CVD vs HPHT lab diamonds: which is better?

Quick answerUpdated October 2026

Neither CVD nor HPHT is better: both grow real diamond, and a finished colourless stone does not show by eye which method made it, so judge it by its grading report. Most CVD stones are HPHT-treated after growth to improve colour (about 80 percent of those GIA sees), so check the report’s comments for the growth method and any treatment.

What is an HPHT diamond?

An HPHT diamond is a lab-grown diamond made by high pressure and high temperature, in a press that copies the conditions deep in the earth. GIA describes the process: carbon dissolves in a molten flux of metals such as iron, nickel or cobalt at 1,300 to 1,600 °C and more than 870,000 pounds per square inch (about 6 gigapascals), then moves through the flux to a cooler diamond seed and crystallises on it over several days to weeks. Each crystal grows in a single uninterrupted run. Because the carbon travels through molten metal, an HPHT stone can trap metallic flux , which look black in transmitted light and metallic in reflected light; GIA notes that a stone with enough of them can be picked up with a magnet. Most early HPHT stones were strongly coloured, often yellow or yellow-orange from nitrogen, but more than 90 percent of the HPHT diamonds GIA received from 2021 to 2023 were colourless. GIA also says most lab-grown melee (very small diamonds) comes from makers in China, where HPHT is the preferred way to grow small diamonds economically. For the presses themselves, see how lab gems are grown.

What is a CVD diamond?

A CVD diamond is a lab-grown diamond made by chemical vapour deposition. Flat diamond sit in a vacuum chamber filled with hydrogen and a carbon-bearing gas such as methane, heated to about 900 to 1,200 °C. A microwave beam turns the gas into a cloud, and carbon from it settles on the seed plates, building the crystal in thin layers. GIA says CVD works at moderate pressure, costs less in equipment up front than HPHT, and can be run as a series of growth steps rather than one continuous run. CVD stones have no metallic inclusions, though they often hold dark specks of graphite. Many come out of the chamber brownish, a colour GIA links to clusters of missing atoms or nitrogen-related defects in the crystal, which is why most are treated afterwards (see below). CVD is now the method behind most lab diamonds sent to GIA for grading: it overtook HPHT around 2016, and GIA now averages more CVD stones a day than it once received in a whole year.

How do CVD and HPHT diamonds compare?

	HPHT	CVD
What it is	Diamond	Diamond
How the carbon gets there	Dissolved in molten iron, nickel or cobalt, then crystallised on a diamond seed	Deposited from a hydrogen and methane plasma onto flat diamond seed plates
Growing conditions	1,300 to 1,600 °C and more than 870,000 psi	About 900 to 1,200 °C at moderate pressure in a vacuum chamber
Growth	One uninterrupted run	Can be grown in a series of steps
Typical inclusions	Metallic flux; a stone with enough of it can be picked up with a magnet	No metal; often dark graphite
Under ultraviolet (a lab test)	Cross-shaped ; colourless stones usually glow an intense blue-green for a long time after the lamp goes off	Striated fluorescence; growth layers show under deep ultraviolet
Straight out of growth	Mostly colourless today; over 80 percent of the D-to-Z stones GIA has seen since 2020 carry boron detectable in the infrared	Often brownish
Treatment after growth	Colours such as pink and red can be made by treatment with radiation and heat, which GIA calls less common	About 80 percent of those GIA sees were HPHT-treated to improve colour
Commonest colour grade among large (4 ct and up) stones at GIA	D	E
Where it leads	Small stones: most lab-grown melee comes from China, where HPHT is preferred	Volume: most lab diamonds sent for grading
Better?	Neither: judge the grade	Neither: judge the grade

The facts in the table are from GIA: its 2016 explainer on HPHT and CVD growth and the Summer 2024 Gems & Gemology review of the lab-grown diamonds GIA has examined. GIA says a trained gemologist can sometimes recognise the method with standard gem-testing equipment, and that otherwise it takes advanced scientific instruments. It also says no rapid, low-cost screening tool identifies every lab-grown diamond, and it advises against relying on any single observation when testing colourless HPHT-grown stones. Telling the methods apart is laboratory work, not something to judge by eye.

Why are most CVD diamonds treated after growth?

Because growing fast and fixing the colour afterwards can be quicker or cheaper than growing a colourless crystal directly. GIA reports that about 80 percent of the CVD diamonds submitted to it have been HPHT-treated after growth to improve their colour grade. Growers can use recipes that build diamond layers quickly, accept a brownish crystal, and then anneal the brown out, which GIA says may be faster, easier or more cost-effective than growing a colourless CVD crystal directly. GIA’s 2016 explainer goes further: most colourless CVD diamond on the market was probably brown once. Note that the letters HPHT mean two different things here. HPHT growth makes a diamond; HPHT treatment is a heat treatment applied to a crystal that has already grown, which GIA says runs hotter than HPHT growth, above 1,600 °C, and adds no new diamond. So an HPHT-treated CVD diamond is still a CVD diamond, and still diamond. In the US, the FTC Jewelry Guides say a gem name used for a lab-grown stone must be immediately preceded by words such as "laboratory-grown" or "laboratory-created", so it is clear the stone was not mined (16 CFR 23.25, which the diamond section, 23.12, points to for lab-created diamonds). Nothing in those sections asks a seller to name CVD or HPHT, and the treatment rule (16 CFR 23.24) calls for disclosure only when a treatment is not permanent, creates special care needs or has a significant effect on value. A listing may mention neither, so the report is where to look. For treatments on other stones, see gem treatments.

What should you check when buying a CVD or HPHT diamond?

Judge the stone, not the method. The report. Buy a lab diamond with an IGI or GIA report number and type the number into the laboratory’s own site yourself: see how to check a diamond report number. The comments. IGI says the growth process and any treatment are noted in the comments section of its lab-grown report on request, and that in some cases a report names the method as HPHT or CVD. If the comments say nothing about either and it matters to you, ask the seller before you buy. The grade and the measurements. Colour, clarity, cut and size decide how the stone looks, whichever way it was grown. A GIA lab-grown report issued since 1 October 2025 gives "Premium" or "Standard" instead of colour and clarity letters, while IGI still gives full grades: see IGI vs GIA for lab-grown diamonds. The price. If two stones share a grade and similar measurements, choose on price and setting, not on method. For what a stone should cost, see how much a 1 carat lab-grown diamond costs.

Frequently Asked Questions

Is a CVD diamond a real diamond?

Yes. The FTC Jewelry Guides define diamond as a mineral of essentially pure carbon crystallised in the isometric (cubic) system (16 CFR 23.12), and a CVD diamond is exactly that, as is an HPHT diamond. Under the same Guides (16 CFR 23.25), both should be sold as laboratory-grown, laboratory-created or similar, because neither was mined.

Can a jeweller tell a CVD diamond from an HPHT diamond?

Not by eye. GIA says a trained gemologist can sometimes tell with standard gem-testing equipment, and otherwise it takes laboratory instruments. Signs GIA lists as typical of HPHT include metallic flux inclusions and, in colourless stones, an intense, long-lasting blue-green glow after ultraviolet. Signs of CVD include growth layers under deep ultraviolet and a silicon-vacancy signal near 737 nm, though GIA now finds that signal weak or missing in more CVD stones. GIA advises against relying on any single observation.

Is an HPHT-treated CVD diamond worse than an untreated one?

Not in itself. GIA reports that about 80 percent of the CVD stones it sees were annealed this way to improve their colour grade, and the treated stone is still diamond. What matters is the grade on the report, so compare stones by grade and measurements, and look for the treatment note in the report’s comments.

Which method makes coloured lab diamonds?

Both can. GIA notes that boron in HPHT growth gives blue crystals, that early HPHT stones were often yellow or yellow-orange from nitrogen, and that colours such as pink and red can be produced by treatment after growth. GIA’s 2024 review also describes pink and blue CVD-grown stones.

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