How Gemological Laboratories Identify Lab-Grown Diamonds

Standard gemological testing equipment—such as refractometers, specific gravity liquids, thermal conductivity pens, and optical microscopes—cannot distinguish a lab-grown diamond from a natural diamond. Because both materials are 100% crystallized carbon with identical hardness, refractive index, and density, traditional testing methods yield identical positive diamond readings.

To solve this, major gemological laboratories (such as IGI, GIA, and De Beers Technologies) developed sophisticated spectroscopic instruments that analyze atomic-level structural defects and growth sector geometry.

Fourier Transform Infrared (FTIR) Spectroscopy is the primary first-line analytical tool in gemological laboratories. FTIR passes an infrared beam through the diamond and measures absorption bands caused by atomic lattice vibrations:

• Natural Diamonds (98%): Display pronounced infrared absorption bands in the 1000–1400 cm⁻¹ region caused by aggregated nitrogen pairs (A-centers) and nitrogen clusters (B-centers). These are classified as Type Ia diamonds.
• Lab-Grown Diamonds (98%+): Exhibit virtually zero absorption in the 1000–1400 cm⁻¹ range because their nitrogen impurity concentration is below 1 ppm. These are classified as Type IIa diamonds.

While finding a Type IIa diamond does not instantly prove lab origin (since ~1.8% of mined diamonds are natural Type IIa stones), it serves as a critical screening checkpoint requiring secondary spectroscopic verification.

Developed by the Diamond Trading Company (DTC/De Beers), the DiamondView instrument illuminates diamonds with deep ultraviolet radiation at wavelengths shorter than 225 nanometers. Because this energy is absorbed in the uppermost surface layer of the diamond, it reveals the structural growth patterns of the crystal:

• Natural Diamonds: Display blue or green octahedral growth zoning patterns with concentric triangular growth bands (macles).
• CVD Lab Diamonds: Display planar, layer-by-layer step growth patterns with characteristic reddish-orange or green fluorescence and distinctive striation bands.
• HPHT Lab Diamonds: Display geometric cuboctahedral growth sectors (hourglass or Maltese cross patterns) with intense green, yellow-green, or turquoise-blue fluorescence and strong phosphorescence (afterglow).

Photoluminescence (PL) Spectroscopy is the definitive scientific court of appeal in diamond verification. The diamond is immersed in liquid nitrogen at cryogenic temperatures (-196°C / 77 Kelvin) and excited by high-intensity lasers (typically 532 nm, 473 nm, or 830 nm):

• Silicon-Vacancy Defect (SiV⁻ / SiV⁰): A diagnostic doublet peak at 737 nm indicates the presence of silicon atoms incorporated from quartz reactor windows during CVD plasma growth.
• Nickel / Cobalt Complexes: Strong optical emission lines at 882 nm, 883 nm, and 884 nm identify nickel-related catalyst defects exclusive to HPHT synthesis.
• Nitrogen-Vacancy Centers (NV⁻ at 637 nm & NV⁰ at 575 nm): The ratio of charged to neutral nitrogen-vacancy states confirms whether the stone underwent post-growth annealing.

For B2B wholesale operations handling hundreds of carats of loose melee daily, running every individual 1.00 mm stone through an FTIR spectrometer is impractical. The industry relies on automated screening devices certified by the ASSURE Program:

• DiamondSure: High-speed optical absorption tester that screens single stones in seconds, sorting them as "Pass" (natural Type Ia) or "Refer" (Type IIa / Lab-Grown).
• AMS2 (Automated Melee Screener): Robotic hopper that automatically dispenses, measures, and tests up to 3,600 small round melee diamonds per hour (0.80 mm to 2.80 mm), separating lab stones with a 0% false pass rate.
• SYNTHdetect: Tabletop imaging device that screens large batches of mounted jewelry and loose parcels simultaneously using luminescence time-resolved imaging.