What is a CVD diamond?
A CVD diamond is real diamond grown from gas in a plasma reactor. Here is how it is made, what happens after growth, and what that means for the stones you buy.
How CVD grows diamond
Chemical vapour deposition starts with a seed plate: a thin, flat slice of diamond. Many seeds are placed on a cooled stage inside a vacuum chamber. A mix of mostly hydrogen with a little methane flows in, and microwave energy turns it into a plasma, a glowing ball of hot gas just above the seeds.
In the plasma, methane breaks apart and carbon atoms attach to the seed, continuing its crystal lattice. Hydrogen etches away any carbon that doesn't bond as diamond. The diamond grows upward, layer by layer, for a few weeks. The result is a flat, square-ish block of rough diamond.
After growth: cutting and treatment
The rough is laser-sawn off the seed, planned and cut. Many CVD stones come out of the reactor with a slight brown or grey tint. Growers commonly apply a post-growth HPHT treatment (high pressure and temperature for a short time) to remove it and improve colour.
That is standard practice, but it must be disclosed. A stone sold "as grown" has had no treatment. Ask for the status of every stone, and check that the report agrees.
Colours and sizes
- White: the bulk of CVD production, D to J colour.
- Fancy colours: pink is usually produced by treatment after growth; blue comes from boron added during growth; other colours are possible.
- Sizes: from melee to large single stones well above 10 carats. Larger stones take longer runs and more process control.
CVD vs HPHT growth
HPHT growth crystallises diamond from a metal solvent inside a press, recreating deep-earth conditions. CVD uses low pressure and a plasma instead. Both produce real diamond. CVD is especially strong in larger white stones and Type IIa material; HPHT is strong in small sizes and some colours. A full comparison is in our buyer's guide: CVD vs HPHT.
Questions
Is a CVD diamond a real diamond?
Yes. It is crystalline carbon with the same structure, hardness and optical properties as mined diamond. It must be described as laboratory-grown when sold.
Why are CVD diamonds treated?
Many CVD stones grow with a slight brown or grey tint. A short HPHT treatment after growth removes it. The treatment should be disclosed on the report and invoice.
How long does it take to grow a CVD diamond?
A typical growth run lasts a few weeks. Larger stones need longer runs.