipment and techniques it is reassuring to be able to have at one's disposal a simple test that can be done almost anywhere.
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