Diamond Knowledge

How to Read a Diamond Grading Report

A grading report turns a diamond from a leap of faith into something you can actually check. Here is how to read one — in plain English, whichever laboratory issued it.

← Part of the Brilliani Labs Diamond Guide

What is a diamond grading report?

A diamond grading report is an independent, expert assessment of a diamond's characteristics. Its value is that it is proof rather than opinion: a qualified laboratory, with no stake in the sale, examines the stone and records what it finds. For the wider picture of how diamonds are described and judged, see the Diamond Guide.

What information is on a report?

Reports vary in layout from laboratory to laboratory, but they tend to record the same things. Typically you will find:

• A unique report number
• The shape and cutting style
• Measurements
• Carat weight
• Colour grade
• Clarity grade
• Cut grade (for round brilliants), plus polish and symmetry
• Fluorescence
• A statement of whether the diamond is natural or laboratory-grown
• Any treatments
• Comments
• A clarity plotting diagram
• A proportions diagram
• Any girdle inscription

What's the difference between a grading report and an appraisal?

A grading report describes the diamond's quality; an appraisal estimates a monetary value, usually for insurance. They are different documents and serve different purposes — one tells you what the diamond is, the other puts a figure on what it might cost to replace.

How do I check a report is genuine?

Look up the report number on the issuing laboratory's own online verification database, and check that the number matches any inscription on the diamond's girdle. If the details on screen match the document in your hand — and the inscription on the stone — you can be confident the report belongs to that diamond.

What is the plotting diagram?

The plotting diagram is a map of the diamond's clarity characteristics — its inclusions and blemishes — marked with symbols on a diagram of the stone, so you can see roughly where they sit. It is, in effect, a fingerprint of that particular diamond.

What does the proportions diagram show?

The proportions diagram shows the measurements that drive a round brilliant's appearance: table size, total depth, crown and pavilion angles, girdle thickness and culet. These are the figures behind how the stone returns light. For what each of these parts is and where it sits, see the anatomy of a round brilliant.

Do all laboratories grade the same way?

They follow broadly the same Four Cs, but strictness and consistency can vary between laboratories. It is worth sticking to recognised laboratories and comparing like with like — a grade from one lab is not always identical to the same letter from another.

Does a report cover lab-grown diamonds?

Yes. Lab-grown diamonds receive dedicated reports that are clearly marked as laboratory-grown, so the diamond's origin is never in doubt. For how lab-grown and natural diamonds compare, see lab-grown vs natural.

Why does a report matter when buying?

A report lets you see what you are buying, compare stones fairly, and confirm both origin (natural or lab-grown) and any treatment — instead of taking the seller's word for it. It is the difference between trusting a description and being able to check it.