# CVD vs HPHT Diamonds: How They Differ and What to Check

> CVD and HPHT are two ways to make a lab grown diamond. We found no GIA ranking of either: check the finished stone and the growth and treatment lines on its report.

Canonical: https://mazimo.ae/journal/cvd-vs-hpht-lab-grown-diamonds

Diamonds · Published 24 October 2026 · 13 min read · Mazimo Jewellery, Dubai

CVD vs HPHT diamond comes down to how a lab grown crystal was made, not what it is: both processes make real diamond. HPHT grows it from carbon dissolved in molten metal inside a press, and CVD grows it from gas in a vacuum chamber. None of the GIA pages we read ranks one above the other. What matters is the finished stone and what its report says about growth and any treatment after it.

At a glance

- GIA describes both processes as growing carbon onto a diamond seed: HPHT (high pressure, high temperature) uses molten metal in a press, and CVD (chemical vapour deposition) uses a carbon-containing gas in a chamber.
- We found no GIA statement that ranks one process above the other, and GIA's 2024 update shows that both routes deliver colourless stones.
- HPHT is also a treatment: heating after growth is used to remove brown from CVD stones, and GIA says about 80 percent of the CVD stones sent to it since 2020 had post-growth processing, so growth and treatment are separate lines on a report.
- The IGI reports we read state the process and a treatment comment; GIA's Premium or Standard assessment for colourless stones, as announced in 2025, mentions neither; its coloured diamond reports assess both.
- Our ring pages state no growth process or treatment, so ask any seller, including us, whether your stone has a report and what it says.

Sources checked 20 October 2026. IGI's web pages refuse automated requests, so we read its tester page (24 May 2022) and carat weight page (28 July 2023) in a browser on 24 October 2026; the IGI report wording comes from two reports we opened as files. We have not checked UAE disclosure rules.

## CVD vs HPHT diamond: the short answer

HPHT and CVD are two routes to the same material, and both start from a diamond seed. This is our full guide to the two processes; our [lab grown diamond pros and cons guide](https://mazimo.ae/journal/lab-grown-diamond-pros-and-cons) keeps a shorter summary.

| Point | HPHT | CVD |
| --- | --- | --- |
| Where the carbon comes from | A solid source such as graphite, dissolved in molten metals such as iron, nickel or cobalt | A carbon-containing gas such as methane, mixed with hydrogen |
| How a run goes | One uninterrupted run | Can be run in a series of growth steps |
| Colour to manage | Nitrogen, which turns diamond yellow, is kept out | A brown tint, often removed by heating after growth |
| Features GIA's 2016 article lists | Metal flux inclusions, cross-shaped fluorescence, no strain pattern or a weak banded one | Dark graphite or other mineral inclusions, striped fluorescence, banded strain |
| Colour of stones of 4 ct and up sent to GIA | D was the most common colour | E was the most common colour; the majority were colourless, D to F |

Rows follow [GIA's 2016 article](https://www.gia.edu/hpht-and-cvd-diamond-growth-processes) and [GIA's Summer 2024 update](https://www.gia.edu/gems-gemology/summer-2024-gia-update-on-laboratory-grown-diamonds). The last row describes large stones sent to GIA, not the whole market. The features row is from the 2016 article: GIA's 2024 update says it has seen CVD stones without the traditional features and patterns, fluorescence included, and that HPHT stones with strain, though rare, have been reported, and it stresses not relying on one feature alone.

## How each process grows a diamond

HPHT recreates deep-earth heat and pressure in a press, while CVD builds the crystal from gas at far lower pressure. GIA's 2016 article says HPHT heats a chamber holding a diamond seed to between 1,300 and 1,600 °C while carbon dissolves in a molten flux of metals such as iron, nickel or cobalt, which lowers the temperature and pressure needed. Carbon crystallises on the seed over several days to weeks.

[GIA's consumer page](https://4cs.gia.edu/en-us/laboratory-grown-diamond/) puts the pressure at 5 to 6 GPa, which it says is the equivalent of a depth of 150 to 190 km underground. The 2016 article says above 870,000 pounds per square inch; our arithmetic: 870,000 × 6,895 pascals is about 6 GPa, the top of the consumer page's range, so the two pages agree only roughly.

For CVD, the 2016 article describes a vacuum chamber filled with a hydrogen and carbon-containing gas such as methane. Microwaves turn the gas into a plasma, and carbon deposits on flat diamond seed plates. The crystals are removed every few days so the top face can be polished, and the whole process can take three or four weeks. [GIA's 2024 update](https://www.gia.edu/gems-gemology/summer-2024-gia-update-on-laboratory-grown-diamonds) gives size dependent figures: an hour to a few weeks for HPHT, and 40 to 45 days for one 17 ct CVD crystal. The sources differ on temperature: about 900 to 1,200 °C in the 2016 article, and 700 to 1,200 °C on the consumer page. We found no explanation for the gap, so we give both.

On history, [ASME records](https://www.asme.org/topics-resources/content/asme-landmark-made-diamonds-using-heat-and-pressure) that H. Tracy Hall of General Electric produced the first verifiable synthetic diamond by reproducible means, using heat and pressure, on 16 December 1954. GIA's 2016 article calls CVD the newer method, but [its 2024 update](https://www.gia.edu/gems-gemology/summer-2024-gia-update-on-laboratory-grown-diamonds) says CVD was developed earlier and that the first gem-quality lab grown diamonds came from HPHT, so we do not rank the two by age.

## Are CVD and HPHT diamonds real diamonds?

Yes. [GIA says](https://4cs.gia.edu/en-us/laboratory-grown-diamond/) lab grown and natural diamonds are built from the same tightly bonded carbon crystal and are almost identical in chemistry, optics and physical behaviour. The key difference is growth history, which laboratory instruments can detect. Our [moissanite comparison](https://mazimo.ae/journal/moissanite-vs-lab-grown-diamond) covers a material that is not diamond. See also our guide to [lab grown and natural diamonds in the UAE](https://mazimo.ae/journal/lab-grown-vs-natural-diamonds-uae).

## HPHT treated CVD: when one stone has both

An HPHT treated CVD diamond was grown by CVD and then heated in an HPHT machine to improve its colour. GIA's 2024 update adds that low-pressure, high-temperature annealing can also change the colour of CVD stones, so ask which treatment the report means.

A [GIA lab note from Summer 2020](https://www.gia.edu/gems-gemology/summer-2020-labnotes-laboratory-grown-diamonds-low-color-grades) says CVD diamonds grown with nitrogen added or at a high growth rate end up brown, and HPHT treatment after growth is commonly used to improve the colour. The 2024 update says that since 2020 about 80 percent of the CVD stones sent to GIA had post-growth processing. [GIA's 2014 page on diamond treatments](https://4cs.gia.edu/en-us/blog/diamond-treatments-mean/) adds that HPHT treatment uses machines essentially like those that grow synthetic diamonds, can turn some brownish diamonds colourless, and is considered permanent.

The 2020 note also describes 11 treated CVD stones of 1.02 to 1.33 carats whose colour stayed low, about J; the note says the low grades are believed to be linked to the length of the treatment.

Our reading: ask whether the paperwork states the treatment, since GIA's 2014 treatments page calls the HPHT process permanent (it does not say whether it means natural or lab grown stones) and says all treatments should be disclosed before purchase. Beyond the 2020 note we found no GIA or IGI statement comparing treated and untreated lab grown stones, so we make no claim.

## Which is better, CVD or HPHT?

We found no GIA statement that ranks one process above the other, and GIA's 2024 update shows both routes produce colourless stones, so the finished stone and its report decide.

The 2024 update does not compare clarity, and we found no GIA or IGI statement that favours either process on durability or sparkle.

These checks separate two stones, in this order:

1. **The finished colour and clarity**, or GIA's Premium or Standard assessment. Our [4Cs guide](https://mazimo.ae/journal/diamond-4cs-guide) and [colour grade and fluorescence guide](https://mazimo.ae/journal/diamond-colour-grade-and-fluorescence) explain what to pay for.
2. **Cut, polish and symmetry**, which decide the light. See our [cut grade guide](https://mazimo.ae/journal/diamond-cut-grade-excellent-vs-ideal).
3. **The growth line and the treatment line**, if the report has them (next section).
4. **Millimetres and exact weight**, because two stones of one weight can differ in size; [IGI says](https://www.igi.org/consumer-education/diamond-4cs/carat-weight/) this is why its reports list length, width and depth. Our [diamond size chart](https://mazimo.ae/journal/diamond-size-chart-carat-mm) shows sizes by shape.

## What a lab grown report says about the growth process

GIA's laboratory grown diamond report and the IGI lab grown reports we read name the growth process, but the wording differs, and not every GIA report type does: GIA's [report FAQ](https://www.gia.edu/gia-faq-analysis-grading-laboratory-grown-report-cvd-hpht) says three of its four types carry a growth method comment, and its [page on what changed](https://www.gia.edu/gia-faq-what-changed-lab-grown-diamond-report) says the Dossier report no longer offers growth type or treatment options (neither page shows a date). For colourless to near-colourless stones GIA's format changed on 1 October 2025; [its coloured diamond reports](https://www.gia.edu/gem-lab-service/laboratory-grown-diamond) still carry growth and treatment lines. The dated rows are single examples, not a survey, and we do not link other people's stones.

| Report | Growth process | Post-growth treatment |
| --- | --- | --- |
| GIA laboratory grown diamond report dated 16 February 2021 | Comment names CVD as the growth process | Says there is evidence of post-growth treatment to change the colour |
| GIA quality assessment (colourless to near-colourless), from 1 October 2025 | Not mentioned in GIA's announcement or the fee schedule's quality assessment section | Not mentioned in either |
| GIA coloured diamond reports, per the fee schedule effective 1 July 2026 | Include an assessment of growth type | Include an assessment of post-growth treatment |
| IGI report dated 13 October 2024 | Names HPHT | States the stone is as grown, with no indication of post-growth treatment |
| IGI report dated 15 October 2025, a fancy colour stone | Names CVD | States indications of post-growth treatment |

GIA's [report page](https://www.gia.edu/introducing-lgdr-by-gia), which dates the redesigned format to October 2020, says its laboratory grown diamond report states CVD or HPHT, and whether evidence of post-growth colour treatment was detected, not detected or undeterminable.

The second row rests on the [GIA announcement of 26 August 2025](https://www.gia.edu/gia-news-press/updated-laboratory-grown-diamond-services-to-launch-october-1) and the quality assessment section of GIA's [fee schedule effective 1 July 2026](https://www.gia.edu/dam/jcr:665d405e-7d16-4877-8cae-9190e8a2ae44/Lab-Grown__FeeSchedule_MASTER_Q3%202026_USD.pdf); neither mentions growth method or treatment. That does not prove the new document omits them, so read the document you are given.

The fee schedule also lists a colour treatment letter, an add-on that describes the specific treatment method; its add-on list is headed as covering lab grown and lab grown coloured diamonds, and we did not check when GIA issues one.

Our [guide to IGI and GIA reports in Dubai](https://mazimo.ae/journal/diamond-certificates-igi-gia-dubai) reads a report line by line, and our standing guides cover [GIA reports](https://mazimo.ae/guides/gia-diamond-reports) and [IGI reports](https://mazimo.ae/guides/igi-diamond-reports). GIA's fee schedule lists a GIA laboratory in Dubai (GIA Laboratory FZCO, Uptown Tower); we did not check its services.

## Can a tester or your eye tell CVD from HPHT?

Not reliably. We found no source that says the eye or a handheld tester separates CVD from HPHT. [GIA says](https://4cs.gia.edu/en-us/laboratory-grown-diamond/) its laboratory can tell whether a lab grown stone was made by HPHT or CVD using spectroscopy and other testing methods.

[IGI's article of 24 May 2022](https://www.igi.org/diamond-detection-and-handheld-testers/) says thermal testers make no distinction between lab grown and natural diamond, and that an electrical tester can wrongly read some lab grown diamonds as moissanite, and links this to traces of the metal catalyst used in HPHT growth, which can let current pass through the stone. Our reading: no tester reading establishes the growth process, and IGI quotes a device maker saying informal detection is no substitute for laboratory analysis, so ask for the report. Our guide to [whether lab grown diamonds pass a diamond tester](https://mazimo.ae/journal/do-lab-grown-diamonds-pass-a-diamond-tester) goes through each tool.

## Choosing a ring, then asking about the process

Choose the ring and the finished stone first, then ask which process grew it and whether it was treated afterwards. Three questions settle that in one message to any seller, including us on WhatsApp: whether the stone has a laboratory report and, if so, which laboratory issued it and its number; what its comment line says about the growth process; and what it says about post-growth treatment, with the method if the report gives one.

For scale, the centre stone of the Round Solitaire Ring, 2 ct is about 8.05 × 8.07 mm, which spans about 49 percent of a UAE size 52 finger (about 16.55 mm across, from 52 / 3.14159; 8.05 / 16.55 = 0.49).

Our rings are made to order in 18K gold, in UAE sizes 46 to 62, and the [ring designer](https://mazimo.ae/design) previews a ring at true size. We can set a lab grown or a natural diamond, and our ring pages state neither the process nor any grade, so tell us which you prefer. The pictures are renders, and camera try-on (see our [camera try-on guide](https://mazimo.ae/journal/try-diamond-ring-on-with-camera-ring-size)) works on all four rings below.

[Round Solitaire Ring, 2 ct, Round · 2 ct](https://mazimo.ae/product/round-solitaire-ring-1-96-ct)[Round Six Claw Solitaire Ring, Round · 2 ct](https://mazimo.ae/product/round-six-claw-solitaire-ring)[Oval Solitaire Ring, 3.5 ct, Oval · 3.5 ct](https://mazimo.ae/product/oval-solitaire-ring-3-06-ct)[Oval Pavé Solitaire Ring, 1.5 ct, Oval · 1.5 ct](https://mazimo.ae/product/oval-pave-solitaire-ring-1-47-ct)

## Questions people ask

### What is the difference between CVD and HPHT diamonds?

CVD grows a diamond from a carbon-containing gas in a chamber at near-vacuum pressure, while HPHT grows it from carbon dissolved in molten metal in a press at very high pressure. Both make real diamond. The practical difference is what the report says about process and treatment.

### Which is better, CVD or HPHT?

We found no GIA statement that ranks them, and GIA's 2024 update shows both routes produce colourless stones. Compare the finished stone, its cut and its size in millimetres, and the growth and treatment lines on its report.

### Are CVD diamonds real diamonds?

Yes. GIA says lab grown diamonds share natural diamond's crystal structure and have nearly the same properties, and the difference is growth history. That covers CVD and HPHT alike.

### What does HPHT treated CVD diamond mean?

It means the stone was grown by CVD and then heated in an HPHT machine to improve its colour, because some CVD crystals come out brown. GIA's 2014 treatments page calls the HPHT process permanent. Ask for the treatment line on the report: it is a separate fact from the growth process.

### Can a diamond tester tell CVD from HPHT?

Not reliably. IGI says thermal testers do not separate lab grown from natural diamond, and that an electrical tester can mistake certain lab grown diamonds for moissanite because of metal left by the HPHT process. GIA says its laboratory identifies the growth method with spectroscopy and other methods, so ask for a report.

### Is a CVD or HPHT diamond cheaper?

No source we read fixes a price gap between the two, and we state no prices. GIA's 2016 article says CVD needs a lower upfront equipment cost, which concerns the grower, not a ring's price. Each ring page shows its price at [our diamond rings](https://mazimo.ae/shop/diamond-rings), and our [engagement ring cost guide](https://mazimo.ae/journal/engagement-ring-cost-dubai-aed-guide) explains how to compare quotes.

### How do I find out which process made my diamond?

If your stone has a laboratory report, read its comments and check its number on the laboratory's own site. The IGI reports we read name the process, and GIA's earlier laboratory grown diamond report did. For colourless stones GIA's 2025 Premium or Standard assessment, as announced, mentions neither, so ask the seller to state the process and any treatment in writing.

**At Mazimo.** We can set either kind of diamond, so tell us which you prefer. Preview a ring at true size in our [ring designer](https://mazimo.ae/design), or read our guide to [designing your own ring in Dubai](https://mazimo.ae/journal/design-your-own-engagement-ring-dubai). Our boutique is at Al Manal Center in Deira, minutes from the Gold Souk, and every ring is hallmarked in Dubai and delivered insured across the UAE at no charge.

Prices and rates mentioned are indicative at the time of writing. For today's number see [today's gold rate](https://mazimo.ae/gold-rates), or [message the boutique](https://mazimo.ae/contact).