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 recognized 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 worldwide 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 color and clarity, for their evaluations largely determine the price of a diamond and yet they are not consistently graded across the board. A color grade, for instance, may differ in up to two grades (sometimes more) from one certificate to another and yet this is not always reflected in the price, so beyond understanding simply how color or clarity grades work, it is essential to know how to interpret and compare them.
Besides the 5 popular types of certificates that reputable jewellers offer, there are a multitude of other types of certificates not always independent, such as "in house" certificates which are typically graded more generously even than EGL International certificates and which cannot be compared with independent internationally recognised certificates.
Overall, the GIA tends to be the strictest on color 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 color grade higher than GIA, and EGL up to 2 color grades higher. So an F color 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 our experience.):
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| Diamond Certificate Comparison | GIA | AGS | HRD | IGI | EGL USA | EGL INT. | In-house Certificates |
|---|---|---|---|---|---|---|---|
| White | D | D | D | D+ | D+ | D+ | D+ |
| White | E | E | E | D | D | D+ | D+ |
| White | F | F | F | E | E | E+ | D+ |
| White | G | G | G | F | F | E | D |
| White | H | H | H | G | G | F+ | D/E |
| Extremely faint yellow tint | I | I | I | H | H | F | E/F |
| Very faint yellowbrown tint | J | J | J | I | I | G | F/G |
| Faint yellowbrown tint | K | K | K | J | J | H | G/H |
| Yellowishbrownish tint | L | L | L | K | K | I | H/I |
| Medium to strong yellowishbrownish tint | M | M | M | L | L | J | I/J |
| Strong yellowishbrownish tint | N | N | N | M | M | K | K/L |
| Very strong yellowishbrownish tint | O-P | O-P | O-P | N | N | L | L/M |
Certificate comparisons for color.
When it comes to comparing lab grading entities, it's more important to watch for consistency than strictness of grading. For example, the GIA will not grade a diamond the same way the IGI rates a diamond. The reliability of the color and clarity grades and in some instances the cut grades is only as good as the certifying lab's reputation. But if one lab consistently gives a single clarity grade higher than another lab, that lab is by no means less authentic. (Note - Although not published anywhere, these differences are generally accepted within the diamond trade as correct and are also based on our experience.):
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| Diamond Certificate Comparison | GIA | AGS | HRD | IGI | EGL USA | EGL INT. | In-house Certificates |
|---|---|---|---|---|---|---|---|
| 100% Eye Clean | FL/IF | IF | LC+ | IF+ | IF+ | IF+ | IF+ |
| 100% Eye Clean | VVS1 | VVS1 | LC-/VVS1 | IF-/VVS1 | IF | IF+ | IF+ |
| 100% Eye Clean | VVS2 | VVS2 | VVS2 | VVS2 | VVS1 | IF+ | IF+ |
| 100% Eye Clean | VS1 | VS1 | VS1 | VS1 | VVS2 | IF | IF+ |
| 100% Eye Clean | VS2 | VS2 | VS2 | VS2 | VS1 | VVS1/VVS2 | IF+ |
| 80% Chance | SI1 | SI1 | SI1 | SI1 | VS2 | VVS2/VS1 | VVS1/VVS2 |
| 10% Chance | SI2 | SI2 | SI2 | SI2 | SI1 | VS1/VS2 | VVS2/VS1 |
| Not Eye Clean | I1 | I1 | P1 | SI3 | SI2 | VS2/SI1 | VS1/VS2 |
| Not Eye Clean | I2 | I2 | P2 | I1 | SI3 | SI1/SI2 | VS2/SI1 |
| Not Eye Clean | I3 | I3 | I3 | I2 | I2 | SI2/SI3 | SI1/SI2 |
| Not Eye Clean | N/A | N/A | N/A | I3 | I3 | I1 | SI2/SI3 |
Certificate comparisons for clarity.
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.
