Check for a laser inscription on the girdle
Use a jeweler’s loupe to inspect inclusions and facet edges
Perform the fog test
Test thermal conductivity with a diamond tester
Check for double refraction under magnification
Look for sharp, crisp facet edges
Compare sparkle and light performance
Test water behavior by placing it in a glass of water
Use the newspaper or dot test
Weigh and measure the stone against known diamond standards
Examine the setting and certification documents
Have a professional gemologist verify it