What is fracture-filled diamond?
There are many diamonds (both loose and mounted stones) that come across my desk on a daily basis for inspection as a part of the appraisal process. One of them is this diamond. It is an otherwise I3 in clarity before treatment (I3 is the lowest clarity grade in the GIA diamond grading system that I3 diamonds are highly included by fractures, crystals and other types of inclusions). By the time I graded this diamond under 10x magnification, it is considered by myself as I2. What did they do to this diamond to enhance its clarity?
As you see in this magnified image (60x), there are blue and purple flashes at the areas where the fractures were. They are indication of fracture-filling. It is a common treatment in the diamond trade, to introduce fillers that have their refractive index close to that of the host stone (in the case of the diamonds it is 2.417), so that when white light enters the gem it will not be disturbed, and the fractures will be virtually invisible (at least to the unaided eye).
There have been several research and reports regarding this treatment, it was suggested that the filler material was a compound containing lead, chlorine, oxygen and bismuth, which was injected into the stone under pressures of about 50 atmospheres and temperatures around 400 degrees Celsius. Other companies who work on this were reported to be using higher temperatures. A report by the Gemological Institute of America (GIA) noted that a vacuum chamber may be involved. Later, it was reported that alternative filler materials involved silicone-type substances.
Are fracture-filled diamonds permanent?
Research and experiment have shown that fracture-filled diamonds can be relatively stable under normal handling conditions. However, when the diamonds are placed under certain types of stress, the treatment can be reversed. For examples, the heat from the torch of the bench jeweler when repairing the jewelry that contains fracture-filled diamond, or boiling fracture-filled diamonds in sulfuric acid, which is a process sometimes used to remove metal remaining from the manufacturing process from the surfaces of rough girdles… could damage or remove the fillers, therefore returning the diamonds to their previous state, which are cracked and full of fractures that could affect their durability and of course, reduce their clarity grades. Of all other factors (color, carat weight, cut) being equal, a lower clarity grade diamond has lower price point.
Because this treatment is somewhat not permanent, consumers need to be disclosed about fracture-filled diamonds when buying. Yehuda, a reputable company based in New York which specializes in clarity-enhanced diamonds has inscribed their name at the girdle of all diamonds they enhanced, which gives sign to gemologist appraisers about the enhancement. However, not all companies do the same. There are many fracture-filled diamonds that have not been disclosed and are sold at the same price as non fracture-filled. There are other tell tails that professionals could detect the fracture-filling treatment in diamonds when looking at them under the microscope such as the flash effect, bubbles in the filler compound, the flow structure of the filler compound, crackled textures, incomplete filling at the surface, cloudy surface or filled areas which are believed to be the result of residue from the treatment process. In some cases, more sophisticated equipment is used to arrive at a conclusion.
As the diamond industry keeps evolving in new technology and invention, we as gemologist appraisers need to keep updating our knowledge and staying alerted in order to do our best in our roles as the witness, identifier and valuer.