The most renowned and trusted Gemmological grading laboratories are the Gemological Institute of America (GIA), the American Gemological Society (AGS), the Hoge Raad voor Diamant (HRD), the International Gemological Institute (IGI), and the 2 versions of European Gemological Laboratory (EGL International and EGL USA). From these 5 laboratories, the 3 that set the standard are the GIA, AGS & HRD.

The GIA is widely regarded as the most reputable and recognised grading laboratory in the world, with the strictest standards. Founded by the creator of the GIA, The American Gemological Society (AGS) is a newer certification and markets itself around the fact that it offers an Ideal cut grade which is one higher than the Excellent from GIA and is as strict as GIA in every respect. The Hoge Raad voor Diamant (HRD) or Diamond High Council is almost as renowned world-wide as GIA but not as popular and it is 95% as strict in its grading.

BEWARE: Even though these are the 5 leading international diamond certification organisations their grading criteria do vary and are not equally strict. Please be aware of the differences when choosing your diamond (see below).

All the certificates differ slightly in layout, terminology and grading systems, with some including diagrams and symmetry or proportion grading and others being simpler. However, the two main grading aspects to consider when comparing certificates are colour and clarity, for their evaluations largely determine the price of a diamond and yet they are not consistently graded across the board. A colour grade may differ in up to two grades from one certificate to another and yet this is not always reflected in the price, so beyond understanding simply how colour or clarity grades work, it is essential to know how to interpret and compare them.

All of this information seems very confusing, I hope I have explained the differences in a reasonably straightforward way.

Overall, the GIA tends to be the strictest on colour grades, and out of the other laboratories, HRD and AGS are the two that most closely adhere to the standards set out by the GIA. IGI and EGL USA tend to give one colour grade higher than GIA and EGL up to 2 colour grades higher. So an F colour stone on a GIA certificate would most likely be the same on HRD and AGS, an E on IGI or EGL USA, and a D on EGL. Please refer to the table below for a more detailed comparison*

*Note: Although not published anywhere, these differences are generally accepted within the diamond trade as correct and are also based on my experience.

Again, with clarity the GIA is said to be the strictest, giving at least one grade lower than all other laboratories. The HRD adds its own clarity grade to the traditional scale, terming all stones with impurities invisible with a 10x loupe as “Loupe Clean.” Because of this extra category, stones grades as IF or FL by the HRD would only receive a VVS1 from the GIA. The same applies for IGI, EGL and EGL USA, which would all grade between one and two clarity grades higher than the GIA, meaning that a VVS2 on a GIA certificate would grade as a VVS1 on an IGI and EGL USA and as IF/FL on EGL INT. while the majority of AGS clarity grades are equal to the GIA. Please refer to the table below for more detailed comparisons*.

Note: Although not published anywhere, these differences are generally accepted within the diamond trade as correct and are also based on my experience.

The main other differences between the certificates lie in the differences between GIA, HRD and AGS. GIA gives separate grading for symmetry and polish which the HRD groups together under the heading of “finish.” HRD also includes one clarity grade termed “Loupe Clean” which is not offered by the GIA. The AGS provides more information on the cut grade and offers one grade higher than the traditional poor-to-excellent scale of GIA, called “ideal cut,” as well as a number scale from 0-10 on which to grade diamond cut.