A lab report is the formal written statement of opinion issued by a gemmological laboratory describing a gemstone's identity, treatment status, key gemmological measurements and, in the case of fine coloured stones, often a country-of-origin opinion. The term is used interchangeably with grading report, certificate and grading document, although certification is the most common consumer-facing word.

What a lab report contains

For a faceted diamond, the report typically contains the report number, date of issue, shape and cutting style, measurements, weight, colour grade, clarity grade with a plotted clarity diagram, cut grade, polish, symmetry, fluorescence, and any inscription on the girdle. Comments may note treatments, the proportions of the stone, and any noteworthy features. For a coloured stone the report contains identity (species and variety), measurements, weight, colour description, optional cutting grade, treatment status with detailed indication of detected treatments, and country of origin where the laboratory issues such opinions. For pearls, the report addresses natural versus cultured origin, type of pearl, dimensions, colour, lustre, surface, shape and any treatments.

Premium reports include photographs of the stone, plotted inclusion diagrams, detailed treatment commentary and origin discussion. Mini-reports or short certificates omit some of the descriptive content and serve principally as authentication.

Issuing laboratories

The major laboratories issuing reports recognised in international trade include GIA, SSEF, Gubelin Gem Lab, AGL, GIT, Lotus Gemology, GCAL, IGI, HRD, AnchorCert, BGI and others. Each has its own grading standards, masterstone collection, instrumentation and origin-determination methodology. The trade understands that not all reports are equivalent: the entries on lab arbitrage, lab divergence discount and certificate premium discuss the resulting price stratification by issuer.

Validity and verification

A lab report is a statement of opinion at the time of examination. It does not warrant future condition; a stone subsequently damaged, recut, or further treated may no longer match the report. Most major laboratories provide online verification, allowing the report number to be entered on the laboratory's website to confirm that the report is genuine and matches the issuer's records. The trade routinely verifies reports of significant value before transaction; sophisticated buyers will accept only reports that can be electronically verified.

Disputes and re-issue

Where the receiving party disagrees with a grade or determination, the stone may be re-submitted to the same or a different laboratory. The first laboratory will not normally amend a report based on disagreement; only on documented error or new physical examination of the same stone will an amendment issue.