History of HPHT
The history of HPHT treatments dates back to 1955, when the General Electric Company first discovered the process for creating diamonds in the laboratory. This led to the creation of HPHT process, whereby GE first created a press where the required pressure and temperature could be maintained for the process. One thing led to another and HPHT treatment evolved through various presses like the tetrahedral, BARS and finally the cubic press. What began as an experiment for diamond color modification in synthetic diamonds has today evolved into usage for natural diamonds also.
Usage of HPHT Diamond Enhancements HPHT treatments basically serve two purposes
- Creation of synthetic diamonds
- Color modification in natural diamonds
Creating synthetic diamonds: To obtain synthetic diamonds, carbon is put inside a grapite capsule. A seed is then inserted into this capsule and a catalyst is added. The diamond grows on the seed while the catalyst enables the crystallization to take place.
Color modification: Different type of diamonds react differently when exposed to HPHT treatments and a range of colors are obtained. For example, diamonds containing aggragated nitrogen, when exposed to HPHT can cause it to become single substitution nitrogen. In such cases, diamonds having green, orange and yellow hues can be created. In diamonds where nitrogen is negligible, the process is often used to produce colorless diamonds. Thus brownish diamonds when HPHT processed can obtain a colorless hue. A light pink color may also be obtained in some cases. In case of diamonds with negligible nitrogen and presence of boron, HPHT can alter the color. Thus brownish diamonds will lose the brown tone and boron will make the stone bluish in color.
Popular presses used for treatment
Belt presses: This was the initial form of press used for treatment. Here pressure is created by the usage of two high strength pistons that provide equal pressure in opposing directions on a sample. A series of rings surround the sample in order to contain the pressure.
Torid press: In this method, the two pistons apply pressure in a single vertical direction.
Cubic press: This uses many pistons that provide pressure from different directions. It is also known as a tetrahedral press.
Procedure of HPHT
If a customer intends to give diamonds for this treatment, the following procedure is used,
- The stone is first inspected by diamond experts for cracks, fractures etc. Stones are also subject to chemical analysis using scientific equipment. Once it is confirmed that the treatment can be undertaken, the same is informed to the customer.
- Depending upon the properties of the stone, the color that may be obtained after treatment is deciphered and the customer is informed about the same.
- Pressure of over 1,000,000psi is applied by placing the stone in an internal pressure medium that distributes the pressure on the entire diamond equally.
- The internal pressure medium is placed into a heat generating sleeve where temperatures start at 1800 degrees centigrade.
Pricing of treatments: Cost for these treatments varies with the size of the diamond. Also the total number of stones given and additional services like repolishing are charged extra. While these treatments are expensive,
Organizations and HPHT
Because HPHT is controversial, different bodies follow different guidelines for HPHT. As per the Federal Trade commission, HPHT treated diamonds must be disclosed to the user. General Electric follows this norm and all diamonds that are HPHT treated are laser inscribed with the terms ‘HPHT PROCESSED’, IRRADIATED. If GIA notes diamonds to be HPHT treated, it also specifies them as ‘HPHT ANNEALED’ or ‘Artificially Irradiated’. Such details are displayed prominently on the grading report under ‘origin’ in the ‘color’ section of the report.
Pros and cons
The HPHT treatment of diamonds is a controversial issue because it has both advantages and disadvantages. These are further discussed as under.
- The treatment is permanent and diamonds are stable in the normal conditions of wear and care.
- It can dramatically alter the color of brownish diamonds to make it more appealing. Light brown color diamonds can be rendered almost colorless using this process.
- The process causes surface graphitization and the diamond needs to be polished to remove it.
- It is difficult to differentiate between regular natural diamonds and HPHT treated diamonds.
- It can cause marginal weight loss in a diamond.
- It can reduce the clarity of the stone.
As HPHT has become more commercially available, today there are various methods available to detect if your stone has been HPHT processed or not. At the basic level diamonds over 0.5 carat can only be HPHT treated. A trained gemologist may use equipment like the SSEF spotter and crossed polarization filter to detect the same. DiamondSure is also used to separate cape diamonds from the rest. At the next level FTIR and UVVIS spectroscopes are used and synthetic and PT treated diamonds can easily be identified ere. Besides this, renowned laboratories have many other proprietary procedures that they use to identify such diamonds.
With all sophisticated equipment it continues to be difficult to detect HPHT processed diamonds at many instances. It is thus important that you purchase diamonds from a trusted vendor online or offline. Diamonds accompanied with a certificate from a reputed laboratory like GIA also ensure that diamonds are completely natural. You could also choose signature or top of the line branded diamonds to protect yourself. Finally, if you cannot afford GIA stones, make sure to opt for a diamond that is accompanied by a certificate from a renowned laboratory.