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Learn · Lesson 18

Laboratory-Grown: HPHT, CVD, and Quality

HOK-DIA-LESSON-00018Time-sensitive

Learning Objectives

Core

The two principal commercial growth technologies are HPHT and CVD.

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

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

Keep three events separate:

growth method → as-grown state → possible post-growth treatment.

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

Apply

A laboratory-grown diamond is diamond material. The central difference from natural diamond is growth history, not basic material identity. HPHT and CVD should therefore be understood first as two growth architectures and only then through the defects, inclusions, or luminescence patterns they may leave behind.

HPHT growth uses very high pressures and temperatures and a metallic solvent-catalyst. A crystal may show sectoral growth and different distributions of nitrogen, boron, or metallic remnants. CVD grows from an activated gas phase on a seed at much lower pressure, often through layered growth and multiple growth runs. No “typical” feature 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.

Preserve the distinction between HPHT growth and HPHT treatment. A CVD-grown stone can be HPHT-treated after growth and still remains CVD-grown. Irradiation, annealing, or other post-growth treatments can further alter optical centers without erasing the underlying growth architecture.

Quality is a separate axis. Carat, color, clarity, and geometry are real properties of laboratory-grown diamonds, but laboratories do not necessarily use the same reporting model. Since October 1, 2025, GIA has used a Premium/Standard architecture for the relevant laboratory-grown D–Z service rather than the older grading model, while other institutions may use different nomenclature. Do not invent an informal one-to-one crosswalk between those systems.

Check Your Understanding

Conclusion Boundary

Escalate when basic screening or a microscopic feature does not resolve natural/laboratory-grown origin, growth method, or treatment status. For treated material, also escalate before thermal or chemical service when stability or disclosure is uncertain.

Common Mistakes

“Laboratory-grown is the same thing as cubic zirconia.”
No. CZ is a simulant; laboratory-grown diamond is diamond material with a different growth origin.

“HPHT always means treatment.”
No. HPHT can describe a growth method or a separate post-growth treatment; context is essential.

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

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

Remember

For a laboratory-grown diamond, read at least five separate axes: material, origin, growth method, treatment status, and quality. Market value and other commercial claims come only after those are separated.

Sources

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