Why does a diamond grading report matter? GIA (the Gemological Institute of America) aims for its reports to give an unbiased, expert evaluation that helps a buyer make an informed decision.4 A report is not an appraisal, which is an estimate of a stone’s money value. A diamond’s value may rise or fall over time, but its qualities are unlikely to change.3
How does it work? A laboratory examines the stone and records the 4Cs: cut, colour, clarity and carat weight. A full GIA Diamond Grading Report also has a diagram plotting clarity characteristics (the shorter Diamond Dossier leaves this out), such as inclusions (tiny marks inside the stone), a graphic of its proportions and a unique report number.2 A report also confirms the stone is a diamond and names any known treatments.3
What should you keep in mind? Results reflect the methods and equipment used at the time, and another examination may differ.1 Laboratories may also follow different standards, so the same diamond can receive different grades.5 A grading report is sometimes called a "certificate".3 CIBJO, the World Jewellery Confederation, uses that word for a document of legal standing.6 To see how laboratories differ, read GIA vs IGI diamond reports.
Example: Imagine two round diamonds, each recorded as 1.00 ct, because a GIA report gives carat weight to the nearest hundredth of a carat. Their reports grade one G and the other J on the same D-to-Z colour scale, so you compare like with like instead of relying on a sales description.2 Neither report gives a price. You can also enter a GIA report number on GIA Report Check, because a printed or shared copy may not include every update to the grading information.1