CVD vs HPHT Lab-Grown Diamonds

The characteristics in this table are possible tendencies, not a checklist for judging every diamond. Production methods continue to improve, and modern stones may not display the features historically associated with their growth process.

CVD stands for chemical vapour deposition. During the CVD process, a thin piece of previously grown diamond is placed inside a chamber. The chamber is filled with carbon-containing gas and energy is applied to create a plasma.

The energy separates carbon atoms from the gas molecules. These carbon atoms settle onto the diamond seed and gradually form additional diamond crystal.

Unlike HPHT growth, CVD does not require the same extremely high pressure. The diamond normally grows as a relatively flat or tabular piece of rough material.

The simplified process is:

1. A thin diamond seed is cleaned and placed inside a growth chamber.
2. Carbon-containing gas is introduced.
3. Energy converts the gas into plasma.
4. Carbon atoms separate from the gas molecules.
5. Carbon accumulates on the seed in layers.
6. The rough diamond is removed, assessed, cut and polished.

The technical environment must be carefully controlled. Changes in gas composition, temperature or growth stability can influence colour, internal features and the quality of the resulting crystal.

Learn more about both production methods in our guide to how lab-grown diamonds are made.

HPHT stands for high pressure high temperature.

The process places a diamond seed, a carbon source and metallic material inside a specialised growth capsule. The capsule is subjected to very high temperature and pressure.

The metal melts and helps dissolve the carbon. Carbon then moves towards the cooler diamond seed, where it crystallises and enlarges the diamond.

GIA describes HPHT growth as taking place at approximately 1,300–1,600°C and pressures of around 5–6 GPa. GIA’s explanation of HPHT growth provides further technical detail.

The simplified process is:

1. A diamond seed is placed inside a growth capsule.
2. A carbon source and metallic flux are added.
3. The capsule is placed inside a powerful press.
4. Extreme pressure and heat dissolve the carbon.
5. Carbon crystallises around the seed.
6. The rough crystal is removed, cut and polished.

HPHT conditions are designed to reproduce some of the extreme environmental factors involved in natural diamond formation, although the laboratory process is controlled and considerably faster.

The biggest difference is the environment in which the diamond crystal grows.

HPHT relies on extreme pressure, extreme temperature and a molten metallic medium. CVD relies on carbon-containing gas, plasma and substantially lower pressure.

These different environments influence the shape of the rough crystal and may produce different microscopic growth features. They do not change the fundamental fact that both resulting materials are diamonds.

For shoppers, this distinction is mostly about origin and production—not a visible difference between two well-cut finished diamonds.

Normally, not to the unaided eye.

Two polished diamonds with comparable cut, colour, clarity, carat weight and proportions may appear virtually identical even when one was produced by CVD and the other by HPHT.

The growth process can leave microscopic or spectroscopic features, including:

• Different crystal-growth patterns
• Different fluorescence or phosphorescence behaviour
• Metallic inclusions in some HPHT-grown diamonds
• Dark graphitic inclusions in some CVD-grown diamonds
• Colour zoning or strain patterns
• Features connected with post-growth treatment

These characteristics are used by trained gemmologists as part of professional identification. However, they are not reliable DIY tests for consumers.

GIA notes that HPHT-grown diamonds can contain metallic flux inclusions, while CVD-grown diamonds may contain dark graphitic or other mineral inclusions. Such features may provide clues, but they are not present in every stone and are not always conclusive. GIA explains these growth-related features.

Trained laboratory gemmologists use professional tools to identify CVD or HPHT growth characteristics.

Neither process guarantees better quality. High-quality and lower-quality diamonds can be produced through either method. The final result depends on factors such as:

• The quality and orientation of the diamond seed
• Stability during growth
• Control of temperature and pressure
• Gas purity in CVD production
• The metallic growth environment in HPHT production
• Interruptions during growth
• Post-growth processing
• Cutting and polishing quality

The most important consumer-facing quality factors remain the characteristics of the individual diamond. A beautifully cut CVD diamond may outperform a poorly cut HPHT diamond. A beautifully cut HPHT diamond may outperform a poorly cut CVD diamond. The method should therefore be treated as one piece of product information, not as an overall quality grade.

Both processes can produce colourless, near-colourless and coloured laboratory-grown diamonds.

Historically, some CVD-grown material displayed brownish colour associated with crystal defects. Some of these diamonds were subsequently treated under HPHT conditions to reduce or modify that colour. HPHT growth can also produce colour effects depending on trace elements and conditions inside the growth chamber. Improvements in manufacturing have enabled both processes to create high-colour-grade material.

Recent GIA research shows how significantly production has developed. Its laboratory has received large, colourless examples produced through both methods, demonstrating that older assumptions about one process always producing a particular colour are no longer dependable. GIA’s laboratory-grown diamond update documents these continuing changes.

Instead of assuming one process has better colour, check the colour information on the diamond’s grading report and evaluate how the stone looks in neutral lighting.

Both CVD and HPHT diamonds can receive high clarity grades. Both can also contain inclusions or growth features.

Some HPHT-grown diamonds may contain metallic flux inclusions originating from the growth environment. Some CVD-grown diamonds may contain dark graphitic inclusions, pinpoints or features related to interruptions between growth stages.

The presence of an inclusion does not automatically make a diamond unsuitable for jewellery. Its importance depends on size, number, position, relief and visibility, effect on transparency, effect on durability, and whether it can be seen without magnification.

Consumers should focus on the actual clarity assessment and visual appearance of the finished diamond rather than assuming all CVD or all HPHT stones share the same inclusions.

The growth method does not directly determine how much a finished diamond sparkles.

Brilliance, fire and scintillation depend primarily on cut quality, including proportions, facet angles, symmetry, polish, light performance, and the shape and cutting style.

If an HPHT and CVD diamond have comparable optical properties and equally strong cutting, neither should receive an automatic advantage because of its production method. When choosing jewellery, inspect high-resolution images, videos and available grading information. The quality of the cut generally provides more useful information about sparkle than the letters CVD or HPHT.

A diamond's brilliance is governed by its cut and symmetry, regardless of CVD or HPHT growth origins.

An HPHT-treated CVD diamond was originally grown through chemical vapour deposition and was later exposed to high pressure and high temperature. This does not mean that the diamond was grown twice or that it became an HPHT-grown diamond. Its growth origin remains CVD.

The later HPHT process is a treatment, generally used to modify characteristics such as colour. GIA explains that post-growth HPHT treatment does not add more diamond material to the crystal; it is different from HPHT growth. GIA’s research on post-growth treatment clarifies this distinction.

Therefore: CVD-grown describes how the diamond crystal was created, while HPHT-treated describes a process applied after the crystal had grown.

Independent reports may indicate the growth method and whether the laboratory detected evidence of post-growth treatment.

Post-growth treatment is not automatically evidence of a poor diamond. Treatments can be part of modern laboratory-grown diamond production. The important issue for buyers is transparency: relevant treatment information should be disclosed accurately and should agree with the grading report.

IGI states that its laboratory-grown diamond reports can identify the growth process and indicate whether a stone is “as grown” with no indication of post-growth treatment or may include treatment. IGI’s reporting explanation describes how this information is presented.

Not reliably through an ordinary visual inspection. Certain inclusions or growth features can suggest a possible method, but advanced laboratory testing may be necessary for a conclusive identification. Professional laboratories use combinations of spectroscopy, fluorescence imaging, photoluminescence analysis, infrared analysis, magnification, and other specialised screening instruments.

Consumers should not rely on at-home tests, photographs, sparkle or colour to determine whether a diamond is CVD- or HPHT-grown. A recognised laboratory report is considerably more dependable.

There is no universal price rule. A CVD diamond may cost more or less than an HPHT diamond depending on carat weight, cut quality, colour, clarity, shape, production cost, post-growth processing, availability, supplier/retailer pricing, and precious-metal content.

Market prices and production technologies change over time. A statement that CVD is always cheaper—or that HPHT is always more expensive—can quickly become inaccurate. Compare complete specifications and the finished jewellery price rather than using the growth process as the only pricing indicator.

The growth method alone is not enough to establish environmental performance. CVD and HPHT both require energy, equipment and manufacturing infrastructure. Their environmental impact can vary according to the electricity source, reactor or press efficiency, length of the production run, success rate, factory location, material inputs, and renewable-energy use.

It would therefore be misleading to claim that every CVD diamond is environmentally superior to every HPHT diamond. Buyers interested in environmental performance should look for specific, verifiable information about the producer and its energy sources instead of relying only on the growth-method label.

Many laboratory-grown diamond reports identify the growth method. The exact terminology and information provided depend on the issuing laboratory and its current reporting policy.

Read our guide to what lab-grown diamonds are for a broader introduction to their properties and classification.

Either can be suitable for fine jewellery. For a jewellery buyer, a sensible order of evaluation is:

• Confirm that the stone is clearly disclosed as laboratory-grown.
• Check the independent grading information.
• Evaluate cut, colour, clarity and carat weight.
• Examine high-quality photographs or videos.
• Check whether any visible inclusions affect appearance.
• Confirm the growth method and treatment information.
• Assess the jewellery setting and metal.
• Review warranty, shipping and returns.
• Compare the total price with equivalent pieces.

The growth method can be considered after the features that determine the diamond’s actual appearance and suitability.

Choose the better individual diamond, not simply the preferred acronym.

A strong candidate should have a cut that produces attractive light performance, colour that suits the jewellery design and metal, clarity that appears clean at normal viewing distance, independently documented specifications, clear laboratory-grown disclosure, transparent growth/treatment info, a secure setting, and a price appropriate for the complete piece.

If two diamonds appear equally attractive and have comparable specifications, choosing either CVD or HPHT can be reasonable. The best option is the one whose documented quality, appearance and price suit your requirements.

In UK-facing content, Aurelia should consistently use a clear qualifier such as “laboratory-grown” or “lab-grown” with the word diamond. Current UK advertising decisions emphasise that manufactured diamond origin should not be ambiguous. The UK ASA’s diamond terminology ruling provides relevant guidance.

Verify the independent report and check legal white gold white or platinum stamps before ordering.