Synthetic: HPHT, CVD, and Quality

A synthetic diamond (laboratory-grown) is not a simulant. If the material is crystalline diamond, the question “Is it diamond?” is separate from the question “Where and how did it grow?” (In the United States, the FTC Jewelry Guides, 16 CFR Part 23, also permit the qualifiers laboratory-grown and laboratory-created; jurisdiction: US.)

Essential

The two principal commercial growth technologies are HPHT and CVD.

HPHT creates high-pressure, high-temperature conditions in which carbon is transported toward a seed and crystallizes as new diamond material. CVD uses an activated gas phase at much lower pressure; diamond grows layer by layer on a crystalline substrate.

Both technologies can produce gem-quality material. Neither growth method nor diamond type is, by itself, a quality grade.

Three events must be separated:

growth method, then as-grown state, then any post-growth treatment.

A CVD-grown diamond that is HPHT-treated after growth remains CVD-grown; treatment does not rewrite its growth history.

How to Read This in Practice

Synthetic diamonds can differ in:

• color and clarity;
• growth zones and sectors;
• inclusions;
• strain patterns;
• spectroscopic centers;
• whether they were subsequently treated.

HPHT material often shows sectoral growth architecture, while CVD often shows layered growth and boundaries among growth runs. But no single microscopic characteristic is a universal test.

The same applies to SiV, NV centers, metallic inclusions, magnetism, or a type II finding: they can be important parts of the body of evidence, but professional origin identification is based on a combination of microscopy, luminescence, and spectroscopy.

Screening Is Not Identification

An ordinary diamond tester primarily tries to resolve the material question. That is not the same thing as natural/synthetic origin.

A professional screening system can produce device-defined results such as PASS, REFER, or, where defined, OUT-OF-RANGE. OUT OF SCOPE describes a validated-applicability boundary and is not a synonym for that device result. Each label and boundary must be read according to the documentation of the specific instrument, version, sample configuration, and validated sample type.

REFER does not mean “synthetic.” It means the result requires additional work according to the defined workflow.

Mounted, loose, melee, and rough material are not necessarily the same screening problem. An instrument validated for one sample type should not automatically be extended to all others.

Quality and Report

Synthetic origin is not a quality grade. Weight, color, clarity, and geometry remain real properties of the stone, but laboratories do not have to use exactly the same report model or the same categories.

An informal conversion between different institutional systems should therefore not be invented. A report is always read according to:

1. the laboratory;
2. the service type;
3. the date;
4. the scope of the specific document.

A laser inscription and report number help, but they do not replace physical matching of the stone to the document.

Practical Framework: Separate Growth Method, Post-Growth Treatment, and Quality

A synthetic diamond is diamond material. The key distinction from natural diamond is growth history, not basic material identity. HPHT and CVD should therefore first be understood as two growth architectures, and only then should we consider the defects, inclusions, or luminescence patterns they may leave.

HPHT growth uses very high pressures and temperatures and a metallic solvent-catalyst; the crystal can show sectoral growth and differing distributions of nitrogen, boron, or metallic remnants. CVD grows from an activated gas phase on a seed at much lower pressure, often with layered architecture and multiple growth runs. No “typical” sign is universal: a metallic inclusion or magnetism is not a stand-alone HPHT test, just as SiV, type IIa, or a particular color is not a stand-alone CVD test.

Take particular care to preserve the distinction between HPHT growth and HPHT treatment. A CVD-grown stone can be HPHT-treated after growth and remains CVD-grown. Irradiation, annealing, or other post-growth processes can further modify optical centers without erasing the entire growth architecture.

Quality is a separate axis. Carat, color, clarity, and geometry are real properties of synthetic stones as well, but laboratories do not have to use the same report model. Beginning October 1, 2025, GIA changed part of its D–Z synthetic service to a Premium/Standard model, while other institutions may retain different nomenclature. Do not create an informal crosswalk among different systems.

When to Escalate

Escalate when basic screening or a microscopic sign does not resolve natural/synthetic origin, growth method, or treatment status. For treatments, also escalate before thermal or chemical servicing if stability and disclosure are unknown.

Quick Check Before Reaching a Conclusion

Before accepting a technical, purchasing, or documentary conclusion, run this short check:

• Have I first confirmed that the material is diamond, and then addressed origin?
• Am I distinguishing HPHT growth from HPHT post-growth treatment?
• Am I avoiding the use of a metallic inclusion, magnetism, SiV, or type IIa as a stand-alone origin test?
• Is the growth architecture connected with spectroscopic and luminescence findings?
• Am I reading the quality report according to laboratory, service, and date without an invented crosswalk?

Common Mistakes

“Synthetic is the same as cubic zirconia.”
No. CZ is a simulant; a synthetic diamond is diamond material of a different origin.

“HPHT always means treatment.”
No. HPHT can refer to a growth method or to a separate post-growth treatment; context is decisive.

“Type IIa means CVD.”
No. Diamond type is not a final growth-origin test.

“REFER on a screener means the stone is synthetic.”
No. It is a triage result, not a final diagnosis.

Remember

With a synthetic diamond, read at least five separate axes: material, origin, growth method, treatment status, and quality. Only after that come market value and other commercial claims.

Go Deeper in The Book

• Chapters 48–54 — synthetic definition, HPHT, CVD, growth features, post-growth treatments, screening, and grading