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CVD and HPHT: two routes to the same crystal.

Every laboratory-grown diamond starts with a real diamond seed. The growth method determines the conditions under which carbon attaches to that seed — and, to a degree, the kind of inclusions the finished stone carries. Neither method makes a diamond more or less of a diamond.

Diagram of a diamond seed, growth chamber and finished faceted diamond

Method one

Chemical Vapor Deposition

A thin, polished diamond seed plate is placed in a vacuum chamber. Hydrogen and a carbon-bearing gas such as methane are introduced, and microwave energy ionises the mixture into a plasma. Carbon atoms release from the gas and settle onto the seed, continuing its lattice one atomic layer at a time while the hydrogen etches away any non-diamond carbon that tries to form alongside it.

Growth runs for weeks and is often paused so the plate can be cleaned and restarted. Because the crystal grows upward as a slab, cutters get efficient yield on elongated shapes. Many CVD crystals are annealed afterwards — heated under controlled conditions — to clear a faint brown cast that can develop as grown.

Method two

High Pressure / High Temperature

A seed sits at the cool end of a growth cell packed with a carbon source and a metal flux. A press brings the cell to roughly five gigapascals and around 1,400 °C. The carbon dissolves into the molten flux, migrates toward the seed, and recrystallises onto it as a single diamond crystal — the same dissolve-and-deposit mechanism that operates in the earth, compressed into weeks.

HPHT rough grows outward in a blocky habit that suits rounds and cushions. Its signature inclusion is a trace of the metal flux, which is why some HPHT stones respond faintly to a strong magnet — a curiosity, not a defect, and one of the clues a laboratory uses to identify origin.

Side by side

 CVDHPHT
ConditionsRoughly 700–1,200 °C in a low-pressure plasma of hydrogen and methane.Roughly 1,300–1,600 °C at about 5–6 GPa, close to mantle conditions.
Growth directionLayer by layer on a flat seed plate, producing tabular rough.Outward from a seed in a metal flux, producing cuboctahedral rough.
Typical growth timeTwo to four weeks for a gem-sized crystal.Days to a few weeks depending on target size.
Characteristic traitsFine striations, occasional pinpoints, sometimes brown-tinted as grown.Metallic flux inclusions; can be faintly magnetic; occasional blue nuance.
Common post-growth stepFrequently annealed to remove residual color.Often grown to final color without annealing.
Shapes it favorsElongated shapes — ovals, emeralds, radiants — cut efficiently from tabular rough.Rounds and cushions cut efficiently from blocky rough.

Questions we actually get

Is one method better than the other?
No. Both produce diamonds that grade across the full color and clarity range. A superb CVD stone will outperform a mediocre HPHT stone and vice versa. The grading report, not the growth method, tells you what you are buying.
Does post-growth treatment make it 'less real'?
Annealing is a heat process applied to the diamond itself; the material remains diamond throughout. It is disclosed on the grading report where applicable, and we list any treatment on the product page. What we never sell is a coated or fracture-filled stone.
Should I ask which method my stone used?
You can, and we will tell you. In practice, buy the stone in front of you: cut quality, whether it is eye-clean, and how it looks in your metal will affect your daily experience of the ring far more than the reactor it came out of.
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