GIA receiving HPHT diamonds up to 18 cts.
New York—The Gemological Institute of America (GIA) has noted an uptick in the number of 5- to 10-carat high-pressure, high-temperature (HPHT) treated type IIa diamonds, the lab reported in the latest edition of its Gems & Gemology eBrief.
Authored by Wuyi Wang of GIA Laboratory, New York, the report says the New York lab has examined an increasing number of these larger treated diamonds in recent weeks, with some of the stones weighing more than 10 carats. This included an 18.12-carat diamond that was color graded F. Careful spectroscopic analysis provided confirmed that this big stone was HPHT treated.
The eBrief goes on to state that it is “somewhat unusual” to see larger HPHT-treated diamonds, because HPHT annealing is more likely to damage the diamond and so isn’t typically used on larger stones. It is unclear if this is a new trend or just a few isolated stones, but GIA theorizes that one possible explanation for the larger HPHT-treated diamonds is that more suitable starting materials have become available in the market.