Lab Grown Diamonds: HPHT vs. CVD Explained

HPHT and CVT diamonds: is one better than the other?

The answer isn’t too complicated, but requires a bit of explanation. Lab grown diamonds are made in laboratories using one of two methods. The first method involves replicating the high pressure and high temperature (HPHT) found in the earth’s mantle where mined diamonds are formed. The second method is known as CVD (or Chemical Vapor Deposition) and this is where superheated gas is used to stimulate and grow a small ‘seed’ of diamond crystal into a full sized diamond. 

At Taylor & Hart, we provide both types of lab grown diamond but it’s important to note that any CVD diamond we offer has also undergone the HPHT process after its production. HPHT is a great way to enhance any diamond’s clarity and colour (sometimes natural diamonds undergo this process as well!) and we find that CVD diamonds that have been finished in this way look better and brighter than gemstones that have undergone CVD alone.

Are lab grown diamonds real diamonds?

Yes! Sometimes a lab grown diamond is described as a ‘synthetic diamond’. However this terminology is somewhat misleading as lab grown diamonds have an identical chemical and physical structure as mined diamonds, and as such should only be distinguished by the means of their production.

This is especially true in comparison to other crystals such as cubic zirconia or moissanite which are well known diamond simulants or diamond alternatives. These crystals have a completely different chemical structure to lab grown diamonds and should only be seen as a diamond substitute.

Lab grown diamonds vs. earth mined diamonds

Compared to a natural diamond, a laboratory grown diamond is optically, physically, and chemically the same as an earth mined diamond. Lab grown diamonds, whether grown in with the HPHT or CVD method, have some key advantages compared to mined diamonds. Because of the high cost of mining and rarity of an earth grown diamond, man made diamonds are almost 40% cheaper than a natural diamond. Lab grown diamonds also come from a transparent supply chain and can be more ecologically sustainable, especially if grown with renewable energy sources.

Rose gold rope band with cushion cut diamond

HPHT Lab Grown Diamonds

What are HPHT lab grown diamonds?

The process to create an HPHT diamond (High Pressure High Temperature) was initially developed in the 1950s for industrial purposes. As mentioned above, the HPHT process can also be used to treat mined diamonds to enhance their overall colour and clarity. The process was designed to mimic the pressure and temperatures found within the earth where natural diamond crystals are formed over millions of years. The HPHT process manages to recreate this environment, but allows a diamond to form in a matter of weeks compared to the roughly 150 million years it took to form the world’s natural diamonds!

How are HPHT diamonds made?

Mined diamonds in the earth are created miles underneath the earth’s surface under extremely high pressure and scorching temperatures of over 2000 degrees celsius. An HPHT diamond (High Pressure High Temperature) needs to be created in roughly the same conditions. There are three basic manufacturing processes to create HPHT diamonds: the belt press, the cubic press, and the split beer (BARS) press. With each process the presses create an environment of high pressure and temperature into which a small diamond encased in carbon is left for many days until its formed a full sized diamond.

A company called General Electric created the first lab grown diamond, which was brown and heavily included. The diamond was cut for industrial uses to create tools for cutting, grinding and drilling. Over time, the process became refined enough to be used for jewellery.

What are the benefits of HPHT diamonds?

There are some small differences between a HPHT vs CVD diamond, but as a jeweller we only procure diamonds that meet our quality standards. Because of this, you’ll only find diamonds with high quality colour and clarity in our lab grown diamonds search tool, regardless of how they were produced. But we do like to let our customers know that any CVD diamonds we offer will have also undergone an HPHT treatment in order to give them the best finish possible.

CVD Lab Grown Diamonds

What are CVD diamonds?

A CVD diamond (Chemical Vapour Deposition) is a recently invented technique in which diamonds are grown from a hydrocarbon gas mixture, similar to how diamonds form in interstellar gas clouds. The CVD process was created in the 1980s and is generally understood to be the less costly method of creating diamonds out of the two as it requires much less energy.

How are CVD diamonds made?

A thin slice of diamond seed is placed in a sealed chamber and heated to around 800 degrees celsius, and then the chamber is filled with other carbon rich gases such as methane. The gases are ionised into plasma using microwaves, lasers, and other techniques. The ionisation breaks down the gases and allows the carbon to merge with the diamond seed, growing the diamond up layer by layer.

What are the benefits of CVD diamonds?

Generally, the CVD process produces lab grown diamonds of a high clarity. The CVD process can produce colourless diamonds easily because the process doesn’t involve metal. The CVD process is also less energy intensive, producing more competitively priced diamonds. 

HPHT vs CVD diamonds

Ultimately, the key difference between an HPHT diamond and a CVD diamond is that they have different diamond growth patterns. If inspected closely with magnification, a lab diamond expert would potentially be able to tell the difference between an HPHT and a CVD diamond by looking at the crystal structure. HPHT diamonds grow in a cuboctahedron shape and have 14 different growth directions, while a CVD diamond has a cubic shape and only one growth direction. This can sometimes cause a CVD diamond to show evidence of strains, but this is rare and only can be seen under magnification.

Historically HPHT diamonds have produced higher amounts of colour, but with advances in technology both methods can now produce colourless diamonds.

Which type of lab grown diamond should I purchase?

At Taylor & Hart, we sell both HPHT and CVD diamonds. We feel that both methods can produce high quality diamonds, therefore we don’t choose one over the other when procuring our lab grown diamonds. When you’re shopping for a lab grown diamond with us, it’s important to note that while all of our lab grown diamonds are IGI (International Gemological Institute) certified, the method of growth isn’t always stated. All of our diamonds are inspected for quality control and have an excellent cut, clarity and colour. No matter which method, a lab grown diamond that has excellent characteristics will stand the test of time. 

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