Interactive 60fps gemological inspection studio. Because CVD and HPHT lab-grown diamonds pass standard thermal tester pens, use Cross-Polarized Tatami Strain, Shortwave 254nm UV Phosphorescence, and 10x Facet Doubling to separate every stone.
Direct Answer: Standard handheld thermal diamond testers cannot tell the difference between a $10,000 natural mined diamond and a $600 CVD or HPHT lab-grown diamond because both are pure crystallized carbon with identical thermal conductivity. To separate them non-destructively, gemologists inspect Cross-Polarized Strain Patterns, Shortwave UV (254nm) Phosphorescence Afterglow, Metallic Flux Inclusions, and Facet Doubling.
| Diagnostic Property | Natural Diamond (Type Ia) | CVD Lab-Grown (Type IIa) | HPHT Lab-Grown (Type IIb/IIa) | Synthetic Moissanite (SiC) |
|---|---|---|---|---|
| Chemical Formula | Pure Carbon ($C$) + N aggregates | Pure Carbon ($C$) β Layered gas | Pure Carbon ($C$) + Fe/Ni/Co flux | Silicon Carbide ($SiC$) |
| Refractive Index & Doubling | $n = 2.417$ (Single β No doubling) | $n = 2.417$ (Single β No doubling) | $n = 2.417$ (Single β No doubling) | $n = 2.65 - 2.69$ (Doubled facets!) |
| Cross-Polarized Strain (CPF) | Tatami cross-hatch rainbow strain | Parallel banded columnar strain | No strain (Dark isotropic field) | Strong uniaxial optic figure |
| Shortwave UV (254nm) Afterglow | None (Inert after lamp turns off) | Weak orange/red or green glow | Strong chalky blue afterglow (10s+) | Inert or faint orange |
| Cheap Thermal Diamond Pen | Beeps "Diamond" | Beeps "Diamond" (False Pass) | Beeps "Diamond" (False Pass) | Beeps "Diamond" (unless electrical test) |