Out of all of the gemmological grading labs, the most well known is arguably the Gemological Institute of America (GIA). However, other trusted and renowned labs include the two versions of the European Gemological Laboratory, i.e. EGL USA and ELG International, as well as the International Gemological Institute (IGI), the Hoge Raad voor Diamant (HRD), and the American Gemological Society (AGS).

In short: The three main diamond labs are GIA (gold standard, strictest grading), IGI (preferred for lab-grown, faster turnaround), and HRD (Antwerp-based, common across Europe). The same stone graded at GIA versus IGI typically differs by 1 colour grade and 1 clarity grade — IGI runs more lenient. AGS uses a 0-10 scale rather than D-Z, with cut grade leading. Always verify the girdle inscription against the report number.

One thing you need to recognise is that all of these laboratories differ in the way in which they grade diamonds, with some being stricter than others. It is widely accepted that the Gemological Institute of America has the strictest standards. Despite this, The American Gemological Society (AGS) is just as strict, the only difference between the two being the fact that the AGS is very new. It does stand out from the GIA in one respect and this is the fact that it has an extra grade for ‘cut’, ideal. The HRD is almost as strict is the GIA. However, nothing compares to the popularity of GIA certification.

If you were to compare a certificate from each of the gemmological laboratories you would see some distinct differences. Some use diagrams, others don’t, and they differ in their terminology, layout, and the grading systems they use. However, most experts will tell you that the two areas you really need to concern yourself with are clarity and colour. These two aspects are pivotal in terms of a diamond’s quality and appearance, and thus you need to be fully aware of the differences in the grading systems in regards to these two aspects. You will find further information below.

Let’s begin by looking at clarity. GIA is stricter than the other gemmological laboratories. One thing to note is that HRD has added an extra grade. This is known as ‘Loupe Clean’ and it is used to describe all stones that have invisible impurities. EGL USA and IGI often rank clarity by a grade or two higher. For example, a diamond ranked VVS1 by GIA is likely to also be ranked VVS1 by AGS and VVS1 or LC- by HRD. IGI would rank this diamond as VVS1 as well or IF-. Finally, EGL USA would grade the same diamond IF, and EGL INT. would grade the diamond FL.

When it comes to colour, GIA is again the strictest, although AGS and HRD are not far off their standards. EGL USA and IGI often rank colour by one to two grades higher than the other laboratories. For example, a diamond ranked ‘F’ by GIA is also likely to be ranked ‘F’ by AGS and HRD, yet ‘E’ by IGI and EGL USA, and finally ‘D” by EGL.