HPHT Treatment of Diamonds

                                                      ©Suncrest Diamonds. Formerly brown diamonds now pink after HPHT treatment. 

                                                      ©Suncrest Diamonds. Formerly brown diamonds now pink after HPHT treatment. 

The majority of the questions that I have had from clients over the years have been about diamonds. I have received emails, calls, personal appointment all asking the same “How do I buy a diamond, what am I looking for, where can I compromise?”
But, I think the questions that most stick with me are the ones regarding treatments. Most often I get a question like “The salesperson offered me a diamond and then slipped in the word HPHT/clarity enhancement/irradiation/CVD. I didn’t know what that was so I decided to wait.” I generally commended them on waiting, because being informed is the best course a consumer can follow!
Diamond treatments are perhaps the most confusing topic for consumers. Today I want to cover just one HPHT treatment. I am going to break it down by definition, impact on the industry and then what it means to you as the consumer. So without further ado let's dive in!

 ©Suncrest Diamonds The HPHT machine at the Suncrest facility in Provo, Utah

 ©Suncrest Diamonds The HPHT machine at the Suncrest facility in Provo, Utah

What is HPHT treatment?

Type IIa diamonds are the most chemically “pure” diamonds on earth containing few to know impurities. They make up approximately 1-2% of all diamonds and the majority are colorless. However as these diamonds are being pushed towards the surface of the earth they may pick up impurities that color the diamond, the most common color is brown.
HPHT is a permanent treatment used specifically on brown type IIa diamonds subjecting them to enormous amounts of pressure and heat replicating the natural forces that create diamonds. By doing so a near-colorless to colorless color may be achieved, as well as fancy colors such as yellow and green. Furthermore if radiation is combined with the process pink colored diamonds can also be produced.  

                                            © GIA

                                            © GIA


How has this affected the jewelry industry?

HPHT treatment of diamonds first went public in 1999 and it has been a source of anxiety in the gem industry ever since. This trepidation increased after GIA (which has included HPHT testing in their grading since about 2006) released a pivotal statement in 2010 revealing that they had been receiving large numbers of HPHT treated diamonds ranging from 3 to 20 carats in size. The mining industry has also seen a surge in the sales of type IIA brown diamonds with prices steadily escalating as buyers attempt to estimate gains from treatment. The most concerning area has become the increasing number of treated and CVD (lab created diamonds) melee stones (melee is a term to describe small diamonds that range from 0.18 carats down to 0.001 carats) being sold in parcels with natural diamonds. Their small size indicates an increased need for testing of smaller diamonds, as well as the necessity for non-laboratory testing becoming available and affordable for gemologists as an additional line of defense for the consumer. 

© The Practical Gemologist

© The Practical Gemologist


What is the overall opinion of the HPHT treated diamonds and what does this mean for you?

Consumers must be aware that sellers of these stones are required by law to inform them of this treatment as well as any other treatment performed on diamonds (and any other gemstones as well). On the side of the producers of this product they see no difference in the treated and the natural diamond. As mentioned it is a permanent treatment that mimics the natural forces that create a diamond in the earth, however the gemstone and jewelry industry views this quite differently.
Natural stones, those that exist without treatments of any kind have always fetched a higher premium. Why? The simple answer is rarity. HPHT treated stones are considered to null and void the rarity aspect.
There are a few major issues that face the consumer: first generally the price of HPHT treated diamonds is lower than untreated diamonds, however this may differ from dealer to dealer as there is currently little regulation. Second, when it comes to appraising HPHT treated diamonds this must be taken into account. Since the stone is no longer in it’s natural form and we have no way of knowing it’s previous form many appraisers will have to look the the market for comparables to provide an accurate insurance or fair market value. Larger stones 0.75 carat and up)  should be evaluated by a gemological laboratory to confirm that the stone has not been treated. Third, if the consumer is considering a diamond as an investment, or even as an heirloom they must realize that over time a natural untreated diamond will continue to hold and in my personal estimation will gain value over time the same way that natural colored stones have. 

The Take Away:

Overall I do not think that HPHT treatment is inherently bad. In fact in some cases it can make it possible for some consumers to find their dream colored diamond without the higher price tag. To sum up there are just a few simple things to keep in mind:

          © GIA A diamond before and after HPHT treatment. 

          © GIA A diamond before and after HPHT treatment. 

  • HPHT treated stones may not hold their value as well as natural diamonds over time.
  • Disclosure on the part of the seller is required by law. If there's any question you have the right to have the stone examined by a gemological laboratory like GIA.
  • HPHT treated stones frequently have a lesser selling point. This can work to your advantage as a bargaining tool. The savvy consumer could bargain their way to a sizable discount (possibly 20-35%). Think of it kind of like a car dealership and do not be afraid to ask or walk away if it isn’t what you want. (I’ll be writing more on what the guy behind the  counter doesn’t want you to know later!)
  • If you have questions ask an independent gemologist! Independent gemologists have  no ties to a jewelry stores and are not selling gemstones or jewelry. We are here to help advise you and educate you. 

- Kathleen Marino MA, GG (GIA Carlsbad), AJP, NAJA