March 2, 2000
GIA Studies Colored GE/POL Diamonds
The Gemological Institute of America has released a study of GE/POL yellowish green diamonds that have been processed through high pressure/high temperature conditions. The study confirms the colors are achieved without irradiation.
The study is a collaboration between General Electric and GIA researchers. The greenish diamonds are to be marketed by Pegasus Overseas Ltd., a subsidiary of Lazare Kaplan International, New York City.
The report says GE first developed the HPHT technology to produce yellowish green diamonds in the mid-1990s, using Type Ia diamonds, and that GE had decided at that time not to make a commercial venture of their findings.
Natural diamonds with some similar characteristics to the GE/POL diamonds are said to be found in limited quantities in localities such as Sierra Leone, Ivory Coast and Brazil.
Among the findings discussed are the chameleon-like characteristics of the diamonds. Upon heating to 550-650° Celsius, the GE/POL diamonds' color changes from a yellowish green to a pure "emerald" green. The color reverts to its original yellowish green color upon cooling to room temperature. In natural (untreated) chameleon diamonds, the change happens in the reverse order initially grayish green, the diamonds change to yellow upon heating.
Among the identifying characteristics noted:
The greenish yellow diamonds are to be sold with laser inscriptions on the girdle facets. GE/POL is evaluating consumer demand for yellowish green diamonds and is also evaluating designer jewelry specifically designed for the stones.
The report also underscores the trade's need to recognize that new technology is being developed by GE and other entities that will make more diamonds like these available in the future.
- Colors: The colors range from greenish yellow to yellow-green which, because of luminescence, exhibit a stronger green color in daylight or a strong incandescent light source.
- Luminescence /Fluorescence: The diamonds show strong greenish yellow fluorescence to long-wave ultraviolet radiation, and a weaker reaction to short-wave radiation. The stones show weak-to-no phosphorescence.
- Clarity and Internal Features: The GE/POL diamonds have a broad range of clarity grades and most diamonds studied had well-defined color zoning that luminesced a bright green color under strong fiber-optic illumination.
- Spectra: The diamonds showed several spectroscopic lines that are consistent with the colors and optical centers for the type of diamond studied. Researchers also noted a few lines of "unidentified cause."
- by Robert Weldon, G.G.