What people call a diamond certificate is officially a grading report. An independent laboratory examines the loose stone and records its properties. It is a description, not a guarantee and not a valuation.
The main laboratories
- GIA (Gemological Institute of America), founded in 1931. It developed the four Cs and the grading system the whole trade uses, and is regarded as the strictest reference.
- HRD Antwerp, the laboratory of the Antwerp diamond trade, widely used in Europe. Read more about Antwerp.
- IGI (International Gemological Institute), founded in Antwerp in 1975. It grades a large share of the world's lab-grown diamonds.
Laboratories do not grade identically. The same stone can come out a grade higher or lower at another lab, so compare stones graded by the same laboratory.
What is in a report
- shape and measurements, and the weight in carat
- colour and clarity grade, see the four Cs
- cut grade, for round brilliants only
- polish and symmetry
- fluorescence
- a diagram of the inclusions, on full reports
- for a lab-grown diamond: the statement that it is laboratory-grown
- a unique report number
Checking a report
The report number is usually laser-inscribed on the girdle, the thin edge of the stone, and can be read with a loupe. All three laboratories let you look up a report by its number on their website. Do both: the number on the stone must match the report, and the report must match the lab's own record.
When you need one
For a centre stone of some size, a report is the normal basis for the price. Small diamonds, such as those in a halo or a band, are not graded individually. The goldsmith buys them in a stated quality range.
Coloured stones
For sapphire, ruby and emerald a report serves a different purpose: it establishes whether the stone is natural, how it has been treated, and sometimes where it comes from. Laboratories known for this include SSEF and Gübelin in Switzerland, GRS, AGL in New York, and GIA. Read more about coloured stone reports.
Not a valuation
A grading report states no value. For insurance you need a valuation.