When you buy an engagement ring, online or in-person, the center diamond will almost always have a certificate from a third-party laboratory. (In fact, if it doesn’t, run the other way as fast as you can!). This certificate is usually called a diamond certificate or diamond grading report.
There are some things that you need to know about these diamond certificates in order to properly evaluate diamond quality and value.
1. This is where the 4 C’s (cut, color, clarity, and carat) come from. This isn’t a guide on how to choose a diamond based on the 4 C’s (for that, see our Engagement Rings 101: A Crash Course guide).
2. There are multiple labs that produce diamond certificates.
3. All diamond labs are not equal. Or, more importantly, certicates from all diamond labs are not equal. Why? Some labs grade diamonds more strictly than others. That means that a VVS2 clarity grade from one lab might not be equal to a VVS2 clarity grade from another.
Let’s break this down and look at what you need to know:
About Diamond Grading
Labs are sent diamonds after they are cut so that they can examine it and issue a diamond certificate grading the diamond’s attributes. All labs grade the same characteristics (color, clarity, carat, etc) and, for the most part, they use the same scale (D is highest color grade, FL is highest clarity grade, etc).
However, as mentioned above, diamond labs (and their certificates) differ in their strictness in grading and attention to detail. Here’s a list of common diamond labs and how credible each one is:
Common Diamond Labs
GIA – Gemological Institute of America
The GIA is the most commonly used diamond lab. If you’re looking at a diamond online, chances are it’s graded by the GIA. The GIA is a very credible lab — their grades are trustworthy and reputable.
GIA Credibility Rating (1-10): 10
AGS – American Gem Society
The AGS (more specifically, their grading department: AGS Labs) is another trustworthy and accurate lab. They’re also known for very in-depth cut grade reports, and are the pioneers of the Ideal cut grade for a diamond.
AGS Credibility Rating (1-10): 10
IGI – International Gemological Institute
The IGI is a step below the GIA and AGS with regards to grading strictness and credibility. Their certificates still have value, but if you’re looking at an IGI report, keep in mind that the diamond might not have been graded as strictly as it would have been by the GIA or AGS.
IGI Credibility Rating (1-10): 7
EGL – European Gemological Laboratory
EGL certificates are a bit less strict than even IGI certificates. You can generally be pretty sure that a diamond graded by the EGL received slightly better grades than it would have been if it had been graded by the GIA or AGS.
EGL Credibility Rating (1-10): 6
There are other labs, but these are the most common. Now, let’s see how this impacts you:
How Does This Affect Your Engagement Ring Search?
The main impact that the differences between diamond labs has on your engagement ring search is pricing of your diamond. Sometimes, seemingly identical diamonds have vastly different prices. Why?
Many times, the difference in prices is due to each diamond being graded by a different lab. For example, you might see 2 different diamonds. Both are 1 carat, Ideal cut, F-color, VVS2 clarity, and even similar grades for more advanced characteristics (depth %, table %, fluorescence, etc), however, 1 diamond is $2,000 less than the other one. In this situation, check the lab that graded each diamond.
You’ll likely see that they were graded by different labs, one being a more credible lab (AGS or GIA) and one by a less strict lab (EGL, for example). This means that these diamonds, despite their grades, are not identical. The grades from the less strict lab probably wouldn’t have been awarded to that exact same diamond by the more credible lab. In this example, the diamond that was graded by the EGL would have probably scored Very Good cut, G-color, and VS1 clarity (carat grades are almost always consistent across labs). This explains the price difference between these two seemingly identical diamonds.