Buyers ask us which is better, CVD or HPHT. It is the wrong question. Both produce real, genuine diamonds with the same physical, chemical and optical properties as mined stones, and grading bodies assess them against identical standards. The right question is which method suits the stone you are trying to buy.
How CVD works
Chemical Vapour Deposition grows diamonds in a controlled plasma chamber. Hydrocarbon gas is introduced at precise temperatures, and carbon atoms deposit layer by layer onto a diamond seed. The result is a real diamond, built atom by atom.
CVD gives precise control over size, colour and clarity. It produces Type IIA diamonds, the purest form of carbon crystal. Most premium colourless lab-grown diamonds in fine jewellery are CVD-grown.
- Grows in a plasma chamber using carbon-rich gas
- Produces flat, tabular rough, which suits rounds and fancy shapes
- Typically Type IIA, the highest purity
- May require post-growth treatment to remove a brown tint
- Preferred for D to F colourless diamonds
How HPHT works
High Pressure High Temperature replicates the conditions deep inside the Earth. Carbon is dissolved in a metallic solvent under extreme pressure and heat, and crystallises around a seed. It produces cubic or cuboctahedral rough, which is better suited to larger stones.
HPHT is also used as a post-growth treatment on CVD diamonds. That is where most of the confusion in the trade comes from: the same three letters describe both a way of growing a diamond and a way of finishing one.
- Replicates the conditions deep inside the Earth
- Produces cubic or cuboctahedral rough, suited to larger stones
- Can grow naturally near-colourless or fancy-coloured diamonds
- Also used to treat off-colour CVD diamonds after growth
What post-growth treatment actually means
Post-growth treatment is any process applied to a lab-grown diamond after it has been grown, to improve its optical properties. For CVD diamonds, the most common is HPHT annealing, which removes residual brown or grey tint by restructuring the crystal lattice and produces a colourless or near-colourless result.
Every treatment we apply is disclosed on the IGI certificate. A buyer should never have to ask.
What this means for your order
For colourless rounds and fancy shapes in the bridal range, CVD is usually the right supply. For large statement stones above 5 carats, and for fancy colours, HPHT growth tends to give better yield and colour retention. In practice we run both, and we match the method to the stone rather than to a preference.
- 1 to 5 carat colourless rounds and fancies: CVD, post-growth treated or as-grown
- 5 to 15 carat statement stones: HPHT and premium CVD
- Above 15 carats: controlled HPHT and advanced CVD growth, produced to order
Ask your supplier which method a parcel was grown with, and ask for the treatment disclosure. If either answer is vague, that is the finding, not the stone.
Mira Gems Supply Desk
Manufacturing and sourcing team, Surat
The people who grow, cut and grade the stones. We write about what we see on the production floor and what buyers ask us in the field.
