IGI certificate explained: what the report actually tells you

An IGI report is a laboratory's opinion on a stone, not a guarantee of beauty. It is still the most useful document you will get, provided you read the right lines.

1. Report number and inscription

The report number should match the laser inscription on the girdle, which you can see under a loupe. If the seller cannot show you the inscription, the report may belong to a different stone.

2. The 4Cs

• Carat — weight to two decimals. A 0.99 ct stone is not a 1 ct stone, and the price difference is real.
• Colour — D to Z for diamonds. Lab-grown stones are usually D–F.
• Clarity — FL to I3. VS1 and VS2 are both “very slightly included”; the difference is visible only under magnification.
• Cut — for rounds, a grade from Excellent to Poor based on proportions and symmetry.

3. Growth method

CVD or HPHT. Both produce diamond; HPHT is often used to improve colour after growth. The report states which, and a reputable seller will tell you without being asked.

4. Measurements

This is the line most buyers skip. The report gives the stone's dimensions in millimetres — for a round, diameter and depth. A 1 ct round that measures 6.2 mm is cut too deep; one that measures 6.6 mm is well proportioned. The carat is the same; the look is not.

5. What the report does not tell you

It does not grade the setting, the polish of the metal, or whether the stone is eye-clean in daylight. It also does not guarantee the stone will look good in a particular setting — a deep stone in a low bezel will disappear.

How we use it

Every lab-grown diamond we ship is checked against its IGI report: weight on the scale, measurements against the seat, inscription against the number. The report travels with the piece. Loose lab-grown diamonds →