· 8 min read
CVD vs HPHT Lab Grown Diamonds: Does the Method Matter?
CVD vs HPHT lab grown diamonds compared using GIA research: how each is grown, what the report tells you, and when the growth method should matter.
CVD and HPHT are two ways of growing a diamond in a lab, and both produce real diamond with the same chemistry and crystal structure as a mined stone. Once a stone is cut, graded and set, the growth method does not decide how it looks. Colour, clarity and cut grades do that. The method is still worth knowing, because it tells you what kinds of inclusions to look for and whether the stone has probably had a colour treatment after growth.
Below is what the grading labs have actually published on the two methods, what that means for a stone you might buy, and where the difference stops mattering.
How each method grows a diamond
Both methods start with a small diamond seed and add carbon to it until a larger crystal forms. The conditions are very different.
HPHT: high pressure, high temperature
GIA describes HPHT as a process where the growth chamber is "heated to 1300-1600 °C with pressures above 870,000 pounds per square inch" (GIA, HPHT and CVD Diamond Growth Processes). A carbon source such as graphite dissolves in a molten metal flux of iron, nickel or cobalt. The carbon then moves through the flux and crystallises on the seed. GIA says this "occurs over a period of several days to weeks."
The crystals that come out "typically have cubic faces in addition to octahedral ones." Natural diamonds grow as octahedra, so that cubic shape is one of the clues a lab uses.
CVD: chemical vapour deposition
CVD runs at lower pressure. GIA describes a vacuum chamber filled with hydrogen and a carbon gas such as methane, heated to "about 900-1200°C". An energy source such as a microwave beam breaks the gas down, and carbon atoms settle onto flat diamond seed plates. GIA says "the entire growth process can take three or four weeks", and the result is "flat, tabular crystals" (GIA).
GIA also notes that CVD needs a "lower upfront equipment cost than HPHT". That is a fact about factories. It does not mean a CVD stone will be cheaper than an HPHT stone of the same grade.
What the growth method leaves behind in the stone
This is where the difference becomes practical. Each method tends to leave its own kind of inclusion and its own colour problem.
- HPHT stones "often contain metal flux inclusions" containing "elements such as iron, nickel and cobalt" (GIA). These are bits of the molten metal the diamond grew in. In a higher clarity grade they are tiny. In a lower grade they can be dark and easier to spot.
- CVD stones "do not have metallic inclusions. Rather, they often contain dark graphite inclusions," according to the same GIA page.
- Colour after growth: GIA says CVD crystals are typically brown when they come out of the chamber and are often "decolorized by HPHT annealing." So many CVD stones have been through an HPHT press too, just as a treatment rather than as the growth method.
That last point is the one most buyers miss. GIA's researchers reported in 2024 that "Among CVD-grown diamonds submitted to GIA, ~80% have been subjected to post-growth HPHT treatment to improve their color grade" (Eaton-Magaña, Hardman and Odake, Gems & Gemology, Summer 2024). "CVD vs HPHT" is often not an either-or. A typical colourless CVD stone has had both.
CVD and HPHT side by side
| HPHT-grown | CVD-grown | |
|---|---|---|
| Growth conditions (GIA) | 1300-1600 °C, above 870,000 psi | About 900-1200 °C, lower pressure |
| Growth time (GIA) | Several days to weeks | Three or four weeks |
| Rough crystal shape | Cubic plus octahedral faces | Flat, tabular |
| Typical inclusions | Metal flux (iron, nickel, cobalt) | Dark graphite |
| Common post-growth step | Treatment possible, depending on colour | Often HPHT annealing to remove brown |
| Visible to the naked eye once cut and graded | No reliable difference | No reliable difference |
The last row is the honest summary. GIA's consumer guide says lab-grown diamonds "appear the same to the unaided eye as natural diamonds of comparable quality," and "only a gemological lab with advanced testing equipment can authoritatively determine whether a diamond is natural or synthetic" (GIA 4Cs, Lab-Grown Diamond Jewelry). If a lab needs specialised equipment to tell lab-grown from natural, you are not going to tell CVD from HPHT across a dinner table.
How the market has shifted
The mix of stones for sale today is not what it was ten years ago, and older advice can mislead you.
GIA's 2024 research update says CVD submissions "eventually outnumbered HPHT-grown submissions by around 2016," and that "CVD products now dominate the supply of laboratory-grown diamonds submitted for grading reports" (Gems & Gemology, Summer 2024). The same paper reports that colourless stones now make up most HPHT submissions too, with more than 90% of HPHT-grown intake colourless in 2021 to 2023.
A few things follow from that:
- Older articles saying "HPHT stones are yellowish" or "CVD stones are always brown" describe stones from earlier years. Both methods now produce colourless diamonds.
- The paper also notes that "Colorless to near-colorless laboratory-grown diamonds are type II, meaning they have no detectable nitrogen impurities." That applies to both methods. Neither one is chemically "purer" in a way you could see in a ring.
- Both methods now reach large sizes. GIA reports a 75.33 ct faceted CVD stone in 2024. So size alone does not point to one method.
What your grading report tells you
GIA, when it introduced its Laboratory-Grown Diamond Report in 2020, said "The new LGDR reports state that the stone was created by either the chemical vapor deposition (CVD) or high pressure, high temperature (HPHT) method and whether it may include post-growth treatments to change the color" (GIA, GIA Gets Specific on Laboratory-Grown Diamonds, 2020).
GIA has since changed how it describes quality. From 1 October 2025, GIA stopped using the D-to-Z and Flawless-to-I3 scales for lab-grown stones and moved to two categories, "Premium" and "Standard" (GIA, August 2025). Premium requires D colour, "Very, Very Slightly included and higher" clarity and Excellent polish and symmetry. Standard covers "E-to-J" colour and at least "Very Slightly included" clarity. GIA says "Any diamond that does not meet all the minimum criteria for 'Standard' will not receive a GIA assessment." GIA explained the change by saying "more than 95% of laboratory-grown diamonds entering the market fall into a very narrow range of color and clarity" (GIA, June 2025).
Other labs grade lab-grown stones in their own formats, and the details vary. Don't assume one lab's report reads like another's. Look at the report for your specific stone and find two lines: the growth method, and any note about post-growth treatment. If neither line is there, ask the seller.
On wording, the US Federal Trade Commission's guidance says a lab-grown stone should be described with "'laboratory-grown,' 'laboratory-created,' '[manufacturer name]-created,' or some other word or phrase of like meaning" placed before the word "diamond" (FTC, In the Loupe, 2019). The same FTC guidance says sellers should disclose treatments that are not permanent, that need special care, or that significantly affect value. That is US guidance, not Canadian law, but it is a fair standard to hold any seller to.
When the growth method should change your decision
Most of the time it shouldn't. Here is how I would weigh it, in order:
- Cut first. On a round, the cut grade decides most of the sparkle. A well-cut CVD stone will outshine a poorly cut HPHT stone, and the reverse is just as true.
- Colour and clarity next, read from the report. Whatever the method, an eye-clean stone in the colour range you are happy with is the goal. Note that a lab's Standard band covers a wide spread of colour, so look at the exact grade or details if the report gives them.
- Check the inclusion type at lower clarity. This is where the method shows up. At lower clarity grades, a dark metallic flux inclusion in an HPHT stone or a dark graphite inclusion in a CVD stone can be visible. Ask for magnified images and check where the inclusion sits. Under a prong is fine. Under the table is not.
- Treatment disclosure. A post-growth HPHT anneal on a CVD stone is normal and, from what has been published, it is not a reason to avoid a stone. You should still know about it, and the report should say so.
- Price last. If two stones with the same grades and similar images differ in price, do not pay extra for one method. Nothing published by the grading labs supports paying a premium for CVD over HPHT or the other way round.
The plain answer is that paying more for a specific growth method is not worth it. Pay for cut and an eye-clean stone. Some sellers market one method as superior. GIA's own growth-process page makes no claim that either is better, and I would not either.
What the evidence doesn't settle
To be fair about the limits:
- No grading lab publishes data showing that CVD or HPHT stones wear, chip or hold their polish differently once set. Both are diamond.
- GIA's 2024 paper notes "there is no cost-effective or rapid screening tool that can definitively identify all laboratory-grown diamonds." Identifying the method takes lab equipment, which is why the report matters more than any sales claim.
- Grading is still done by people and machines making judgement calls at the boundaries. Two stones with the same report can look slightly different. Images and video of the actual stone remain your best check.
What to do next
Start in our loose diamond search and filter for lab-grown stones in the cut, colour and clarity you want. Treat the growth method as a detail to confirm, not a filter to start with. Open the report for each stone you shortlist, check the growth method and any treatment note, and look at the magnified images for where the inclusions sit.
Then choose a setting from our engagement ring settings, preview the pair in 3D, and finish the ring with your metal, size and engraving. If you are still weighing lab-grown against natural, our other guides cover value, certification and colour grades in more depth.
Sources
- Gemological Institute of America (GIA). "HPHT and CVD Diamond Growth Processes: Making Lab-Grown Diamonds." 2016. GIA
- Eaton-Magaña, S., Hardman, M. F., and Odake, S. "Laboratory-Grown Diamonds: An Update on Identification and Products Evaluated at GIA." Gems & Gemology, Vol. 60, No. 2, Summer 2024. GIA Gems & Gemology
- GIA. "GIA Gets Specific on Laboratory-Grown Diamonds." Press release, 13 October 2020. GIA
- GIA. "GIA to Use New Descriptive Terminology for Laboratory-Grown Diamonds." Press release, 2 June 2025. GIA
- GIA. "GIA Launches Updated Laboratory-Grown Diamond Services October 1." Press release, 26 August 2025. GIA
- GIA 4Cs. "Lab-Grown Diamond Jewelry: What are Synthetic Diamonds?" 2016. GIA 4Cs
- US Federal Trade Commission. "In the Loupe: Advertising Diamonds, Gemstones and Pearls." 2019. FTC