How to read a diamond certificate: what each section says

A diamond certificate is a grading report issued by an independent gemological laboratory. It describes the stone; it is not an appraisal and does not state its price.

Which laboratories issue them #

GIA, IGI, HRD and AGS are some of the best known. The standards and strictness of each laboratory are not identical, so two diamonds with the same grade from different labs may not be comparable.

Main sections #

• Report number: identifies the stone and lets you verify it on the laboratory's website.
• Type: whether it is a natural or a lab-grown diamond. See natural and lab-grown.
• Shape and cutting style: for example, round brilliant. See gem cuts.
• Measurements: diameter and depth, in millimeters.
• Carat weight: each carat is 0.2 g.
• Color: from D (colorless) to Z (light yellow).
• Clarity: from FL (flawless) to I3 (inclusions visible to the naked eye).
• Cut: in the round brilliant, from Excellent to Poor; it includes polish and symmetry.
• Fluorescence: reaction to ultraviolet light; in some stones it can show as a milky tone.
• Clarity plot: a diagram that marks the inclusions.
• Comments and laser inscription: many stones have the report number engraved on the girdle, visible under a loupe.

The 4Cs #

Color, clarity, cut and carat. See the 4Cs of diamond.

Do I need a certificate? #

For diamonds of a certain size and value it is highly recommended. For small stones the cost of the report may not be worth it. Always check that the report number matches the inscription on the stone and that the laboratory is a recognized one.

A certificate is not #

• An appraisal: it does not say what it is worth.
• A guarantee of beauty: two stones with the same grades can look different.
• A certificate of the jewel: it only describes the diamond.