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The Science Behind Lab-Grown Diamonds: CVD and HPHT Explained

The Science Behind Lab-Grown Diamonds: CVD and HPHT Explained

Lab-grown diamonds aren't imitation diamonds. They're not cubic zirconia. They're not moissanite. They're real diamonds, carbon atoms in the crystal structure that defines a diamond, created in a laboratory rather than extracted from the ground. Here's how they're made.

Two methods, one result

There are two ways to grow a diamond in a lab: HPHT (High Pressure High Temperature) and CVD (Chemical Vapour Deposition). Both produce genuine diamonds. The method affects some aspects of the process, but not the quality of the finished stone. That's determined by the conditions maintained during growth and the skill of the cutter afterward.

HPHT: replicating the earth's mantle

The HPHT method mimics what happens deep underground. A small diamond seed is placed in a press along with carbon and a metal catalyst. The press applies extreme heat (around 1,400°C) and pressure (around 60,000 atmospheres). Under these conditions the carbon melts and begins crystallising around the seed, growing the diamond layer by layer over days or weeks.

HPHT has been used since the 1950s, originally for industrial diamonds. It's now refined enough to produce gem-quality stones with consistent clarity and colour.

CVD: growing diamonds from gas

CVD is the newer and increasingly dominant method. A diamond seed is placed in a chamber filled with carbon-rich gas, usually methane, at low pressure. The chamber is heated to around 800°C, which ionises the gas into plasma. Carbon atoms break free and begin depositing on the seed, building the crystal one atomic layer at a time.

CVD produces diamonds with fewer internal strain patterns than HPHT, which is one reason it's become the preferred method for high-quality gem production. The process takes roughly two to four weeks per stone.

After growth: cutting and certification

Once grown, lab-grown diamonds go through the same cutting and polishing process as mined diamonds. They're graded by independent gemological laboratories, in our case IGI (International Gemological Institute), on cut, clarity, colour and carat. An IGI certificate accompanies every centre stone of one carat and up.

Why this matters

Understanding how lab-grown diamonds are made helps answer the most common question: are they real? The answer is yes. Both are carbon, and in both the carbon sits in the crystal structure that makes a diamond hard and bright. What differs is where it grew. Telling them apart takes equipment that reads trace elements, not a loupe.

If you'd like to see what lab-grown diamonds look like set in a ring, explore our solitaire lab-grown diamond rings or read our diamond education guide.

Ready to see lab-grown diamonds in person? Our most popular designs include solitaire rings, a single lab-grown diamond in solid 18K gold or platinum, alongside distinctive shapes like oval cut, emerald cut, and marquise. Each ring is handcrafted to order, and centre stones of one carat and up are IGI certified.

Explore Una Diamond Engagement Rings

Every Una Diamond ring is handcrafted to order in solid 18K gold or platinum and delivered in around six weeks. Centre stones of one carat and up are IGI certified: