Gemmology Canada - Special Issue, 1995
by Janina Skawinska, A.G.
(C.I.G.), Winnipeg, Man
This relatively new process is designed to enhance the clarity of a faceted diamond by filling cleavages and fractures that reach the surface of the stone with a high R. I. material that helps disguise these inclusions. It is also one of the most controversial gemstone treatments to appear in the last decade! This treatment can potentially change the perceived clarity from SI to VS. An I quality diamond can be made much more desirable and saleable by this enhancement.
The first commercially available diamond fracture-filling treatment was developed by Mr. Zvi Yehuda, of Ramat Gan, Israel in the mid 1980s. This report will focus on the three main producers of fracture-filled goods. The companies are: Yehuda/Diascience, Koss & Shechter Diamonds (Genesis II) and Clarity Enhanced Diamond House (a subsidiary of Goldman Oved Diamond Company). More and more of these stones are now entering the market and the challenge of identifying filled diamonds and working with them at the goldsmith's bench is a reality to be dealt with. Besides the loose stones which were initially available, now fashioned goods are also readily obtained. This compounds the problem of identification further because mounts and settings can help to hide signs of treatment.
The Gemological Institute of America (GIA) first examined Yehuda treated diamonds in January 1987. The filling material was believed to possibly be either a type of glass or a silicone oil compound. What ever it was, it won't withstand all standard jewelry manufacturing or repair procedures. Boiling in sulphuric acid in a diamond boiling kit may remove all or part of the filling by using this cleaning method. Therefore, the durability of this enhancement is very questionable and disclosure is necessary from this point of view.
Gemstone enhancement is not a new idea! The concept of oiling emeralds, a practice that dates back to the ancient Roman Empire, is a treatment where air-filled fractures in gemstones are filled with transparent oil or some other suitable material making them less apparent. Diamond filling works on the same principle: replace the air that normally fills such breaks with a transparent substance that has a refractive index close to that of diamond. According to GIA testing, the refractive index of the filling compound is lower then the R. I. of 2.417 for diamonds, but is extremely close to it. The intended result is a much less visible inclusion that improves the overall appearance of the diamond to the unaided eye.
Process treated diamonds marketed by Yehuda Diamond Co./Diascience Corp., New York are first cleaned. The filling compound developed by Yehuda is injected into the diamonds at relatively high pressures (in the range of 50 atmospheres) and at a temperature of 400o Celsius. The exact procedure remains a secret and most likely involves the use of a vacuum to prevent diamond burning. The filled diamond is then cooled and cleaned again to remove the filling mixture from the stones' surface. The precise composition of the filling material remains Mr. Yehuda's secret but it is now known to be a type of molten glass.
Even less is known of the other two processes because they are relatively new procedures and little published information is available. However, the approximate temperature of treatment for the Koss process is estimated at 600o Celsius and between 500 to 550o Celsius for the Goldman Oved process.
The clarity improvement for all three treatment processes can be dramatic in stones with either small or large cleavages. Bearded girdles can also be treated. Occasionally there is no apparent improvement in the clarity after treatment. However, the treatment usually has a negative effect on the overall colour of the stone. In certain cases, a drop of one full colour grade is apparent.
With the unaided eye, a filled diamond may appear slightly greasy or oily with a very slight yellowish overtone. In stones with many treated areas, the yellowish overtone is most apparent. Examination of the fractures and cleavages with a microscope is the best means of positively recognizing the enhancement.
The presence of one or more of these features in a diamond provides evidence that the stone has been filled:
"FLASH EFFECT": One of the most common and obvious characteristics of a Yehuda treated stone. Filled breaks display a very yellowish orange interference colour in darkfield illumination that changes to an intense vivid "electric" blue when the stone is rotated very slightly to a position where the background turns bright through secondary reflection. When the treated diamond is tilted back and forth, the colour will change from orange to blue and back to orange again in a flashing manner. The flash effect was originally believed to be due to an interference mechanism It's now thought that the flash colours are due to dispersion instead.
The viewing angle must be very steep, almost parallel to the plane of the treated fracture or cleavage. The flash effect can be seen at low magnification with proper illumination. Diamonds with cleavage or fractures in the table-to-culet direction will display the flash effect easily through the table. Dark brownish yellow to orange diamonds will only display the vivid "electric" blue flash effect due to their body colour. In some treated diamonds, the flash effect is not visible in extremely small separations, such as a bearded girdle. Occasionally even a large filled fracture will not display any flash effect. Recently, in diamonds treated by the Yehuda process, a flash effect was seen along laser drill holes also. The flash colours in Koss stones are usually less vivid than those seen in Yehuda treated stones. Of the three products, the Goldman Oved treated diamonds have the most subtle flash effects.
The use of intense fibre-optic illumination, especially with mounted stones, may sometimes be necessary. The intense light from a pinpoint fibre-optic illuminator can make the flash effect significantly more noticeable as well as reveal the extent of the filled breaks and any hairline fractures in the filling compound. With mounted stones, where viewing angles are restricted, the flash effects can be noticed as reflections in the facets around the stone. In darkfield illumination, one or more of the following colours will be visible depending on the manufacturer: orange, pink, yellow, blue, purple and red (orange and pink being the most common). In bright field illumination: blue-green, green and greenish yellow are common. The red flash effect has only been visible in the stones treated by S & I Diamond Drilling.
Untreated diamonds which have cleavages and fractures that reach the surface may have a rusty orange coloured stain of naturally occurring iron compounds. This should not be mistaken for the orange "flash effect".
Untreated fractures in diamonds sometimes behave as thin films and display bright iridescent colours when viewed in certain directions. The rainbow-like colours and the feathery appearance of the cleavage itself will indicate that the gemstone has not been enhanced. The rainbow-like interference colours which can vary in intensity, should always show the same colour sequence with a broad range of hues. Flash effects display a single colour at most viewing angles or at the most two colours at a time. These iridescent colours in an unfilled separation are best seen at an angle nearly perpendicular to the plane of the break. The best viewing angle for a "flash effect" is near parallel (edge-on) to the break.
FLOW STRUCTURE: Another common and distinctive feature of the Yehuda enhancement process is the flow structure of the filling compound. The compound is forced into the exposed cavities at a high temperature in a molten state. The filling material flows by capillary action into any open areas in the diamond, masking the normal feathery appearance of fractures. Under magnification, the flow structures appear glassy and have an unnatural melted look. This feature was very subtle or absent from recent Yehuda and Koss treated stones. It is very subtle to fairly prominent in Goldman Oved treated diamonds. Use of fibre-optic lighting will be helpful with detection.
BUBBLES: Gas bubbles trapped within the filling compound are sometimes visible under careful microscopic examination. Occasionally, the bubbles are small but some can be quite large and obvious. In some areas of the material, the bubbles are so plentiful they form a fingerprint-like inclusion in Yehuda treated stones. Their formation is probably due to shrinkage of the compound during cooling and possibly from air trapped in the breaks by the liquified filling material. Bubbles are visible in both the Koss and Goldman Oved treated diamonds. Recent samples of Koss treated stones have exhibited larger and more numerous gas bubbles than in previous samples.
CRACKLED TEXTURE: A less common feature of the Yehuda enhancement process is a crackled or web-like texture in a surface reaching break. Similar to the mud crack seen in dry lake beds, this is visible only in the thickest portion of filled areas. This texture could be the result of a partial crystallization of the compound or rapid shrinkage as it cools. The appearance of this texture is conclusive proof that the stone has been filled. The crackled texturing hasn't been detected in Koss filled stones. In some Koss filled breaks there are extremely fine, nearly parallel whitish lines that seem to be minute fractures within the filler. The feature is subtle and can be seen only with the help of fibre-optic illumination. The crackled texture has not been observed in the Goldman Oved stones.
INCOMPLETE FILLING AT SURFACE: The Yehuda stones frequently show extremely shallow areas of incomplete filling at the surface. In darkfield illumination, these look like fine white scratches. The Goldman Oved diamonds have the same features. They are seen least frequently in Koss treated stones.
CLOUDY SURFACE/FILLED AREA: Yehuda stones sometimes have cloudy, circular surface markings, apparently residue from the treatment process. Recent stone samples have exhibited filling residue around the entry points of some filled fractures. None of these surface features were noticeable in any of the Koss or Goldman Oved treated diamonds. Recent Yehuda-treated diamonds also have areas of reduced transparency ("white clouds") in a few of the filled breaks. Less common, some cloudy areas are also visible in Koss treated stones. In many Goldman Oved treated stones, this feature is visible even before spotting the flash effect.
It is important to realize that not all of these described features will be found in every stone examined. No individual gemological feature or suite of features will conclusively identify which firm treated a specific stone.
The colour of the filling compound has also been studied. The Yehuda mixture seems to be light brown to orangy yellow in colour. The apparent colour of the compound would explain the usual lowering of the colour grade after treatment. The Koss and Goldman Oved treated diamonds don't display any inherent filler colour (although there is a drop in apparent colour grade in the Koss stones after treatment).
In August, 1987, Mr. Horiuchi of Japan, suggested in the International Coloured Stone Association's Lab Alert that the filling compound might be silicone oil. GIA testing disproved this theory for at least the Yehuda process and then later for the Koss and Goldman treatments.
Although this technique is not available to most gemologists, GIA decided to see if X-radiography could be useful in determining the presence of filled cleavages and fractures in a diamond. They used a technique similar to that used for pearls, but with a lower voltage and current because of the high transparency of diamond. The filled areas appeared much more opaque to X-rays than does the surrounding diamond. This technique sometimes does not reveal a filling as opaque on developed X-ray film and occasionally certain mineral inclusions appear opaque as well. This test is helpful as a preliminary assessment on large lots of diamonds. Detection by X-radiography depends on three factors:
1.The thickness of the filler.
2.The exposure angles (X-raying diamonds in at least two mutually perpendicular orientations to increase the chance of a filled fracture being detected).
3.Experimenting with film resolution and X-ray source intensity; thin or subtle fillings are more likely to be seen on developed film when lower energy conditions and longer exposure times are used.
All three types of fracture filled stones show "white" filling areas, some faint and others quite sharp when tested with X-radiography. There doesn't appear to be any correlation between the results of X-radiography and the strength of flash effects seen (a filled break that doesn't produce a distinct white area on the X-ray film may produce a pronounced flash effect under magnification or vice a verse). The filled areas of diamonds appear distinct white on X-ray film. GIA concluded that one or more atomically heavy, X-ray opaque elements were present in the filling compounds.
Further tests have been carried out by the GIA Gem Trade Laboratory (GTL) on the analysis of the filling material. Infra-red absorption spectroscopy in the mid-infrared range is generally used to indicate impregnation with an organic substance in other gemstones. These tests with infrared spectroscopy suggested that the filling material is not organic. Highly technical analysis using scanning electron microscopy indicated the presence of high-atomic number elements and also that the filling was not homogenous. The presence of lead and chlorine as major constituents was proved for the earlier Yehuda treated stones. Other elements were found in very small amounts - sodium, potassium, calcium, aluminum and silicon. Oxygen was also a major constituent of the mixture for all three types of processes. Boron, which is now usually present in all three fillers, cannot be detected by the EDXRF spectrometer.
Presently the chemical elements found in the various diamond fracture-filling compounds are:
Yehuda - Pb (lead), Bi (bismuth), B (boron), O (oxygen) and previously Cl (chloride)
Koss - Pb, Br (Bromine), probably Cl or O, may contain B
Goldman Oved - PB, Br, probably Cl or O, may contain B
When X-ray fluorescence was used on diamond samples, it proved to be a quick and effective technique for identifying filled diamonds. The instrument does not detect carbon, the bulk of a diamond's composition, but obtained readings for heavy elements comprising the filling agent. The Koss firm was reported to be experimenting with additives to make the filling easier to detect. However, no reaction - either to long or short- wave UV light was noted by GIA testers in the most recent round of testing.
Further testing by GIA using X-ray diffraction indicated that the filler was amorphous and probably a glass. Chemical analysis showed that the Yehuda material is a compound of lead, chlorine and oxygen with variable amounts of bismuth. The mixture is simply a lead-containing glass-like material. Various man-made "solder glasses" with high lead and bismuth contents have refractive indices in the two plus range. Chlorides of lead or bismuth typically have a high index of refraction. Their presence in the cleavages and fractures of a treated diamond would make these defects much less noticeable. Solder glasses are commercially available from large glass manufacturing companies such as Corning, Schott and Pilkington.
These glass-like compounds have low to moderate melting temperatures making them attractive for a process that requires that the filling material be drawn into breaks while it's in a liquid state. The compounds mentioned above have an intrinsic yellow to red coloration. This would account for the slightly yellowish tint of the filling material and the consequent drop in colour grade of diamonds after treatment.
An important issue of any gemstone enhancement is durability. GIA conducted numerous tests to determine the durability of these treatments under conditions which a diamond might be routinely subjected. Diamonds are commonly cleaned in an ultrasonic cleaner using a solution of commercially available jewelry cleaner. The Yehuda compound seems to be unaffected by this method of cleaning. While ultrasonic cleaning for a brief period may not damage at least some fillings, extended or numerous cleanings of short duration may cause some damage to the filling compound.
Steam cleaning is used on diamond set jewelry to remove gold polishing compound and other debris that has been trapped in the mounting during manufacture or repair. GIA tests with steam cleaners for a period of 20 minutes also showed that the treatment was not affected for the Yehuda treated stones. Both Koss and Goldman Oved stones showed areas of damage after steam cleaning only briefly.
Occasionally, jewelers will boil diamonds in a solution of water and detergent. Boiling of treated diamonds for 30 minutes by GIA researchers also showed no ill effects on the filled areas.
On the other hand, boiling in sulphuric acid to remove dop, prong and tweezer metal and to clean out laser drilled inclusions did damage the Yehuda compound according to Rapaport Diamond Report, 1987. Also the heat generated during a repolishing procedure had previously been reported as causing damage to the treated areas. Repolishing produced different degrees of damage to the filler in all three types of treated stones.
Of great potential concern, independent research has shown that extended exposure to a short-wave ultraviolet lamp (and by inference, to prolonged daylight exposure) can cause degradation of the filling material in both Koss and the Goldman Oved treated diamonds. The material showed discoloration and clouding after only 100 hours under a long-wave UV lamp. The presence of Br in the Koss and Goldman filler may explain this durability problem.
GIA also subjected the treated stones to rapid cooling using liquid nitrogen. The thermal shock didn't seem to damage the enhancement.
A diamond undergoes great stress during setting and also during the retipping of prongs when being repaired. When GIA staff set treated diamonds in a gold cast four prong head using standard pressure no ill effects were noticed when care was taken not to place a prong directly on the filled area. However, when retipping progressed with the stone being preheated slowly to bring it up to soldering temperature, it became a dark bright yellowish green. Each time the stone was heated and air cooled, it changed back to its original colour. The filling had been damaged after retipping. Beads of the Yehuda compound had sweated out of the cavity and were visible as tiny droplets along the surface. The conclusion of this test was that treated stones should never be in direct contact with the heat of a jeweler's torch. For all three types of treated diamonds, the heat from retipping tests caused major damage to the filled fractures. Careful resizing (when the jeweler is aware of the diamond being fracture filled) caused no damage to any of the three types of stones tested.
Diamonds which have filled cleavages or fractures are considered to be in the same category as coated diamonds for grading purposes by the GTL. A coated diamond must have the coating removed before accurate grading can be done. The same applies for a filled diamond. In neither case can the true colour of the stone be determined with the enhancement still present. There is no practical method to remove all of the filling compound to make this assessment.
Laser drilling is a permanent, stable procedure that attempts to enhance the clarity of a diamond. A filled diamond is especially unstable when exposed to high temperatures and cannot be considered a permanent change in clarity. Laser drilling doesn't effect the colour of a diamond, only the clarity. While the filling procedure may produce a significant change in colour equivalent to one full grade in many stones. The present policy of the GTL is to not issue grading reports on any diamonds that contain any form of filling. The GTL will only issue a document stating that the stone in question is a diamond and that it has been filled.
Although there is nothing inherently wrong with any enhancement process, full disclosure should always be made at every level of sale. Because of industry concerns about detection and disclosure, it has been suggested that all stones be laser inscribed with initials that disclose the treatment. At this point in time, this procedure has not been adopted by the manufacturers. In 1989, members of the International Diamond Manufacturers Association (IDMA) and of the World Federation of Diamond Bourses (WFDB) passed resolutions declaring that "knowingly selling diamonds treated by this method without disclosing that fact is a fraud and conduct not becoming to a member."
During the biannual congress of the IDMA and the WFDB in Antwerp in June 1993, diamond treatments and their proper disclosure was a major focus of discussions. The Diamond Club West Coast in Los Angeles issued a statement asking all major grading labs not to grade filled diamonds. A similar resolution was passed by the IDMA and WFDB in Antwerp in June 1994. At this latter meeting, a resolution passed that prohibits the filling of rough or the selling of filled rough. The Diamond Manufacturers and Importers Association has asked the trade to refer to them as "treated" rather than "enhanced".
The International Confederation of Jewellery, Silverware, Diamonds, Pearls and Stones (CIBJO) has warned jewelers of their potential liability if they do not disclose to customers both that a diamond has been fracture filled and that there may be durability problems. Well known U.S. retail chains such as Zale Corp., Sterling, Carlyle & Co., Karten's Jewelers, and Helzberg's and Suberi Brothers (a manufacturer) have notified their suppliers that they won't accept filled diamonds. The Independent Jewelers Organization has asked its member suppliers not to sell fracture-filled diamonds.
Promotional material from both Yehuda and Goldman now offer a "lifetime guarantee card" with the purchase of one of their treated diamonds. If anything should happen to the filling compound in their treated stones, the diamond will be treated again at no additional cost. With claims of price reductions of up to 60% below "similar untreated diamonds", these companies will continue to secure a firm foothold in the jewelery industry for the price conscious consumer. This enhancement method is becoming more common each year. Large parcels of filled diamonds have been reported by members of the trade. Unfortunately, several clients were unaware their stones had been filled before testing by GTL.
An expose televised locally in August and September 1993, accused two St. Louis jewelers of selling filled diamonds without disclosing the treatment to customers. This created a public concern about fracture filling when the show was broadcast nationwide on Prime Time Live and then addressed by a member of the U.S. House of Representatives. Australia and the United Kingdom have also had problems with instances of filled diamonds being sold without proper disclosure.
The fracture-filling process does improve the appearance of diamonds that before treatment were likely not marketable as jewelry-quality stones. It also acts as a sealant, preventing dirt or other debris from entering laser drill holes and other open breaks in a gemstone. The improvement in apparent clarity is usually one grade and sometimes two grades. Some diamonds with large treated areas exhibit a drop in the colour grade due to the colour of the filling material; however, no apparent drop in the colour grade was noticed in the Goldman Oved stones.
The filling treatment process has grown from being widely used on diamonds in the colourless to light yellow range and it is now also being used on fancy-coloured diamonds. Many jewelers still don't regularly examine diamonds for signs of fracture filling. There are recent estimates that 20-30% of the diamonds sold in the U.S. today are treated. Dror Yehuda indicates that "tens of thousands" of diamonds treated by his family's firm were already in the U.S. market. The larger size filled diamonds on the market appear to have been treated by the Yehuda process. Ron Yehuda states that his family's firm prefers to treat stones larger than 0.25 ct and that most stones treated are over the 0.50 ct mark. Over half the demand is for stones over 1 ct and these stones are marketed primarily in the U.S. and Canada.
Genesis II - Enhanced Diamonds Ltd., in New York, a division of the Israel based firm Koss & Shechter Diamonds Ltd., offers "clarity- enhanced diamonds" under the trademark name Genesis II which was first introduced in Australia. Daniel Koss, Managing Director, reports that in a three year period his firm has treated over 500,000 stones from 0.01 to 50 cts.
Clarity Enhanced Diamond House, a division of Goldman Oved Diamond Company, New York, offers treatment services and also sells treated diamonds. The process is preformed in both New York and Israel. Goldman Oved has enhanced stones in the range 0.02 to 15.5 cts.
Besides the three main firms, Chromagem of New York, operates a smaller scale shop selling filled diamonds that have been treated by an independent chemist. S & I Diamond Drilling of New York provides filling services to the diamond trade only. In Los Angeles, Diamond Manufacturers are treating diamonds. Wholesale firms market to the retail trade (under their own trade names) diamonds treated only by others. For instance, Doctor Diamond, a division of Kami & Sons, New York market "Doctor Diamond clarity enhanced diamonds" which include diamond treated by both the Yehuda and Goldman Oved firms.
Koss claims that its' filled diamonds exhibit little or no telltale flash effects and the colour of the treated diamond is unaffected by the filling compound. A promotional brochure from Koss states that cracks disappear completely, with no bubbles trapped inside the filler. They further claim that rays of light travel through the diamond "with no distortion or deflection whatsoever". Koss also states that their clarity enhanced diamonds withstand temperature to 450 degree Celsius, acid-based cleaning and "ultrasound treatment". Research findings by gemologist Sharon Wakefield of Boise, Idaho, indicate that the filling material used in the Koss process may decompose when exposed to a short-wave ultraviolet lamp or ultrasonic cleaning.
The technology for fracture filling of diamonds continues to evolve as producers try to improve their process. Koss is using two process treatments currently. One process is based on halogen glasses (the commercial treatment presently used) and the other is based on experimental halogen-oxide glasses.
It will certainly be challenging for the gemmologist and the jewelery industry to try and keep up-to-date on these gemstone enhancements in the years to come.
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Koivula, John I. and Robert C. Kammerling.  What jewelers should know about fracture filled diamonds. 25 min. videotape + 13 p. booklet.
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Yehuda, Ron.  "Yehuda responds to media attention with Flash Effect educational aid." News from Yehuda Diamond, Spring 1995, p. 1-2.
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