Updated terminology for HPHT-treated sapphires

Meggen, 7 September 2018

GRS has decided to update the treatment disclosure terminology used for sapphires enhanced by heat at elevated pressure (published in the literature as HPHT, Song, J. et al. 2015)

Generally the pressure applied to diamonds during the diamond HPHT treatment process is much higher than that of the sapphire treatment. GRS has thus changed its treatment code for sapphires heated at elevated pressure from HPHT to PHT (“Pressure, High Temperature”). In the comment section of the GRS report it will be mentioned as follows:

Comment: PHT (also referred to as HPHT, see reverse side for details).
The reverse side defines HPHT as heated at elevated pressures.

NEW: New comment ‘PHT’ used for sapphires enhanced by heat at elevated pressure

OLD: Previous comment ‘HPHT’ used for sapphires enhanced by heat at elevated pressure

Comment ‘H” used for sapphires enhanced by conventional heat treatment


Song, J. Noh, Y., and Song, O., 2015,. Color enhancement of natural sapphires by high pressure high-temperature process, Journal of the Korean Ceramic Society, Vol.52, No. 2, pp.165-170

Choi H., Kim S., Kim Y., Leelawatanasuk T., Lhuaumporn T., Atsawatanapirom N., Ounorn P., 2018. Sri Lankan Sapphire Enhanced by Heat with Pressure. The Journal of The Gemmological Association of Hong Kong, 2018 Volume XXXIX, 16-25.

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