Diamond Knowledge
How to Tell if a Diamond Is Lab-Grown
How to tell if a diamond is lab-grown or natural: not by eye, but by reading the growth history written inside the crystal. This is the full test-by-test reference — every diagnostic a laboratory uses, compared across natural, CVD-grown and HPHT-grown diamonds.
← Part of the Brilliani Labs Diamond Guide
The quick answer: how are lab-grown diamonds detected?
Lab-grown diamonds are detected by their growth signatures, not their appearance. A natural diamond carries aggregated nitrogen and a sharp 415 nm N3 peak that only geological time can produce. A CVD diamond carries the 737 nm silicon-vacancy doublet and striated, layered growth. An HPHT diamond gives itself away with strong, persistent phosphorescence, cross-shaped growth sectors and sometimes metallic flux inclusions. No single test decides it — a laboratory reads several together.
Natural vs CVD vs HPHT — the full comparison table
Seventeen diagnostics, side by side. Bold entries are the strongest tells for that stone.
| Diagnostic | Natural diamond | Lab-grown — CVD | Lab-grown — HPHT |
|---|---|---|---|
| Diamond type | Mostly Type Ia (aggregated nitrogen); only ~1–2% are Type IIa | Almost exclusively Type IIa (no detectable nitrogen) | Type Ib, IIa or IIb — no aggregated nitrogen |
| Infrared (FTIR) spectrum | Strong peaks at 1014, 1082, 1282 and 1365 cm⁻¹ (aggregated nitrogen, IaAB); 3107 cm⁻¹ C–H; 2856 & 2923 cm⁻¹ | No nitrogen absorption in the 1100–1400 cm⁻¹ range; may show 3123 cm⁻¹ (N-V-H) if treated | No aggregated-nitrogen peaks; boron-related peaks if Type IIb |
| UV-Vis absorption | Sharp 415 nm N3 peak; 452 nm (N2) and 475 nm; broad 385 nm sideband | No 415 nm peak; may show 270 nm (isolated nitrogen), 503 nm (H3), 575/637 nm (NV centres) | No 415 nm peak; variable with impurities |
| Photoluminescence (PL) | 415 nm N3 emission — the natural fingerprint; H3 (503 nm), H4 (496 nm) if treated | 737 nm Si-V doublet — the CVD hallmark; 448 nm broadband; NV centres at 575/637 nm | Variable; NV centres possible; typically no Si-V |
| Raman line width (1332 cm⁻¹) | Broader — typically > 6.0 cm⁻¹ FWHM (geological strain) | Narrower — typically < 6.0 cm⁻¹ | Narrower — typically < 6.0 cm⁻¹ |
| Long-wave UV (365 nm) | Stronger than short-wave; of the 25–35% of stones that fluoresce, ~95% glow blue (N3) | Often inert or weak; orange, green or yellow-green when present; can be zoned or banded | Variable; greenish-blue; a cross-shaped pattern may show on crown or pavilion |
| Short-wave UV (254 nm) | Weaker than long-wave; blue if present | Often stronger than long-wave — inverted from natural; orange to yellow-green | Can be strong; greenish-blue or yellow-green |
| Phosphorescence | Very rare (faint blue in the exceptional natural Type IIb) | Uncommon; weak and under ~3 seconds if present | Strong and diagnostic — greenish-blue or yellow-green afterglow, 3 seconds to over a minute |
| Deep-UV growth pattern | Concentric ring-like growth zoning | Striated / layered / banded, parallel to the growth planes | Cross-shaped / hourglass cuboctahedral growth sectors |
| Cross-polarised strain | Mottled "tatami" — varied, irregular, soft smudges, rainbow oil-slick effects | Strong banded "tatami" — coarse, layered, cross-hatch shadows | Little to none — almost entirely inert |
| Inclusions | Cloud-like inclusions, light crystals, feathers, red pyrope crystals, white crystals | Black graphite inclusions (often along growth planes); point inclusions; often inclusion-free at high clarity | Metallic flux inclusions (Fe, Ni, Co) — rod-shaped, plate-like or irregular; can be magnetic |
| Colour distribution | Uneven, irregular zoning if present; never geometric | Even coloration; may show a brownish as-grown tone | Geometric colour zoning by growth sector (Ib yellow, IIb blue, IIa colourless) |
| Growth structure | Octahedral crystals; trigons on rough surfaces | Cube-like or plate-like; layered deposition | Cuboctahedral crystals — cubic + octahedral faces |
| Magnetic response | Non-magnetic | Non-magnetic | May be attracted to a magnet if it carries large metallic inclusions |
| Automated screening | Passes as natural — no flag | Flagged as CVD from the UV response, fluorescence pattern and spectroscopic signature | Flagged as HPHT from the phosphorescence, growth pattern and UV signature |
| Certificate notation | Natural | "Created by CVD; may include post-growth treatment" | "As Grown — no indication of post-growth treatment; Created by HPHT" |
| Thermal conductivity | High (Type IIa highest) | High (Type IIa) | High (Type IIa/IIb highest) |
Scroll the table sideways to see all three columns.
What does "diamond type" reveal?
Diamond type is the first and cheapest sieve. It classifies a stone by its trace impurities: Type Ia holds aggregated nitrogen, Type Ib isolated nitrogen, Type IIa effectively none, and Type IIb boron. Nitrogen aggregation takes geological time — which is why the overwhelming majority of natural diamonds are Type Ia, while CVD diamonds are almost exclusively Type IIa and HPHT stones are Ib, IIa or IIb. A colourless Type IIa result doesn't prove a stone is lab-grown (about 1–2% of naturals are IIa too) — it simply means "send this one for further testing".
What do FTIR, UV-Vis, photoluminescence and Raman show?
Spectroscopy reads the defects in the lattice like a barcode. Infrared (FTIR) picks up the aggregated-nitrogen peaks of a natural Type Ia at 1014, 1082, 1282 and 1365 cm⁻¹ — peaks a lab-grown stone simply doesn't have. UV-Vis and photoluminescence find the two headline fingerprints: the natural diamond's sharp 415 nm N3 line, and the CVD diamond's 737 nm silicon-vacancy doublet — silicon picked up from the reactor itself. As a supporting indicator, the width of the 1332 cm⁻¹ Raman line tends to be broader in natural stones (strained by aeons underground) than in lab-grown ones.
What do UV fluorescence and phosphorescence reveal?
Under a long-wave UV lamp (365 nm), a quarter to a third of natural diamonds fluoresce — and of those that do, around 95% glow blue, evenly and concentrically. CVD stones are often inert or glow weakly in orange to yellow-green, frequently in zoned patches; HPHT stones lean greenish-blue, sometimes with a tell-tale cross on the crown. Two subtler tells: CVD diamonds often fluoresce more strongly under short-wave UV than long-wave — the inverse of natural behaviour — and when the lamp switches off, an HPHT stone can keep glowing. That afterglow, phosphorescence lasting from 3 seconds to over a minute, is one of the most diagnostic signals in the whole toolkit; see our fluorescence guide for the buying side of the story.
What do growth patterns and strain show?
Deep-ultraviolet surface imaging makes the growth history visible directly: concentric zoning in a natural stone, striated parallel bands in CVD, a cross or hourglass of growth sectors in HPHT. Between crossed polarising filters the strain tells the same story from a different angle — natural stones show irregular mottled "tatami" patterns with rainbow interference colours, CVD shows strong coarse banding, and HPHT shows almost nothing at all, because the crystal grew in equilibrium.
What do inclusions and colour zoning reveal?
Under magnification, what's inside the stone often names its maker. Natural diamonds carry clouds, feathers and mineral crystals — even red pyrope garnets. CVD stones may hold small black graphite inclusions along their growth planes. HPHT stones can trap metallic flux — iron, nickel or cobalt from the growth cell — as rods, plates or irregular blobs. Colour arrangement follows the same logic: natural colour zoning is irregular and never geometric, while HPHT colour zoning follows the growth sectors in strikingly geometric fashion.
Can a magnet or a thermal diamond tester detect lab-grown?
A strong magnet occasionally can — an HPHT stone with large metallic flux inclusions may be faintly attracted, which no natural diamond ever is. A standard thermal "diamond tester", however, cannot: it measures thermal conductivity, which is equally high for natural, CVD and HPHT stones, because they are all genuinely diamond. A thermal tester separates diamond from simulants like cubic zirconia; it says nothing about origin. Telling lab-grown from natural takes the spectroscopic and imaging tests above.
How do automated screening machines work?
Screening instruments used at trade level combine several of these signals — UV response, fluorescence and phosphorescence behaviour, spectroscopic features and growth patterns — and issue a quick verdict: pass as natural, or refer with a CVD or HPHT indication. A referral isn't a condemnation; it means "this stone needs a full laboratory". You can try the same logic yourself in our interactive Diamond Testing simulator.
What does the certificate say?
Disclosure ends up on paper. A natural stone's report simply states natural origin. A lab-grown report identifies the growth method — typically wording such as "Created by CVD; may include post-growth treatment" or "As Grown — no indication of post-growth treatment; Created by HPHT" — and lab-grown stones are usually laser-inscribed as such on the girdle. For how to read the rest of the document, see how to read a diamond grading report.
Run the tests yourself.
Pick a natural, CVD or HPHT diamond and flip through all seven screening tests interactively — see exactly what each instrument sees.
Open Diamond Testing →