Look for a diamond certification from a reputable lab (GIA, AGS, IGI) and verify the report number with the lab
Use a loupe (10x) to check for natural inclusions, growth lines, and irregularities
Check the stone’s edges for symmetry and natural wear patterns in mounting settings
Perform the fog test: breathe on the diamond; real diamonds disperse heat and fog clears quickly
Use the heat-conductivity test (diamond tester): real diamonds typically read as true diamond on a verified tester
Check for fluorescence under UV light: some diamonds glow blue (not definitive)
Use a loupe to inspect for “laser inscriptions” or specific markings on natural stones (varies by lab)
Examine the girdle and facets for consistent, realistic facet alignment and natural proportions
Use the “water test” (not definitive): real diamonds usually show strong sparkle compared with glass or cubic zirconia
Check with a refractometer: measure refractive index (diamond is ~2.42)
Use a microscope to look for double refraction: diamond shows single refraction; many substitutes show double refraction
Try the scratch test on an unimportant area: diamond scratches glass easily (only if you’re trained to avoid damage)
Check hardness: diamond is the hardest natural material; substitutes will scratch more easily
Use a jeweler’s testing method (thermal/electrical conductivity) at a reputable shop for confirmation
Avoid relying on single tests like “sparkle,” “fog,” or “UV glow” alone—use multiple checks or certification