DTC Response To IDEX HPHT Article

We note with interest the article posted on your website (www.idexonline.com) on June 29, 2003 titled ‘Lecture Demonstrates How to Detect HPHT Treated Diamonds’. Educational seminars, such as that given to the diamantaires at the Harry Oppenheimer Diamond Museum in Ramat Gan by Antoinette Matlins-Bonanno, provide useful information on issues such as the identification of colour treated diamonds. 

The article describes the use of a small machine that is used to illuminate white (near-colourless) diamonds with short-wave (ultraviolet) light as a method of determining whether a stone has been high pressure high temperature (HPHT) treated.  We wish to supplement the article by clarifying some of the details.

We believe that the article refers to a device that is used to identify potential rough or polished type II diamonds.   Diamonds are classified as type I or type II depending on their nitrogen content.   Type I diamonds (about 98% of all diamonds) contain measurable nitrogen (evidenced in the infrared part of the spectrum) and, except rare type IaB diamonds, do not transmit short-wave ultraviolet light.   Type II diamonds contain little or no measurable nitrogen and are transparent to short-wave ultraviolet light.  The device is designed to test whether a diamond transmits short wave ultraviolet light and therefore whether it is type II (or in rare cases type IaB).  Such diamonds are those predominantly used in the production of near colourless to colourless HPHT treated diamonds, but there are obviously diamonds of this type that have not been subjected to treatment. We wish to emphasise that this is NOT a positive indication that the stone has been HPHT treated.

Establishing whether a stone has been HPHT treated requires sophisticated photoluminescence measurements involving cooling the diamond to liquid nitrogen temperatures (-196 ÷C) and analysing the emission spectrum of the diamond when excited by specific laser-light.   This method is used by a number of gemmological laboratories, especially those that have a history of fundamental research on the causes of colour in natural and treated diamond.   Indeed, the low temperature photoluminescence method allows the effective detection of the vast majority of HPHT treated colourless, pink and blue diamonds.

Therefore, whilst providing a cost effective method for the identification of type II (or type IaB) diamonds, the device, as reported in the IDEX article, is NOT an HPHT treatment detector. To determine whether the diamond has been HPHT treated requires the services of a suitably equipped and experienced gemmological laboratory.

HPHT treatments are of concern within the trade and have been the subject of a number of recent publications in for example the Gemological Institute of America’s Gems & Gemology  journal and the Rapaport Diamond Report magazine.   In particular we would like to draw the readers’ attention to the review article published last year in Mazal U’Bracha Diamonds, October 2002, Volume 17 no 150, pp 20-40:  Special Focus:  ‘What is the real deal? Diamond Simulants, Synthetics, Treatments and Fillings’.   The review contains a section on the Diamond Trading Company’s (DTC) Gem Defensive Programme (part of its broader Consumer Confidence Programme) titled ‘Gem Defenders On The Front Line’.   It discusses, in particular, the efforts of the DTC Research Centre, UK and its sustained investment in the study of the effects of HPHT treatments on all diamond types and the investigation of criteria that allow the effective detection of HPHT treated diamonds for the benefit of the trade.

Yours Sincerely,

Dr Paul Spear

Senior Research Scientist

For the DTC Consumer Confidence Programme.