Is my diamond real? What a photo can and cannot show

Diamond identification rests on measured physical properties: refractive index (2.417), dispersion (0.044), specific gravity (3.52), and its cubic crystal system with single refraction. None of those can be measured from a photograph. A camera records colour, shape and the pattern of light leaving facets — not how light bends inside the stone.

The classic home tests are weaker than they look. A "dot test" can be defeated by a moissanite or a well-cut simulant; the "fog test" reflects how quickly a stone conducts heat, which any hand-warm stone passes; scratch tests damage both the stone and the tester's credibility. Reading a stone by eye is what trained jewellers do, and even they confirm with instruments.

High-refractive-index simulants are the reason. Cubic zirconia (RI 2.15–2.18) and moissanite (RI about 2.65–2.69) both return light in a way that photographs look convincing, especially under jewellery-store lighting.

A sharp, evenly lit photograph is still useful, because some cues are visible: the cut outline and facet proportions, colour zoning inside the stone, surface wear or abrasion, an inscription on the girdle if it is legible, and hallmark stamps on the metal setting.

Optical character can also hint at a direction. Moissanite has unusually high dispersion (0.104 versus diamond's 0.044), so it throws noticeably more spectral "fire"; at high magnification it also shows facet doubling because it is doubly refractive while diamond is not. Those are indicators to investigate — not proof, and not reliable from a soft or heavily compressed image.

A jeweller or gemmologist uses instruments: a refractometer for refractive index, a polariscope to test single versus double refraction, a dichroscope, a spectroscope, a microscope for inclusions, and a thermal or electrical tester that separates diamond from most simulants in seconds. Specific gravity is measured hydrostatically. Diamond testers are quick but can be fooled by a coated stone or confused by a mounted setting.

Treatments and origin sit beyond all of these instruments in most cases. Detecting fracture filling, laser drilling, HPHT treatment or a lab-grown origin generally needs laboratory methods such as FTIR and Raman spectroscopy. That is why a report from a laboratory like GIA, IGI or AGL carries weight, and a photograph does not.

A photo-based screening can organise what is visible and suggest which species the stone most closely resembles, along with the reference values that belong to that species. It is a starting point for a conversation with a jeweller, an aid when sorting a tray of estate finds, and a way to decide whether a stone is worth an appraisal.

It cannot authenticate, grade, value definitively, or detect treatments. Any tool claiming otherwise is overstating what a photograph contains. If the answer matters — a purchase, a sale, an insurance schedule — the stone goes to a laboratory.