A diamond sold with a “certificate” usually comes with a grading report from a gemmological laboratory. It is one of the most useful documents in the jewellery trade, and one of the most misread. This guide explains what such a report is, what each part of it records, and what it does not say. It uses the Gemological Institute of America’s reports as the example, because GIA publishes how its own reports work; other laboratories issue reports with similar sections, but their scales and methods are their own. Nothing here ranks one laboratory against another.
A report, not a certificate, and not a valuation
GIA is direct about what its documents are. In its own words, a diamond report “is not a certificate or guarantee and does not indicate a diamond’s monetary value.” It describes the stone’s measurable qualities at the time it was examined. An appraisal is a different document with a different purpose: GIA describes it as an estimate of a diamond’s monetary worth, based on current market conditions and the quality of the diamond. A grading report is often one of the inputs an appraiser uses, but it is not an appraisal and carries no price.
That distinction matters in both directions. A report describes the stone; it does not say what anyone will pay for it, and two stones with identical grades can still differ in ways that matter to a buyer. And a document that does put a figure on a stone is an appraisal, written by an appraiser for a stated purpose such as insurance, and should be read as that.
What the report records
A full grading report sets out the stone’s identity and its grades. The fields, in roughly the order they appear, are:
- Report number and date. The number is the key to everything else: it is how the report is looked up and how the stone can be matched to it.
- Shape and cutting style, and measurements. The outline (round, oval, pear and so on), the facet arrangement, and the stone’s dimensions in millimetres. The diamond size calculator shows how millimetres and carats relate for each shape.
- Carat weight. A measured weight, in metric carats of exactly 0.2 g.
- Colour, clarity and cut. The grades on GIA’s scales, explained in the 4Cs guide. GIA assigns an overall cut grade only to standard round brilliants; other shapes receive polish and symmetry grades instead.
- Polish and symmetry. The finish of the facets and the precision of their arrangement, each graded separately.
- Fluorescence. The strength and colour of the stone’s glow under long-wave ultraviolet light. GIA’s description of “None” covers a range up to very faint. It is recorded for identification.
- Inscription. Any lettering laser-inscribed on the girdle, the stone’s thin outer edge, such as the report number.
- Comments. Identifying features not recorded elsewhere. Where a treatment is detected, such as laser drilling, it is described here, so this field is worth reading in full.
- Proportions diagram and clarity plot. A profile drawing of the stone’s measured proportions, and a map of its clarity characteristics, with a list of the most significant ones that support the clarity grade.
A Dossier is a shorter report with an inscription
GIA also issues a shorter document, the Diamond Dossier. GIA states that the Dossier is available for diamonds weighing between 0.15 and 1.99 carats, and that it includes a laser inscription of the diamond’s unique report number on the girdle. The Dossier therefore ties the paper to the stone by a number on the stone itself, which can be read under magnification and compared with the document.
Matching the report to the stone
A report describes one particular stone, and its usefulness depends on being sure it is the stone in hand. Three checks do most of the work. The report number can be looked up in GIA’s online Report Check, which returns the details recorded for that number. Where the girdle carries an inscription, it can be read under a 10× loupe and compared with the report. And the measurements and carat weight on the report should agree with the stone when it is measured and weighed.
A mounted stone is harder to check than a loose one, because the setting can hide the girdle and make weighing impossible. The carat weight of a mounted diamond can only be estimated from its measurements, which is a different thing from the weight on a report.
What a report cannot tell you
- What the stone is worth, or what anyone will pay for it. That is outside a grading report by design.
- Anything that happened after the examination date, such as chipping, wear or later treatment.
- Anything about the setting it is in. The metal is a separate question; the hallmarks reference covers what a stamp on it claims.
Read that way, a grading report is a precise description of a diamond by the laboratory that examined it. Its value lies in the description being independent, specific and checkable, not in any figure it puts on the stone, because it puts none.