What do HPHT and CVD diamond mean? And which is a better option? As you dive deeper into your research of lab grown diamonds, you start to realize that there are more similarities than differences between lab grown diamonds and their natural counterparts. Apart from how they’re actually made (think of an IVF baby in comparison to a naturally conceived one), everything else from how it looks to the grading certification is pretty much the same!
There are currently 2 distinct methods of creating a lab grown diamond—HPHT & CVD. You’ll be surprised to hear that we do not often get asked what the differences are, but since you are reading this, I am sure you’re now curious if one is better than the other, and which should you go for.
HPHT was the first ever method of creating lab grown diamonds. The first reported lab grown diamond was invented by Tracy Hall, a General Electric chemist back in 1954; there are rumours of earlier successful attempts but none of which have been confirmed. HPHT involves placing a diamond seed within a chamber with graphite under extreme temperature and pressure to form a diamond rough, mimicking how diamonds are naturally made on the earth. Temperatures in the chamber can exceed 1500˚C with pressures of about 1.5 million pounds per square inch!
CVD is the more modern process involving a diamond seed exposed to hydrocarbon gases which are ionised, allowing the carbon to be deposited on the seed, forming the diamond rough. This process mimics how diamonds are formed in interstellar gas clouds - that’s right, space diamonds! The CVD process is not limited to just making diamonds, but also for many other commercially important materials such as silicon compounds and metals.
Now that you know what both of the 2 methods are, which process creates The Better Diamond? Despite the differences in techniques used to grow these diamonds, each method has its own practical purpose and should not be regarded as better or worse. For example, lab grown diamonds under 1 carat are often grown via HPHT due to cost effectiveness. It is notable that HPHT diamonds sometimes do not pass the diamond hardness test and falls just short of a 10 on Mohs scale of hardness. But for all intents and purposes, it is still a diamond.
CVD diamonds on the other hand tend to produce diamonds of poorer colour and clarity. They are then required to undergo a HPHT process to improve their grade, which is why you’ll notice that the IGI certificate of a CVD diamond often states “This Laboratory Grown Diamond was created by Chemical Vapor Deposition (CVD) growth process and may include post-growth treatment”, whereas a HPHT diamond will be “As Grown - No indication of post-growth treatment This Laboratory Grown Diamond was created by High Pressure High Temperature (HPHT) growth process”.
Another difference is that HPHT creates Type II diamonds whereas CVD creates Type IIa diamonds. A Type II diamond simply means that a diamond has little nitrogen impurities whereas a Type IIa diamond is as pure as a diamond can get with almost no impurities of any sort. In the world of natural diamonds, Type IIa are the rarest (forming less than 2% of diamonds found) and most collectable diamonds, which is probably why we sometimes get requests from clients to specifically select a CVD diamond for them. However, when it comes to lab-grown diamonds, a Type IIa diamond then becomes nothing rare or unusual as it is simply the by-product of a CVD grown diamond.
The morphology of a HPHT and CVD diamond also differs but does not reflect a difference in physical appearance. At the end of the day, both methods are able to yield diamonds of colour and clarity grades across the spectrum, and are certainly not discernible from each other, nor from natural diamonds, to the naked eye. As with most meaningful discussions in life, it is important to look at diamonds on a case by case basis and not to make sweeping generalisations based on the 2 methods. If in doubt, feel free to reach out to any one of our friendly consultants who will happily guide you through the process of picking The Better Diamond.