are effective for identifying characteristic combinations of diamond properties, which help infer diamond type and possibly identify treatments and synthetics. For example, simple observations such as a cross-hatched strain pattern in a colorless diamond that is transparent to short-wave UV radiation indicate that the stone is likely type IIa and should be sent to a laboratory to be tested for HPHT treatment. Similarly, a blue diamond exhibiting electrical conductivity is type IIb and also needs lab testing. If the type IIb blue diamond shows no strain pattern when viewed with cross-polarized light and magnification, then it might be a synthetic. And a strongly colored yellow diamond that does not produce “cape” lines in the spectroscope may be type Ib. If no color zoning characteristic of synthetic origin is present and needles similar to those shown in figure 9B are observed, it is probably a natural type Ib diamond. These are just a few situations where gemological tests can provide clues to diamond type
and its possible implications for identification. Information about type helps gemologists assess the possibility that a diamond is treated or synthetic and, conversely, provides some measure of confidence that it is natural and naturally colored. With the constantly evolving world of treatments and synthetics, however, we strongly encourage gemologists to exercise caution and send their diamonds to a gemological laboratory for testing if there is any doubt.
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