HPHT is one of the well-known methods to make diamonds in the lab. However, there are two types of high-pressure high-temperature processes, HPHT treatment and HPHT diamond growth. The latter as mentioned deals with growing the diamond in the lab and the former involves altering the colour of natural diamonds.
Let's look at both processes in detail:
HPHT diamond growth
Unlike diamond stimulates like moissanite and white sapphire, HPHT diamonds consist of the same chemical and physical properties as naturally grown diamonds.
This process subjects carbon to extreme temperatures and pressures meant to replicate the conditions within the earth during the diamond creation process.
The diamond seed is placed in a small capsule within an apparatus that generates high pressures similar to those found within the earth. The capsule consists of a carbon starting material that dissolves in a molten flux consisting of metals which lower the temperature and pressure to the required amount.
The image was taken from the GIA source
Then during the processes the carbon material moves through the flux and towards the diamond seed and crystallizes to create a synthetic diamond crystal, this process takes up to a couple of weeks.
The substance is then cooled to form a diamond after which it is cut and polished like a naturally grown diamond.
The image was taken from the GIA source
The growth pattern of a natural diamond is crystals formed as octahedrons whereas, in the HPHT method, the crystals are formed with additional cubic faces. Due to this, the growth patterns are different and this is one of the ways to determine their difference.
There are two methods to grow diamonds in the lab: HPHT and CVD. HPHT diamonds tend to be of a higher quality than CVD diamonds and it is easier to control the conditions during the development process.
Read more about these two types of processes and the inclusions developed here: https://www.linkedin.com/pulse/inclusions-natural-lab-diamonds-glaze-diamonds
HPHT colour treatment
HPHT treatment to change the colour of natural diamonds was discovered as a byproduct of annealing natural diamond anvils. The same machines, like a hydraulic press that produces extremely high pressure and temperature environments, are also used to treat both mined and laboratory-grown diamonds.
This process is said to bring a diamond into its "fully matured" state. The process involves the diamond being placed in a containment cube surrounded by heating mechanisms. The cube is then treated to the same amount of pressure that the earth creates when forming diamonds which brings the diamonds into a mature, desirable state.
The image was taken from the GIA source
Natural white diamonds have impurities in them shown as hints of yellow or brown, this affects their colour grade. HPHT treatment can change the colour of diamonds or make them colourless and therefore enhance the diamond to desirable colour grades.
The image was taken from the GIA source
For example, a natural 5.20 ct type Ia SI2 Fancy Dark yellowish brown diamond with natural anhedral crystal inclusions after being treated was resubmitted as a 5.17 ct type Ia SI2 Fancy Deep yellow-orange diamond.
While there are many different treatments that can be performed on diamonds, HPHT treatments are permanent and require a stable and controlled environment.
Most diamonds can undergo this process except diamonds with low clarity grades that might break apart during the process. Diamonds of clarity grade VS2 and above are eligible for this treatment, if there are slight inclusions in the stone it can blow up during the process.
As technology advances, HPHT treatments are becoming more common for both natural and laboratory-grown diamonds.
How to tell if a diamond has been HPHT Treated?
An average person would not be able to tell the difference between an HPHT diamond and a natural diamond. One must always rely on expert gemmologists who will consult the diamond certification and the diamond characteristics.
We provided diamond evaluation and grading services and help you verify your diamond. With our GIA-certified diamond experts, we will provide you with options to ensure you receive the best return on investment for your price.
Book a consultation with us: https://www.glaze-diamonds.com/contact
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