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1 Gemological Institute of America, Research Department, 5345 Armada Drive,
Carlsbad, CA 92008-4603, USA
E-mail:
jshigley{at}gia.edu
Annealing of gem-quality diamonds at very high pressures (above 5 GPa)
and temperatures (above 
1800°C) can produce significant changes in
their color. Treatment under these high-pressure-high-temperature (HPHT)
conditions affects certain optically active defects and their absorptions in
the visible spectrum. In the jewelry industry, laboratory-treated diamonds are
valued much less than those of natural color. Polished diamonds are carefully
examined at gemological laboratories to determine the "origin of
color" as part of an overall assessment of their quality. Currently, the
recognition of HPHT-treated diamonds involves the determination of various
visual properties (such as color and features seen under magnification), as
well as characterization by several spectroscopic techniques. HPHT-treated
diamonds were introduced into the jewelry trade in the late 1990s, and despite
progress in their recognition, their identification remains a challenge. While
some detection methodologies have been established, the large number of
diamonds requiring testing with sophisticated analytical instrumentation poses
a logistical problem for gemological laboratories.
KEYWORDS: diamond, gemstone, color, treatment, HPHT, annealing, identification
This article has been cited by other articles:
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  J. E. Shigley and S. F. McClure Laboratory-Treated Gemstones Elements, June 1, 2009; 5(3): 175 - 178. [Abstract] [Full Text] [PDF]
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