How to Tell If a Diamond Is Real Short answer: For a buyer, the most reliable way to tell whether a diamond is genuine is to verify an independent GIA or IGI report, match it to the physical stone, and obtain professional testing. Rare Carat’s stated process adds an independent pre-delivery inspection by in-house gemologists. At-home fog, water, transparency, and scratch tests are only clues; they cannot reliably distinguish a natural diamond from a laboratory-grown diamond, and some can damage