Diamond Grading

This introduction to diamond grading is meant to help you understand the basics of evaluating a diamond. Grading is not a single measurement but a disciplined reading of a stone — part science, part trained perception — and the foundation of everything else in this guide.

The grader’s eye

Grading rewards temperament as much as knowledge. The qualities that make a good diamond grader are quiet ones:

• A good, rested eyesight and the patience to use it slowly
• Objectivity — reading the stone, not the hope you have for it
• Integrity, and a strong sense of responsibility toward buyer and seller alike
• Concentration, attentiveness and the stamina to keep all three steady across a long parcel

The four characteristics

Polished diamonds are graded on what the trade calls the 4Cs — Colour, Clarity, Cut and Carat. Terminology and classification systems are set by three major institutions — GIA (the Gemological Institute of America), IDC (the International Diamond Council) and CIBJO — each with its own rules. This guide works in GIA and IDC terms.

Each of the four influences a diamond’s beauty, and through it the price. None of them stands alone: a flawless stone with a careless cut will disappoint, and a modest grade carried by a superb cut can outshine it.

Why certify

A certificate from an independent gemological laboratory is what turns a private opinion into a documented fact — an impartial record of a stone’s grades, and with it a reliable measure of its value. For a buyer not yet fluent in diamonds, that report is the firmer ground to stand on: choose a certified stone, and where you wish to be doubly sure, take the certificate back to the laboratory that issued it and have the report confirmed. The names that carry the most authority are GIA and HRD, the Antwerp Institute of Gemology; with either, a certificate can be checked against the laboratory’s own records online.