How are synthetic diamonds grown?
From a tiny diamond seed to a finished gemstone.
Synthetic diamonds don’t simply appear fully formed in a laboratory. Their growth begins with a small diamond seed or substrate, which provides the crystal structure upon which new diamond material can grow. Today, there are two principal methods used to create synthetic diamonds for jewellery: HPHT (High Pressure, High Temperature) and CVD (Chemical Vapour Deposition).
Both can produce diamond, but the way the crystal grows is very different.
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HPHT: High Pressure. High Temperature.
HPHT was the first method to successfully produce gem-quality synthetic diamonds. It recreates some of the extreme conditions associated with natural diamond formation, but does so inside a highly controlled growth chamber.
A small diamond seed is placed inside a capsule with a source of carbon, typically graphite and a metallic material that acts as a flux.
The chamber is subjected to extraordinary pressure and temperatures of approximately 1,300–1,600°C. The carbon dissolves within the molten metal and moves towards the cooler diamond seed, where carbon crystallises onto it and the diamond gradually grows.
CVD: Chemical Vapour Deposition.
Diamonds, grown layer by layer. CVD, Chemical Vapour Deposition takes a very different approach.
Thin diamond seed plates are placed inside a vacuum chamber containing hydrogen and a carbon-containing gas, typically methane. Energy, commonly microwaves, is used to activate the gases and create a plasma. The process releases carbon-containing species which reach the diamond seed. Carbon is incorporated into its crystal structure and, over time, diamond material builds up in thin layers across the seed.
