HPHT vs CVD: How Lab Diamonds Are Grown

High pressure, high temperature growth recreates the conditions in which natural diamonds form. A small diamond seed is placed in a press with a carbon source, usually graphite, and a molten metal that helps the carbon dissolve and move. Under enormous pressure and temperatures well above a thousand degrees Celsius, carbon crystallises onto the seed and a diamond grows over days to weeks.

HPHT crystals grow in a blocky, cubo-octahedral form. They can contain tiny metallic inclusions from the growth process, and some are slightly magnetic as a result.

Chemical vapour deposition takes place in a vacuum chamber at low pressure. Thin diamond seed plates sit inside while a carbon-rich gas, usually methane mixed with hydrogen, is energised into a plasma. Carbon atoms separate from the gas and settle onto the seed, building the diamond up in layers over several weeks.

CVD crystals grow as flat, tabular blocks. Many emerge with a brownish tint and are treated after growth to improve their colour. They can show fine dark pinpoints of carbon, and subtle growth layering under specialist equipment.

The differences are mostly invisible once the stone is cut and polished:

No. Both produce real diamond, graded on the same scale. A well-cut, eye-clean stone looks the same whichever way it was grown. Judge the individual diamond by its grades, its report and its appearance, not by the method. If you prefer a stone that has not been treated after growth, look for the as grown note on the report. Our guide to lab-grown treatments explains more.