How to Read a Diamond Grading Report

Two diamonds can look almost identical to the eye and still differ greatly in quality and value. A grading report from an independent laboratory is how buyers and sellers agree on exactly what a stone is. Knowing how to read one protects you and helps you compare diamonds fairly.

What a grading report is, and what it is not

A grading report is a laboratory's scientific description of a diamond: its weight, measurements, colour, clarity, cut and other characteristics. It is not an appraisal and does not state a price. Two stones with similar reports can still be priced differently because of factors such as proportions, fluorescence or market demand.

The most widely recognised laboratories are the Gemological Institute of America (GIA), which introduced the 4Cs grading system, and the International Gemological Institute (IGI). Both issue reports for natural diamonds.

The key lines on a report

• Report number: a unique number you can verify on the laboratory's website. Many diamonds also carry this number laser-inscribed on the girdle.

• Shape and cutting style: for example Round Brilliant, Oval Brilliant or Emerald Step Cut.

• Measurements: the stone's dimensions in millimetres.

• Carat weight: recorded to two decimal places, for example 1.02 ct.

• Colour grade: from D (colourless) down to Z (light yellow or brown).

• Clarity grade: from FL (flawless) through IF, VVS1, VVS2, VS1, VS2, SI1, SI2 to I1, I2 and I3.

• Cut grade: for round brilliants, from Excellent to Poor. Polish and symmetry are graded separately.

• Fluorescence: how strongly the diamond glows under ultraviolet light, from None to Very Strong.

Origin and treatments

A report states whether a diamond is natural or laboratory-grown, and notes any treatments detected. For natural diamonds, this is one of the most important lines on the page: it confirms you are paying for a stone formed in the earth.

Three quick checks before you buy

• Verify the report number on the laboratory's official website.

• Ask to see the girdle inscription under a loupe and confirm it matches the report.

• Compare the measurements and carat weight on the report with the stone in front of you.

If you would like help reading a report for a stone you are considering, our team at Anjanee Diamonds is happy to walk you through it during a consultation.