How to Read a Diamond Grading Report, Field by Field

Last updated: August 2026

What is actually on a diamond grading report?

A grading report is a description of one specific stone, written to a fixed template so that two stones can be compared line for line. IGI’s own summary of its diamond report lists the gemstone’s description — natural or laboratory-grown — followed by shape, cutting style, measurements and the 4Cs assessment, and notes that reports may also carry a graphic representation of the stone’s proportions and a diagram of its clarity characteristics.

That is the whole document. There is no hidden section, no overall score and no price. Everything a report does, it does by describing measurable or judged attributes and letting you compare them against another report.

What do the report number, the date and the shape line tell you?

The report number is the hook. It is the only field that lets you take the document back to the laboratory and ask whether the record is real, which is why it belongs at the top of any check. The date matters more than people expect: a report describes a stone as it was on that day, and a stone that has since been recut, repolished or damaged no longer matches.

Shape and cutting style are two fields, not one. Shape is the outline — round, oval, emerald, cushion. Cutting style is the faceting pattern applied to it, most often brilliant or step. A “rectangular modified brilliant” is a shape and a style stated together. If you are choosing between outlines rather than decoding one, oval vs round covers what the difference does at the same carat weight.

How do you read the colour and clarity grades?

Both are letters on a scale, and both are judged rather than measured. On IGI’s colour scale, D to F is colourless, G to J is near colourless, K to M is slightly tinted, N to P is very light colour, and S to Z is light colour, with fancy colours handled on a separate scale entirely. Grading is done with the stone face-down against master stones under controlled light, which is why a grade is a comparison rather than a reading.

Clarity runs IF for internally flawless, then VVS1 and VVS2, VS1 and VS2, SI1 and SI2, and I1 to I3. The grade reflects what a trained grader sees at 10x magnification — size, number, position and nature of the inclusions together, not just how many there are. A single inclusion under the table can outrank several near the girdle. The 4Cs explainer covers where each scale stops mattering to the eye.

What are the proportions diagram and the clarity plot?

They look similar and do opposite jobs. The proportions diagram is a side-on schematic with numbers: table percentage, depth percentage, crown and pavilion angles, girdle thickness, culet. Those numbers are measured, and they are the raw material behind the cut grade — they describe the geometry that decides how light moves through the stone.

The clarity plot is a face-up and face-down map of where the inclusions are, drawn in symbols with a key beside it. Red marks internal characteristics, green marks surface ones, and each symbol names a type — feather, crystal, cloud, pinpoint, needle. The plot does not grade anything. It locates. Two stones at the same clarity grade can have completely different plots, and the one whose inclusions sit under the crown facets rather than under the table will usually be the easier stone to live with.

What do the abbreviations in the comments mean?

The comments section is where a report stops being a form and starts telling you something. IGI publishes a glossary of the abbreviations it uses, and a handful of them change how you should read the rest of the page.

A jewellery report adds one more layer: IGI’s reports on finished pieces describe the article, identify the mounted gemstones and record precious metal content and purity stamps where they are present. That is the field that ties a diamond report to the stamp inside the shank.

Why can two reports on near-identical stones differ, and what can a report not tell you?

Because most of the document is expert judgment applied consistently, not instrument output. Carat weight and measurements are objective. Colour and clarity are calls made by a trained grader against masters, under controlled light, on a specific day. IGI says so plainly on its own verification page: a report is an opinion, not a guarantee, appraisal or warranty, and opinions may vary depending on when, how and by whom an article was examined. Two laboratories landing a grade apart is ordinary variance, not evidence of fraud — the IGI vs GIA comparison goes further into why.

What no report tells you: the price, whether the price is fair, how the stone looks to you, or — on its own — that the paper in front of you belongs to the stone in front of you. Those are answered by comparing like specifications on the day, by looking, and by checking the report number against the laboratory’s own records. Beyond Carat narrows the first problem by publishing a floor instead of one flattering stone: every diamond is graded by IGI, the International Gemological Institute, in D, E or F colour, VVS or VS clarity and Excellent cut, with the report in the box. The concession that comes with that: it is IGI only, with no GIA option, and a narrow band means Beyond Carat cannot be the cheapest seller of a given carat weight.

Frequently asked questions

What is the most important field on a diamond report?

Cut, for how the stone looks, and the report number, for whether you can trust the rest of the page. Colour and clarity move price hard but move appearance far less than buyers expect, and both are judged rather than measured.

What do the red and green marks on a diamond certificate mean?

They are the clarity plot. Red symbols mark internal characteristics such as feathers, crystals and clouds; green symbols mark surface features. The key beside the diagram names each symbol. The plot shows where inclusions sit, not how severe the grade is.

Does a higher clarity grade mean a better-looking diamond?

Not reliably. Above the point where inclusions stop being visible without magnification, extra clarity changes the price and not the view. Position matters more than grade at the margin: an inclusion under the table reads differently from one hidden beneath a crown facet.