A laboratory-grown diamond is real diamond, made in weeks instead of billions of years. There are two ways to make one. Step through both machines, see the crystal each one produces, and how a gem laboratory still tells them apart from a natural stone.
There are no reliable visual clues: a lab-grown diamond has the same hardness, refractive index and sparkle as a natural one, and a loupe cannot separate them. Laboratories look at how the crystal grew, under deep ultraviolet light (the DiamondView instrument) and with spectroscopy.
Illustrations of the typical patterns described by GIA, not photographs. Real stones vary, and treated stones can show mixed features.
| Feature | Natural | HPHT-grown | CVD-grown |
|---|---|---|---|
| Growth pattern (DiamondView) | Concentric growth, networks of dislocations | Cross-shaped pattern from cube and octahedron growth sectors | Fine parallel striations, often seen through the pavilion; bands where growth stopped and restarted |
| Diamond type | Mostly type Ia (contains nitrogen) | Type IIa or IIb (boron, blue) | Type IIa (no detectable nitrogen) |
| Fluorescence (long-wave UV) | When present, almost always blue | Often inert in long-wave; may phosphoresce after short-wave UV | Near-colourless: mostly none; when present orange, green or yellow, rare in natural diamond. Pink: orange to red |
| Inclusions | Minerals, crystals, twinning wisps | Dark metallic flux inclusions (can make a stone attracted to a magnet) | Black graphite pinpoints and clouds |
| Strain (crossed polarisers) | Common, patchy | Extremely low | Banded, low-order strain |
| Spectroscopy | N3 centre (nitrogen) | Nickel-related centres possible | Silicon-vacancy centre at 736.6/736.9 nm, very rare in natural diamond |
| After growth | May be treated (HPHT, irradiation) | Colours such as pink and red by irradiation and heating | Most colourless CVD was brown and decolourised by HPHT annealing |
For the trade: every diamond in a parcel can be screened with a desk-top device, and anything referred goes to a laboratory. A GIA report for a lab-grown stone says so on the report itself.
Lab-grown ruby, sapphire, emerald, spinel and alexandrite have been made for more than a century. Four methods cover almost all of them, and each leaves its own clue under the microscope.
Accepted in the US (FTC Jewelry Guides, 2018)
Not acceptable
J. E. Shigley, HPHT and CVD diamond growth processes, GIA, 2016 (temperatures, pressure, solvents, growth times, crystal shapes, post-growth HPHT annealing).
S. Eaton-Magaña and J. E. Shigley, Observations on CVD-grown synthetic diamonds: a review, Gems & Gemology, Fall 2016 (type, DiamondView striations, SiV centre, fluorescence statistics, graphite inclusions, strain).
GIA, Identifying lab-grown diamonds (DiamondView patterns: concentric natural, cross-shaped HPHT, striated CVD; metallic inclusions in HPHT).
GIA, An introduction to synthetic gem materials; Sapphire series part 4; Gems & Gemology Summer 2024, Laboratory growth of gem materials (flame fusion, Czochralski, flux and hydrothermal growth and their inclusions).
US Federal Trade Commission, Guides for the Jewelry, Precious Metals, and Pewter Industries, revised 2018 (16 CFR Part 23; naming of laboratory-grown diamonds); summary in National Jeweler, 8 key changes the FTC made to the Jewelry Guides.
Diagrams are simplified illustrations, not engineering drawings. No prices: JewelLoop does not compare or value stones.