CVD vs HPHT Lab Grown Diamonds: Does the Growing Method Matter?

Once you start researching lab grown diamonds, you inevitably come across two acronyms: CVD and HPHT. The question of which is better follows quickly. The short answer is that both are real diamonds, chemically, physically and optically identical to mined diamonds. The growth method does not make one lesser.

This guide explains both methods plainly and shows why, for the buyer, the certified 4Cs of the individual stone matter far more than the label.

What Is a CVD Lab-Grown Diamond?

Chemical Vapour Deposition, or CVD, is the newer of the two methods. A thin diamond seed, a slice of diamond, is placed in a vacuum chamber filled with a carbon-rich gas such as methane mixed with hydrogen. A microwave energy source heats the gas into a plasma, breaking the molecules apart so carbon atoms deposit onto the seed layer by layer.

Per GIA, diamonds grow from a hydrocarbon gas mixture subjected to moderate pressures and temperatures in a vacuum chamber. The chamber is heated to about 900-1200°C. A microwave beam causes carbon to precipitate out of a plasma cloud and deposit onto a seed crystal. The crystal grows in one main direction into a flat, tabular shape.

The entire growth process can take three or four weeks, often with stop-start cycles to polish away non-diamond carbon. CVD diamonds are typically Type IIa, the purest diamond classification, containing no detectable nitrogen. Fewer than 2 per cent of natural diamonds qualify as Type IIa. CVD diamonds do not contain metallic inclusions.

What Is an HPHT Lab-Grown Diamond?

High Pressure High Temperature, or HPHT, replicates the conditions deep within the earth. A small diamond seed sits in a press with a carbon source, graphite and a molten metal flux of iron, nickel and cobalt. The flux dissolves the carbon, which migrates to the cooler seed and crystallises.

Per GIA, the growth chamber is heated to 1300-1600 °C with pressures above 870,000 pounds per square inch. HPHT grows in a cuboctahedron shape with 14 growth directions. Growth takes anywhere from several days to a few weeks, depending on the desired size and quality.

HPHT was the first successful method, achieved by General Electric in 1954, initially for industrial use. HPHT stones can contain metallic flux inclusions, which can occasionally make a stone magnetic and were historically prone to a yellow tint from nitrogen or a blue nuance from boron. Technology has advanced significantly and HPHT remains excellent for producing fancy coloured diamonds and top D-colour whites.

CVD vs HPHT: The Key Differences

Does the Growing Method Affect Quality or Beauty?

No. Both CVD and HPHT produce real diamonds which score 10 on the Mohs hardness scale and share identical chemical, physical and optical properties with mined diamonds. Both are graded on the same 4Cs. A well-cut, well-graded diamond of either method looks identical to the naked eye.

In 2018, the US Federal Trade Commission removed the word "natural" from its official definition of a diamond in its revised Jewelry Guides, recognising that lab grown stones have essentially the same optical, physical and chemical properties as mined diamonds. The takeaway is clear: beauty comes from cut quality and the 4Cs, not from the growth acronym.

Colour, Clarity and Inclusions Compared

HPHT historically produced better colour and can reach top D grades directly. CVD often grew with a brownish tint, which is later removed by treatment. Since 2020, approximately 80 per cent of CVD-grown diamonds submitted to GIA have undergone post-growth processing.

HPHT can carry metallic flux inclusions, which appear black with a metallic lustre and may be magnetic. CVD tends toward dark graphite pinpoints and can show banded strain patterns. CVD is typically Type IIa; HPHT is often Type Ib or contains nitrogen. Both can fluoresce, HPHT often more so.

These are tendencies. It is entirely possible to find an HPHT diamond with higher clarity than a given CVD diamond and vice versa.

Do CVD or HPHT Diamonds Get Treated After Growth?

Many CVD diamonds undergo a secondary HPHT annealing step to remove brown colour and improve their appearance. Per GIA Research, "Most laboratory-grown diamonds passing through GIA's laboratories are grown by CVD, with most undergoing post-growth HPHT treatment to remove their color". CVD-grown diamonds with a brown coloration after growth "can be enhanced using HPHT treatments to reduce or remove the brown coloration", conducted at over 1600°C.

This is standard, accepted, permanent and stable. Reputable laboratories disclose it in the comments section of the report. HPHT-grown stones less often need colour treatment. Fancy colours in either method can involve irradiation and annealing. Disclosed treatment is a marker of transparency, not a flaw. The only red flag is undisclosed treatment.

Can You Tell the Difference Between CVD and HPHT?

No. Not with the naked eye and not with a basic diamond tester. Both pass a diamond tester because both are diamond. Only specialised gemological equipment, such as GIA's DiamondView imaging and photoluminescence spectroscopy, can identify the growth method by reading internal growth patterns, strain and fluorescence. This is precisely why the growth method appears on the certificate rather than being something a buyer could detect themselves.

Certification: What IGI and GIA Reveal

Both IGI and GIA grade lab grown diamonds and disclose the growth method and any post-growth treatment in the comments section of the report, plus a laser inscription on the girdle identifying the stone as laboratory-grown. IGI is the dominant grader of lab grown diamonds worldwide.

An important development took effect from October 2025. Per GIA's announcement on 26 August 2025, GIA moved away from the traditional D-to-Z colour and FL-to-I3 clarity scales for lab grown diamonds, instead issuing a two-tier "Premium" or "Standard" quality assessment. GIA President and CEO Pritesh Patel stated: "Using descriptive terms for the quality of laboratory-grown diamonds is appropriate as most fall into a very narrow range of colour and clarity. Because of that, GIA will no longer use the nomenclature created for natural diamonds to describe what is a manufactured product". GIA notes that more than 95 per cent of lab grown diamonds fall into this narrow band. The fee is US$15 per carat and the minimum submission size is 0.15 carats.

IGI, by contrast, continues to issue the full, detailed 4Cs reports for lab grown diamonds. IGI's CFO has stated that "it's of paramount importance that consumers get that sort of in-depth information, rather than just making it extremely simplistic and generic".

LOHR provides independent IGI certification on stones of one carat and above.

Does CVD or HPHT Cost More?

The method has minimal impact on price. Price is driven overwhelmingly by the 4Cs. There can be a small wholesale difference, with CVD often carrying a lower wholesale cost. But at retail, an equivalent-quality stone is priced similarly regardless of method.

Which Should You Choose?

Neither method is inherently better. Quality varies within each. What matters is the individual stone's cut, colour, clarity and carat and an independent IGI or GIA report.

CVD offers wide availability of larger colourless stones. The largest faceted lab-grown diamond to date, the 75.33 carat "Celebration of India", was CVD-grown and IGI-graded, unveiled at JCK Las Vegas in May 2024. HPHT is strong for top D-colour whites and fancy colours. But the decision should be the diamond in front of you, not the acronym.

Conclusion

Both CVD and HPHT lab grown diamonds are real, beautiful and durable. The growing method is a footnote on the certificate, not the main event. Focus on cut and the 4Cs and choose an independently certified stone. Speak with the LOHR team in Brisbane City, or explore LOHR's independently certified, made-to-order lab-grown pieces.

Frequently Asked Questions

Is CVD or HPHT better?

Neither is inherently better. Both produce real diamonds with identical hardness, brilliance and durability and both are graded on the same 4Cs. CVD tends to suit larger colourless stones, while HPHT is favoured for top D-colour whites and fancy colours. The right choice is the individual certified stone, not the method.

Which is more expensive, CVD or HPHT?

The difference is minimal. Price is driven by the 4Cs, not the growth method. An equivalent-quality CVD and HPHT diamond of the same carat and cut will be priced similarly at retail.

Can you tell the difference between CVD and HPHT?

Not with the naked eye and not with a basic diamond tester. Only specialised gemological equipment can identify the growth method by examining internal growth patterns and fluorescence. That’s why the method is stated on the certificate.

Are CVD diamonds real diamonds?

Yes. A CVD lab-grown diamond is chemically, physically and optically identical to a mined diamond. In 2018, the US Federal Trade Commission removed the word "natural" from its definition of a diamond, recognising lab-grown stones as real diamonds.

Is a CVD diamond as good as a natural diamond?

In terms of hardness, brilliance and optical properties, yes. Both are real diamonds and score 10 on the Mohs scale. The difference is origin and price, not quality or beauty.

Do CVD diamonds pass a diamond tester?

Yes. Because a CVD diamond is a real diamond, it passes a standard thermal and electrical diamond tester. A simulant such as cubic zirconia or moissanite would not test the same way.

Does the growth method appear on the certificate?

Yes. Both IGI and GIA disclose whether a diamond is CVD or HPHT in the comments section of the report, along with any post-growth treatment.

Is HPHT treatment bad?

No. HPHT annealing to improve colour is a standard, accepted, permanent and stable process and it is common for CVD stones. It does not weaken the diamond. Reputable labs disclose it. The only concern is undisclosed treatment.

Which method do most jewellers use?

CVD has become the dominant method for gem-quality colourless stones, especially in larger sizes, though HPHT remains widely used for melee and fancy colours. Both are common in fine jewellery today.