Introduction
Identifying a lab-grown diamond is not a single test. It is a workflow — a structured sequence of observations and measurements that begins with a broad filter and narrows progressively toward a definitive conclusion. Each step either confirms the diamond as natural or flags it for the next level of investigation.
This workflow is used by gemological laboratories, diamond grading facilities, and increasingly by retail jewellers and dealers who want to verify the origin of stones in their inventory. The full sequence ranges from a few seconds (automated desk screening) to several minutes (advanced spectroscopy and imaging).
Step 1: Diamond Type Testing
The First Filter
The most efficient initial screen is diamond type determination using FTIR (Fourier Transform Infrared) spectroscopy. This technique measures the nitrogen content and configuration within the crystal lattice — information that reveals how the diamond formed.
Type Ia diamonds contain nitrogen atoms that have aggregated into pairs (IaA) or larger clusters (IaB) over geological time. Approximately 95–98 % of natural gem-quality diamonds are Type Ia. Lab-grown diamonds are virtually never Type Ia because their short growth times do not allow nitrogen aggregation.
Type IIa diamonds contain no measurable nitrogen. They are the purest form of carbon crystal. Only 1–2 % of natural diamonds are Type IIa, but most lab-grown diamonds — both CVD and HPHT (grown in nitrogen-free environments) — fall into this category.
Type IIb diamonds contain boron instead of nitrogen. They are extremely rare in nature (the famous Hope Diamond is one). Boron-doped HPHT diamonds are Type IIb.
Decision point: If a diamond is Type Ia, it is almost certainly natural. The process stops. If it is Type IIa or IIb, it proceeds to Step 2. This single test eliminates the vast majority of natural diamonds from further investigation.
Step 2: UV Fluorescence and Phosphorescence
Diamonds that pass the type filter as Type II are examined under ultraviolet light — both long-wave UV (LWUV, 365 nm) and short-wave UV (SWUV, 254 nm).
Key diagnostic observations:
- Phosphorescence — a lingering glow after the UV source is removed. This is common in HPHT-grown diamonds and very rare in natural diamonds (except natural Type IIb, which is itself extremely rare). Phosphorescence lasting several seconds or more is a strong indicator of HPHT origin.
- SWUV vs LWUV response — many lab-grown diamonds fluoresce more strongly under short-wave UV than long-wave UV, which is the opposite of typical natural diamond behaviour.
- Fluorescence colour — CVD diamonds may show orange or green fluorescence rather than the blue that dominates in natural diamonds.
See UV Fluorescence & Phosphorescence for full detail.
Step 3: Cross-Polarized Filters and Microscopy
If UV testing raises suspicion but does not provide definitive results, the stone is examined under cross-polarized light and standard microscopy.
Cross-polarized light reveals internal strain patterns. Natural diamonds that have spent billions of years in the mantle under tectonic stress show characteristic "tatami" or cross-hatch strain patterns from plastic deformation. Lab-grown diamonds typically show no strain (CVD) or different strain patterns (HPHT). See Cross-Polarized Filters.
Microscopy may reveal:
- Metallic flux inclusions in HPHT diamonds
- Growth striations in CVD diamonds
- The absence of natural mineral inclusions (garnet, olivine, chromite)
Step 4: Spectroscopy
For stones where the evidence is still inconclusive — or to confirm preliminary findings — advanced spectroscopy provides growth-method-specific defect signatures.
Photoluminescence (PL) spectroscopy detects specific defect centres:
- SiV⁻ at 736 nm — diagnostic for CVD origin (silicon contamination from the chamber)
- Ni-related defects at 882/884 nm — diagnostic for HPHT origin
- N3 centre at 415 nm — indicates natural nitrogen aggregation over geological time
UV-Vis absorption spectroscopy maps the colour-causing defects and distinguishes between natural and treated colour origins.
Step 5: DiamondView Fluorescence Imaging
The most visually definitive identification tool. The DiamondView instrument uses deep UV light (below 225 nm) to excite fluorescence from the diamond's internal growth structure. The resulting image reveals the growth pattern:
- Natural diamonds: Irregular octahedral growth patterns
- HPHT diamonds: Cross-shaped or cuboctahedral growth sector patterns
- CVD diamonds: Parallel banding or striations reflecting layer-by-layer deposition
These patterns are among the most reliable and intuitive identification methods available. See Fluorescence Imaging.
Automated Screening Instruments
The full workflow described above is what gemological laboratories perform. For trade and retail settings, automated instruments compress the process:
GIA iD100 — a desktop probe that screens individual stones (including mounted stones as small as 0.9 mm) and delivers "pass" or "refer" results in approximately 2 seconds. It combines type testing and spectroscopic analysis into a rapid automated workflow.
De Beers AMS2 — an automated batch screener for loose melee diamonds, processing up to 3,600 stones per hour in the 0.003–0.20 ct range. Essential for screening melee parcels before setting.
Yehuda Sherlock Holmes — a portable UV fluorescence and phosphorescence analyser that screens multiple mounted and loose diamonds simultaneously, without requiring a probe. Independently verified through the UL ASSURE Testing Program.
Gemetrix — a range of compact, portable UV screening instruments (PL-Inspector, Jewellery Inspector, Melee Inspector) that use dual-wavelength UV at 254 nm and 365 nm with smartphone integration for result capture and comparison.
These and other diamond screening devices are available from specialist suppliers. See Mounted & Melee Screening for detailed specifications.
Frequently Asked Questions
How long does the full screening workflow take?
Automated desk screening takes 2–5 seconds per stone. The full laboratory workflow — type testing through DiamondView imaging — takes several minutes per stone, depending on how many steps are required.
Can a single test definitively identify a lab-grown diamond?
DiamondView imaging comes closest to a single-test answer because growth patterns are highly distinctive. But best practice combines multiple methods for certainty. Type testing alone eliminates most naturals; spectroscopy confirms growth-method-specific defects.
What does "refer" mean on a screening result?
"Refer" means the stone requires further investigation. It does not mean the diamond is lab-grown — only that it cannot be confirmed as natural by the screening instrument's criteria. Rare natural Type IIa diamonds will also receive "refer" results.
Do all jewellers have screening equipment?
Not yet, but adoption is growing rapidly. The GIA iD100 and similar devices are designed for bench-level use. Major diamond trading centres and responsible retailers increasingly screen all incoming inventory.
Summary
The screening workflow moves from broad to specific: type testing (FTIR) eliminates most naturals as Type Ia, UV analysis flags suspicious fluorescence and phosphorescence behaviour, cross-polarized light and microscopy reveal strain patterns and inclusion types, spectroscopy detects growth-method-specific defect centres, and DiamondView imaging captures the definitive growth patterns. Automated instruments compress this sequence into seconds for trade use. The goal is not a single decisive test but a structured accumulation of evidence that leads to a reliable conclusion.