Comparing Diamond Certificates: Who Can You Trust?

If you don’t know much about diamonds, how do you know a diamond is the quality a salesperson or computer screen says it is?

Comparing Diamond Certificates

When it comes down to it, you have to put your trust in either the certificate or the salesperson. I won’t go into salespeople in this post, but if the diamond is a 1/2 carat or larger it probably has a certificate stating the exact quality. But then, who is the diamond certified by? That will make a HUGE difference as to whether or not you can trust what it says!

Who’s the best? Who’s the worst? I’m not going to list all the grading labs out there. Frankly, there’s too many. I’ve listed the top 5 most common certificates you will see, including the most accurate and a few of the not-so-accurate.

GIA – The Gemological Institute of America

The GIA is by far the strictest and most accurate grading lab of them all. They invented the diamond grading system (color, clarity and cut scales) that most other companies use. Many people refer to the “premium” for GIA certified stones, but really it’s the true market value. GIA stones cost more, because you get more.

Keep in mind, while GIA is the most accurate, there are still GIA certificates out there that are just plain wrong. You can search the internet for instances where the same diamond was sent to be certified by the GIA three separate times, and each time it came back with a different grade. This isn’t a common scenario but it can happen because grading is more or less an “expert opinion.”

On a side note, if you do choose to buy any stone that is not certified by the GIA, I would compare it to a GIA certified stone of the same quality. Or, compare it to a GIA certified stone in the same price range. If the GIA stone is priced the same, then the quality of the GIA stone is likely the true quality of the diamond you’re comparing it with. GIA is the go-to certificate in the jewelry industry, hands-down.

AGS – The American Gem Society

The AGS certificate is popular among certain vendors and they are definitely one of the more honest grading labs and probably the most consistent next to the GIA. The only problem for the average customer is that the AGS uses a different grading scale with numbers 0-10 (zero being the best) for color, clarity, and cut. So, now the average person has to learn a whole different grading scale and the technicalities that go with it.

The AGS has also been making advancements in determining the quality of the cut of a stone, and are slowly becoming a more popular certificate because of this. Still, the majority of independent jewelry stores and online sites use GIA and other certificates.

EGL – European Gemological Laboratory

There’s a lot of confusion on the internet about EGL. What you need to know is there are two “EGL” companies that are completely separate and in no way affiliated with each other: EGL USA and EGL International (which includes EGL ISRAEL).


The certified stones I carry in my store are primarily GIA and EGL USA. An EGL USA certificate will commonly mark a diamond one or two grades higher than the GIA. Thus, EGL USA certified stones sell for about 15-20% less than their GIA counterpart. Keep in mind they can be accurate, too, and the price will reflect it.

I know some diamond forums like to hate on EGL certificates, but the fact remains there is a huge difference between EGL USA and all the rest. Still, you might have to put more of your trust in the salesperson or yourself when buying one of these stones.

EGL International

This includes a few different branches such as EGL ISRAEL. My advice is to stay far away from diamonds graded by EGL International. It’s not that the stone is “bad”, but the real problem is that their grading is so off you really have no idea what grade the diamond actually is. I have purchased a couple stones graded by EGL ISRAEL because I got a good price, but if I show them to a customer I will explain exactly what grade they are. Maybe the clarity is accurate, but the color is three grades off (it is certified D when it’s really a G). It may still be a nice diamond but the point is, you cannot trust this type of certificate. They are usually off more than one grade on more than one dimension. Because of this, you will find these stones at incredibly low prices, something like 60% less than RAP price.

IGI – The International Gemological Institute

There are several franchises among the IGI, and differences in grading among them. There is much debate on IGI, but the fact is they’re usually not as strict as the GIA or AGS. Another interesting thing to note is that the IGI provides reports for all diamonds sold by the Zales franchise. Now, not all stones sold by chain stores are bad, but Zales is very much a price point chain store with a multitude of low prices and low quality diamonds. For a laboratory to grade their stones exclusively, you might expect there to be a little incentive to make the diamonds look better on paper than they actually are. Heck, I don’t know. You might say it’s “just business”.


Like I said, just because a stone is graded by a certain laboratory doesn’t mean the stone is bad in any way, but you may not be able to trust exactly what the certificate says. Certification is a great starting point but I would also seek the salesperson or jewelry store with a “GIA” reputation.

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