Understanding HPHT Diamond Treatments

Understanding HPHT Diamond Treatments

The future of the diamond markets will include diamond treatments

If there is one thing that is certain about the future of the diamond business, it’s that we are going to have to embrace and accept diamond treatments. Without them, a huge market supply of lower quality (read: lower cost) diamonds would be unsaleable. Why allow so many lower color but potentially viable diamonds to go unsold when a couple of basic treatments can turn them into totally viable diamonds? We say….bring on the treatments! All we need is for the markets to get a better understanding of HPHT diamond treatments.


Type I diamonds have clumps of nitrogen interspersed within the crystal lattice. By applying high pressure and high temperature to the diamond, this nitrogen is dispersed throughout the diamond making the color much more acceptable, quite often becoming a light fancy greenish yellow as seen at left. As you can see from the cloudiness of the color, the Type I HPHT diamond will sometimes have a very strong reaction to ultraviolet with a strong yellow/green reaction common. While the lesser quality Type I diamonds are known to produce this result, in the best cases these diamonds turn a vivid fancy yellow as with the Bellataire™ pear cut diamond seen below from the ISG Student Reference Collection.

The treatment is actually pretty simple, particularly when one can see what we like to call our “Cheezy Graphics”, that description is what we use to denote some of the quick and easy graphic demonstrations we use to explain some otherwise complicated issues. Here is our Type I HPHT Cheezy Graphic below left which better explains how the Type I HPHT works using high temperature and high pressure to disperse the nitrogen in the diamond crystal shape. Below right is an amazing fancy yellow Type I HPHT from Bellataire that is beautiful….and affordable!



In the case of Type II diamonds, there is no nitrogen in the crystal (by definition) but the inferior color is due to deformations in the crystal lattice. This deformation of the crystal structure causes the diamond to transmit an undesirable color which can be corrected by subjecting the diamond to high temperature and high pressure. This HPHT process takes the diamond almost to the melting point at which the diamond itself reforms, or “heals,” the deformation of the crystal lattice. In other words, the high temperature and high pressure takes the diamond almost back to the point of the original formation that went wrong and allows it to reform correctly. In the case of the Type II diamonds the crystal becomes basically colorless, losing the unwanted color created by the deformation in the original crystal lattice.Once again, a simple graphic demonstration of the process showing the concept. Below right is another Bellataire diamond, this one of Type II and again a part of the ISG Student Reference Collection.


Identification of HPHT Treated Diamonds

Type I HPHT treated diamonds are generally well known for their strong greenish/yellow fluorescence. The strength of this reaction is a major “tell” that the diamond has been HPHT treated, but we note a word of caution that this is not always a diagnostic feature. Below is a photo of the Type I HPHT diamond at the top of the page showing in ambient light and UV.

HPHT diamonds have been made much less of a problem to identify, thanks to the work of Wolf Kuehn and the folks at the Canadian Institute of Gemmology with their new GL Gem Raman. This amazing technology can easily identify HPHT treated diamonds, and the GL Gem Raman is the best on the market. It is also the most affordable…well within reach of any professional gemological lab or appraiser. Examples of a Raman scan of a natural diamond (below left) and from our Bellataire™ HPHT treated diamond (below right) . As you can see, the separation of the HPHT is quite graphic and should take the fear out of these important diamonds for future marketing.

Anyone who plans on being in this business for a while needs to start thinking in terms of created and treated gemstones if you are planning on being profitable. The mines cannot keep up with demand if that demand is only for natural, untreated gemstones. We must broaden the market acceptance of the treatments in order to utilize more of the production from each mine. Its a matter of knowledge, a matter of training, and in the case of certain types of diamonds…its a matter of getting a better understanding of HPHT treatments and the benefits they offer to everyone in the diamond market.

Robert James FGA, GG