CVD vs HPHT: How Are Lab-Grown Diamonds Made?

Lab-grown diamonds are made in two ways: with the CVD method or with the HPHT method. Customers ask about it more and more, and certificates sometimes state the growth method. In this article we explain how both work and what the difference means for the stone.

1. How does a diamond form?

A diamond is carbon that crystallises under special conditions. In nature this happens deep in the earth, under enormous pressure and heat, over millions of years. In a laboratory those conditions are recreated or reached in another way, so that a diamond grows in a few weeks.

In both cases the result is a diamond, with the same chemical composition, crystal structure and hardness.

2. HPHT: high pressure, high temperature

HPHT stands for High Pressure, High Temperature. This method recreates the conditions inside the earth.

• A small diamond seed is placed in a press, together with carbon and a metal solvent.
• The press builds up a pressure of more than 50,000 times atmospheric pressure, at temperatures around 1,300 to 1,600 °C.
• The carbon dissolves in the metal and crystallises layer by layer on the seed.

HPHT diamonds typically grow in a cuboctahedral shape. They can sometimes contain small metallic inclusions, a remnant of the solvent.

3. CVD: chemical vapour deposition

CVD stands for Chemical Vapor Deposition. Here the diamond is built up, as it were, atom by atom.

• Thin diamond plates serve as seeds and are placed in a vacuum chamber.
• The chamber is filled with a gas mixture of methane and hydrogen.
• Microwaves create a plasma that releases the carbon from the gas.
• The carbon is deposited layer by layer on the plates.

CVD diamonds grow in flat, tabular blocks. After growth they often receive a short HPHT post-treatment to improve their colour. This is common practice and is stated on the certificate.

4. CVD and HPHT side by side

5. Which method is better?

Neither is better by definition. Both methods produce excellent stones, and both also produce average ones. The quality of an individual stone is determined by the 4 Cs: carat, cut, colour and clarity.

Advice for jewellers: look at the certificate and the stone itself, not at the growth method. For the customer, the method is mainly an interesting story.

6. How do you identify a lab-grown diamond?

With the naked eye and a loupe, the difference from a natural diamond cannot be seen. Laboratories such as IGI and GIA use spectroscopy and fluorescence imaging to recognise the growth patterns of CVD and HPHT. Read more about certificates in IGI or GIA: how to read a certificate.

Frequently asked questions

How long does it take to make a lab-grown diamond?

Depending on size and method, a few weeks. The rough stone is then cut and polished, just like a natural diamond.

Is a CVD diamond a diamond?

Yes. A CVD diamond is chemically and physically a diamond, just like an HPHT diamond. It is not an imitation.

Is the growth method stated on the certificate?

Often, yes. An IGI certificate states the growth method and any post-growth treatments.

Top-quality lab-grown jewellery

Noam Jewels selects lab-grown stones from the Antwerp diamond district and sets them in more than 1,500 designs in 14k and 18k gold. Create your B2B account or book a call.