How Are Lab-Grown Diamonds Made? CVD vs HPHT Explained
Lab-grown diamonds are made using two main methods: Chemical Vapour Deposition (CVD) and High Pressure High Temperature (HPHT). Both produce genuine diamonds, but they work differently, and understanding the distinction helps you buy better.
What both methods have in common
Whichever process is used, all lab-grown diamonds start with a diamond seed, a tiny sliver of existing diamond crystal. The seed acts as a template, and new diamond material grows on top of it atom by atom until a full gem-sized crystal forms. It takes anywhere from two to twelve weeks depending on the target size and method.
CVD: Chemical Vapour Deposition
CVD is the more common method for gem-quality stones today. The seed is placed inside a sealed vacuum chamber filled with carbon-rich gases, typically methane and hydrogen. The chamber is heated to around 900 to 1,200°C and the gases are energised with microwaves or lasers, breaking them apart and releasing carbon atoms.
Those free carbon atoms rain down onto the seed and bond to it in the crystal structure of the original diamond. Over weeks a crystal grows layer by layer. The result is a flat, squarish crystal that's then cut and polished into a finished gem.
CVD stones often have fewer metallic inclusions than HPHT stones, which makes them popular for high-clarity diamonds.
HPHT: High Pressure High Temperature
HPHT mimics the conditions deep within the earth: extreme heat, around 1,500°C, and extreme pressure, around 1.5 million PSI. A seed is placed in a growth cell with a carbon source, usually graphite, and a metallic catalyst. Heat and pressure dissolve the carbon in the metal, and it crystallises around the seed as diamond.
HPHT was the original laboratory method, developed in the 1950s. It produces crystals of a different shape to CVD, typically octahedral or cuboctahedral. It's also used to improve the colour of some diamonds after growth.
Which method is better?
Neither is definitively superior. Both produce certified, gem-quality diamonds. The differences come down to subtle characteristics that can affect clarity and colour, which is why both are graded individually by laboratories like IGI.
What matters is the specific stone's grade, not the method used to grow it. A well-cut, high-clarity CVD stone and a well-cut, high-clarity HPHT stone are both good choices for an engagement ring.
Explore our lab-grown diamond solitaire rings, each set in solid 18K gold or platinum, with IGI certification on centre stones of one carat and up.
Further reading
- The full science behind lab-grown diamonds
- Are lab-grown diamonds real diamonds?
- Cost comparison: lab-grown vs mined diamonds
See Lab-Grown Diamonds at Una Diamond
Centre stones of one carat and up are IGI certified: