The essentials
CVD vs HPHT diamonds: growth method, treatment and what to ask.
Two routes to laboratory-grown diamond. Keep the growth process separate from post-growth treatment and the appearance of the finished stone.
The short answer
- CVD and HPHT are growth methods, not automatic beauty grades.
- HPHT can also describe a post-growth treatment, including for a CVD-grown diamond.
- A missing treatment comment is not enough to claim “untreated”.
In this guide
Two ways to grow diamond
Chemical vapour deposition, or CVD, grows diamond on a substrate through reactions involving carbon-containing gases. High pressure, high temperature, or HPHT, uses a carbon source, a diamond seed and a metal-containing growth environment under high pressure and temperature. Both methods produce laboratory-grown diamond; neither is another name for moissanite.
Those process descriptions tell you how the crystal originated, not whether a particular finished stone will be your preferred choice. Keep the actual measurements, reported qualities and appearance in the comparison. Buying a process acronym without those details leaves the central selection question unanswered.
Technical references: [1]
Growth and post-growth processing are separate
A diamond can be grown by CVD and later undergo HPHT processing to change its colour. That does not make “CVD-grown” and “HPHT-treated” contradictory statements. One describes the growth stage; the other describes a later process. GIA’s research distinguishes these stages when discussing laboratory-grown products.
Ask the seller to separate three statements in writing: laboratory-grown origin, the identified growth method, and any disclosed subsequent treatment. Do not let a growth-method answer stand in for a treatment answer. If you require an as-grown stone, make that an explicit sourcing condition and request documentation that supports it.
| Question | What the answer addresses |
|---|---|
| Is it laboratory-grown? | Origin of the diamond |
| Was it grown by CVD or HPHT? | Crystal-growth process |
| Was there post-growth treatment? | Processing after the crystal grew |
| Does it meet my visual brief? | The appearance and suitability of this finished stone |
Technical references: [1]
A coating is not the same claim as internal processing
Surface coating, growth-related colour and post-growth processing are different descriptions. If your concern is a temporary surface effect, ask that exact question: is any surface coating present, and what supports the answer? Do not replace it with the broader question “is it treated?” and assume that a one-word response covers every mechanism.
Do not extrapolate a blanket permanence or heat-resistance guarantee to all treatments. Request the actual stone’s disclosure and appropriate care or setting guidance. A concern about treatment should be resolved before manufacture, especially if the design will involve workshop heat or other processes.
Select the stone, not the slogan
A useful comparison starts with candidates that meet the same brief. Review their neutral-light appearance, outline and any visible characteristics, then compare documentation and complete quotes. Do not assume that CVD is always superior, that HPHT is always cheaper or that one method automatically proves an environmental claim.
When sending a brief, state whether growth method is a preference or a requirement. If your real requirement is an attractive, documented diamond with no surface coating, say that explicitly. This avoids excluding acceptable candidates for the wrong reason while still keeping the important disclosure condition firm.
- Record the growth method where identified.
- Read the actual treatment comments and reporting limitations.
- Resolve any as-grown or no-coating requirement before ordering.
- Review actual-stone imagery and the complete quotation.
- Do not infer origin from a basic handheld tester.
Technical references: [4]
Common questions
Can a CVD diamond also be HPHT treated?
Yes. Growth and subsequent processing are separate stages. Ask for both disclosures for the actual candidate.
Does HPHT automatically mean poor quality?
No process acronym is a complete quality assessment. Compare the actual finished stone, its report and its appearance.
Does an empty comments field prove there was no treatment?
No. Check the scope and wording of the report and obtain clarification if untreated or as-grown material is a requirement.
Sources & editorial method
Prepared with AI assistance and checked against the primary references linked below. Our comparisons, worked examples and buying checklists are editorial guidance, not independent laboratory tests or a professional appraisal. Actual stone details and order terms require separate confirmation.
- GIA research: laboratory-grown diamond identification and products (2024) (opens in a new tab)
- IGI: growth and post-growth treatment disclosures (opens in a new tab)
- IGI: laboratory-grown diamond reports (opens in a new tab)
- IGI: limitations of handheld diamond testers (opens in a new tab)
Technical sources checked on 5 October 2026. Laboratory services and report formats may change; the current issuing laboratory’s record takes precedence.
Read the wording, not an assumed translation
IGI has published reporting language concerning as-grown stones and possible post-growth treatment. Current service information also explains that growth and treatment details may depend on the requested report. Read the actual comments, report date and service scope; do not assume that every document answers every treatment question.
“No indication” and “may include” are not interchangeable phrases. Nor does an absent comment automatically mean a stone is untreated. Ask the issuing laboratory or the supplier for clarification where the wording does not answer a non-negotiable requirement. Keep that clarification attached to the stone’s identity, not merely to a general collection description.
Technical references: [2], [3]