Friday, March 29, 2024
spot_img

Sapphires treated combining high pressure and high temperature. Which disclosure policy to follow?

Sapphires are at the centre of one of the most controversial gemological issue arisen in between 2018 and 2019. This issue is related to heat treatment enhanced by pressure which reportedly got under way in Korea some years ago. The company which developed this treatment did not provide technical details on the producing method, but there are indications confirming that the technique is similar to the one used for diamonds though different in procedure. It is also known that the original materials used by implementing this technique are mostly pale blue sapphires from Sri Lanka and that for the enhancement process, there was no addition of any chemical element. Many people involved in the trade in that country reported an unexpected increase of price of rough sapphires previously considered not suitable for a successful traditional heating treatment.

In 2015 these new type of heated sapphires more consistently appeared in the market giving rise to some uncertainty, thus forcing all the major international labs to work on their identification. So it was necessary to decide how to account for these sapphires. In the same year GRS decided to separate the disclosure of what they renamed PHT sapphires (Pressure High Temperature Treatment) from conventional heat treated sapphires. The last explanatory Update of GRS was published in January 2019.

Sapphires heated with a new heating process, incorrectly named High Pressure-High Temperature (HPHT) heating in the trade. (Photo: LMHC Press Release)

In 2016 GIT released an Update on the matter which revealed that “those sapphires showed the presence of a unique strong absorption band centered around 3040-3050 cm-1 on the IR spectrum”. This is why this Thai Gemological Institute decided to point out in its reports’ comments: “Gemological evidences suggest enhancement by High Pressure High Temperature process”, each time the assumed diagnostic broad absorption bands should be detected. Also AGTA, the American Gem Trade Association, decided in December 2018 to declare the combined pressure/heat sapphire treatment in a distinctive way.

But this policy was not followed by LMHC (a Harmonization Committee grouping together important Labs such as CGL, CISGEM, DSEF, GIA, GIT, Gübelin Gem Lab and SSEF) which in its November 2018 press release stated that the new sapphire heat treatment is “incorrectly named High Pressure-High Temperature (HPHT) […] Current scientific knowledge and available data from the LMHC laboratories indicate that the […] treatment is essentially a form of heating, and as such is similar to most known heating techniques. It consequently does not currently require specific reference on the laboratory reports of the LMHC members”. At the moment these different points of view are feeding a lively debate among many traders and gemologists also in the Social Media. The topics under discussions, beyond the question of whether or not to disclose this treatment, and how, are focused on microscope investigation aimed at detecting revealing features. This is a crucial point for small labs lacking spectrophotometric equipment.

For further reference some sources on the issue are listed below:

Gem News published on IGR – Italian Gemological Review #6 – Spring 2019

Articoli correlati

LASCIA UN COMMENTO

Per favore inserisci il tuo commento!
Per favore inserisci il tuo nome qui

spot_img
spot_img
spot_img
spot_img
spot_img
spot_img

NEWS

spot_img
spot_img
spot_img
spot_img
spot_img
spot_img

Dal Magazine