How Are Lab Grown Diamonds Made? CVD vs HPHT Explained Simply

Lab grown diamonds are made in one of two ways. CVD (chemical vapour deposition) grows a diamond layer by layer inside a gas-filled vacuum chamber, a bit like 3D printing with carbon atoms. HPHT (high pressure, high temperature) squeezes and heats carbon around a diamond seed until it crystallises, recreating the conditions found more than 150km underground. Both methods produce real diamonds, chemically identical to mined stones and graded on exactly the same scale. Here is how each one works, in plain English, and what (if anything) the method means for the ring on your finger.

In this article

• What every lab grown diamond starts with
• What does CVD mean and how does it work?
• What does HPHT mean and how does it work?
• CVD vs HPHT: which method makes better diamonds?
• How long does it take to grow a diamond?
• Does the growing method matter when you buy?
• FAQ

What every lab grown diamond starts with

Whichever method you use, it starts with a seed: a wafer-thin slice of existing diamond that serves as the blueprint the new crystal will copy. Carbon atoms latch onto that seed and extend its lattice, one atom at a time, until there is a rough diamond where the slice used to be. Get the seed right and control the conditions around it precisely, and you get a fine stone; get either wrong and you do not. From there on, a lab grown rough is treated exactly like a mined one, cut, polished and graded the same way.

What does CVD mean and how does it work?

CVD is short for chemical vapour deposition, and it grows most of the gem-quality lab diamonds on the market today. Picture a flat seed plate sitting inside a sealed vacuum chamber. Fill that chamber with hydrogen and a carbon-rich gas like methane, then fire microwaves through it until the gas ignites into a glowing plasma. The plasma tears the gas molecules apart, freeing their carbon, and that carbon rains gently down onto the cooler seed, settling into place and thickening the crystal week by week.

What comes out is a flat, tabular slab edged with rough graphite that gets trimmed off. A lot of CVD stones then get a quick HPHT treatment to tidy up their colour before they are cut. The payoff is a Type IIa diamond, the purest category there is, and one so uncommon in nature that barely 1% of mined diamonds make the grade.

What does HPHT mean and how does it work?

HPHT, high pressure high temperature, is the older technique. It is how the very first lab diamonds were grown back in the mid-1950s. There is no gas involved this time. Instead you seal solid carbon (usually graphite) together with a metal catalyst, iron, nickel or cobalt, and a diamond seed inside a capsule, and then you put that capsule inside an enormous press.

From there the press simply imitates the earth. It heats the capsule to somewhere between 1,300 and 1,600 degrees Celsius and crushes it at 5 to 6 gigapascals, a pressure GIA likens to balancing a passenger jet on a fingertip. The metal liquefies, swallows the carbon, and that carbon settles onto the cooler seed as diamond. CVD leaves you with flat plates; HPHT grows blockier cuboctahedral crystals that look far more like natural rough.

CVD vs HPHT: which method makes better diamonds?

The honest answer is neither, and anyone insisting one method is flatly better is usually trying to sell you something. Each grows real diamonds, each can hit the very top grades, and IGI and GIA judge both on the identical 4Cs, noting the growth method on the certificate either way. The gaps between them are tendencies, not a scoreboard.

	CVD	HPHT
How it works	Carbon gas deposits on a seed in a vacuum chamber	Carbon crystallises around a seed under extreme pressure and heat
Conditions	Moderate pressure, around 800 to 1,200C	5 to 6 GPa, 1,300 to 1,600C
Typical growth time	Several weeks	Days to weeks
Rough crystal shape	Flat, tabular plates	Chunky cuboctahedron
Typical quirks	May need post-growth colour treatment	Can carry tiny metallic traces from the catalyst
First achieved	1950s (gem quality from the 2000s)	Mid-1950s (the original method)

What actually varies is the individual stone. A poorly grown CVD diamond and a poorly grown HPHT diamond are both poor; a superbly grown example of either is superb. Which is why the certificate, and the person choosing the stone, matter far more than the machine that grew it.

How long does it take to grow a diamond?

Typically between a few days and eight weeks, depending on the method and the target size. HPHT is the faster process, often producing a rough crystal in days; CVD usually takes four to six weeks, partly because the crystals are periodically removed and cleaned of graphite so they keep growing as a single stone. Then add cutting, polishing, grading and certification.

Compare that with the one to three billion years a mined diamond spends forming, and the several months a made-to-order ring might spend in a traditional supply chain, and "grown in weeks" starts to sound less like a shortcut and more like the entire point.

Does the growing method matter when you buy?

For your eyes, your budget and your grandchildren's inheritance: no. The method appears as a line on the grading report, and nothing about it changes how the diamond looks, wears or lasts. What should drive your decision is the same as it ever was: the 4Cs on the certificate, the quality of the cut above all, and whether someone with taste and accountability selected the stone.

That last part is the Not Mined difference. We do not buy blind parcels; every diamond is hand-picked, certified by IGI or GIA, and set to order in 18ct hallmarked gold. If you want the deeper value case, our guide to whether lab grown diamonds are worth it covers pricing, resale and ethics honestly.

Frequently asked questions

Are CVD diamonds real diamonds?

Yes. A CVD diamond is pure crystallised carbon with the same hardness, brilliance and chemistry as a mined diamond. It passes standard diamond testers and is graded by IGI and GIA on the same scale as any other diamond.

Which is better, CVD or HPHT?

Neither method is inherently better. Both can produce top-grade diamonds and both can produce poor ones. Judge the individual stone by its certificate, especially its cut grade, rather than by the machine that grew it. View engagement rings →

How long does it take to grow a 1 carat diamond?

Roughly two to eight weeks depending on the method: HPHT is usually faster (days to a few weeks), while CVD typically takes four to six weeks. Cutting, polishing and certification add time after growth.

Can you tell how a lab grown diamond was made?

Not by eye. Gemmological laboratories identify the growth method using spectroscopic analysis, and reputable certificates state the method in the report's additional information. Your certificate will tell you; your eyes never will.

Do lab grown diamonds start from a seed?

Yes. Both CVD and HPHT begin with a diamond seed, a thin slice of existing diamond that provides the crystal template. New carbon atoms extend that structure until a rough diamond has grown around it.