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Treated Diamonds. Laser drilling is relatively common in larger diamonds. Laser drilling consists of using a laser to bore a small hole in a diamond. The hole is used to reach a dark inclusion with acid, which bleaches the inclusion to a light color. The laser drill holes themselves can be fracture filled, though this is not always done. The drill hole is so tiny that it is often missed when viewed from the surface of the diamond. Thus, when examining a diamond, it is important to look at the stone in several directions. The laser holes are sometimes quite apparent as long tubes when viewed through the side of the stone (figure 1). But caution is needed because many of the tubes are quite short and only reach slightly below the surface of the diamond. Another way to spot the drill hole is to reflect light off the stone's surface. This will cause the hole to appear as a small black spot on the reflective surface. Running a diamond probe (sharpened steel needle) across the "spot" may enable the viewer to feel the catch of the sharp point in the hole, thus confirming its presence. A new method of laser drilling has been developed recently in which laser pulses are used on an inclusion near a diamond's surface in order to stress the inclusion. This causes the inclusion to fracture the surrounding crystal, resulting in a surface reaching fracture through which the inclusion may be bleached. In the new treatment, the laser drill holes may not reach the surface of the diamond and instead appear as worm-like channels in the stone. Generally, diamonds with low clarity are laser drilled, and even though the inclusions have been bleached to improve their appearance, the inclusions themselves are still present. Stones that appear to have VS or better clarity are not usually candidates for this treatment. However, keep in mind that any diamond can be laser drilled. Though it is considered a permanent treatment, the Federal Trade Commission has reversed its previous decision and made disclosure of this treatment mandatory. Fracture filling Another prevalent diamond treatment is fracture filling. In order for a diamond to be fracture filled, the fractures must reach the surface of the stone. A fracture that is not surface-reaching does not allow the filling material to be introduced into the stone. The filler itself is a glass-type substance, with exact recipes being the proprietary formulas of various companies. Fracture filled diamonds, like laser drilled stones, are usually of lower clarity. Though the fracture is rendered less noticeable by the introduction of the filler, the fracture still exists. In the microscope, using darkfield lighting, the filling material gives a coloured flash--usually blue and orange or purple (figure 2). Practice is needed in order to recognize this "flash effect" and not confuse it with naturally occurring iridescence in some fractures. Other visual clues of fracture filling are the possible appearance of flow structures and trapped gas bubbles in the filler. It is also common for the filler material to be introduced via a laser drill hole. Irradiation This process consists of exposing diamonds to radiation and then to controlled heating. Radiation treatment is seldom detectable using the microscope, as the changes caused are on an atomic level. It often requires major laboratory tests to determine if the diamond has been irradiated. Some diamonds may show microscopic characteristics indicative of radiation, such as a scalloped pattern around the culet or brownish radiation "spots" on the surface, but spectroscopic examination is much more reliable in detecting diamond irradiation. Experience also teaches those of us frequently working with diamonds that certain "overly bright" yellows, greenish blues, and green diamonds are likely to have been irradiated and merit further testing. Natural green diamonds achieve their colour by being exposed to radiation in nature and thus may not be distinguishable from their irradiated counterparts. HPHT (high-pressure high-temperature) HPHT treatment (figure 3) of diamonds is the latest and most controversial treatment on the market. General Electric developed the process in partnership with Lazare Kaplan. It consists of heating specific types of diamonds of lower colour grades in high-pressure environments to raise their colour. These stones are marketed under the brand name Bellataire, and they are laser inscribed in order to identify them as treated. The particulars of the process are proprietary. Recently, fancy colours have been produced using the process. Many
trade periodicals have written about the process and there are reports
of other companies producing these stones without any laser inscriptions.
To date, we feel the most easily recognizable characteristic used
to identify this treatment is the presence of black graphite patches
surrounding inclusions with radiating stress fractures, though this
is tenuous at best. If HPHT is suspected and no laser inscription
is present, it is strongly advised that the stone be sent to a major
gemological laboratory for testing with advanced methods.  
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