GIA vs IGI

The Gemological Institute of America, GIA, was founded in 1931. It developed the 4Cs and the D to Z colour scale that the whole industry now uses, and it is a non-profit organisation focused on research and education as well as grading. For natural diamonds, many in the trade regard GIA as the benchmark.

The International Gemological Institute, IGI, was founded in Antwerp in 1975 and has laboratories around the world. It grades natural diamonds, coloured stones and jewellery, and it is one of the most widely used laboratories for lab-grown diamonds.

Both issue reports that identify the stone and describe its quality: shape and measurements, carat weight, colour, clarity, cut where it applies, polish, symmetry and fluorescence, with a plot of the inclusions for larger stones. Both state whether a diamond is natural or lab-grown, and note any treatment they detect.

Formats differ, and they change over time, particularly for lab-grown diamonds. Read the report in front of you rather than relying on what a laboratory did in the past.

Grading involves judgement, especially for colour and clarity, and laboratories do not always land on exactly the same grade for the same stone. Many in the trade consider GIA the strictest benchmark for natural diamonds. That is why it makes sense to compare stones graded by the same laboratory, and to look at the stone itself rather than comparing two reports from different laboratories line by line.

Most graded diamonds carry the report number laser-inscribed on the girdle, invisible to the eye but readable under magnification. Both laboratories let you check a report number online. Make sure the number, the measurements and the carat weight match the stone you are buying.

Every diamond we set comes with an independent grading report. We will show you the report, help you read it, and present stones side by side on paper before anything is bought. Our certification guide explains what to look for.