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How are Certified Diamonds Different from Regular Diamonds?

March 13, 2015

Technically, there is no difference between a certified diamond and a "regular" or non-certified diamond.  However, that doesn't mean that a certification is unimportant.

Any diamond can receive a grading report and be "certified", and most diamonds over 3/4ct are, especially if they're the center diamond of a diamond engagement ring.  However, which laboratory graded the diamond and the specifics of the report can make a large difference in the desirability and price of the diamond.  But again, there is technically no difference, except for the certified diamond receiving a third-party grade from an independent lab.

Who Certifies a Diamond?

The reason that certified diamonds typically sell for more than non-certified diamonds, is because an independent laboratory has measured and given their opinion on the grade of the diamond.  The key word here is independent. The grading report from a laboratory is valuable, because the lab has no part in the business of selling diamonds, only grading them.

The Gemological Institute of America or GIA, began the process of independently certifying diamonds, and is still considered to be the most accurate and reputable laboratory in the industry.  This is because they created the original grading scales and still adhere to those grades the closest.  So, generally speaking, a diamond with an "H" color grade in 1980, will still look like an "H" color today.

Accuracy and consistency are important in diamond grading because many important diamond grading factors, such as color and clarity, are opinions.  The GIA has held the most consistent with their grading standards over the years, giving them the strongest reputation.  This reputation causes GIA certified diamonds to sell for a premium over other labs.

So Who Are the Main Labs and How Are They Different?

In addition to the GIA, the other major labs you'll see are the AGS and EGL, in addition to many smaller labs such as IGI or HRD.

One example I often use to explain the differences between the labs is to think back to your teachers in school.  Some teachers were notoriously difficult graders, while some were more lenient.  Technically, all teachers are supposed to be identical in issuing grades, and are using the same letters to issue those grades.  However, two teachers could be given the exact same paper, and one could grade it an A- and the other grade it a B+.

In my opinion, who's grade is technically correct, is less important than understanding that these differences of opinion occur, and what they mean to you.

GIA and AGS have a reputation as being harder graders, while EGL and IGI are more lenient.  The hundreds of other labs will vary in their accuracy.

What Information is on a Certificate?

A certificate will have a combination of technical measurements and angles of the diamond, such as diameter, depth percentage, table percentage and crown angle, as well as subjective grades like color, clarity, polish, and symmetry.

You will also receive proof that the diamond was naturally formed and not synthetically created.  Often the certification will also contain a plot, which maps the inclusions and blemishes on a diamond.  Think of it like a unique fingerprint for a diamond, since no two diamonds have identical inclusions.

These measurements and opinions help determine the price of the diamond and help you identify the diamond as your own in the future.

The Bottom Line on Diamond Certification

Diamond certification is an incredibly complex and nuanced topic.  On the surface, it's as simple as, "has this diamond been graded by a laboratory?".  However, as you dig deeper and learn more, you can get caught up in a maze of letters and numbers.

The most important piece of advice I can give you is to look at several different diamonds, in person, from different laboratories, and begin to educate yourself.  I don't believe in "good" or "bad" diamonds, just different diamonds.  A diamond with a softer grade from EGL can look better than a diamond with an accurate grade from GIA, and cost less money.  The key when purchasing a diamond is to work with someone who will be upfront and honest about grades, and explain their differences.

At Mullen Jewelers, we are an AGS accredited store, and have gemologists, my father and myself, trained by the GIA.  We believe in grading as accurately as possible, and educating our customers when a certificate differs from our opinion.  We don't discriminate, we offer diamonds from any lab in addition to non-certified diamonds.

Would you like to learn more?  Have additional questions?  Please give me a call at 508-673-2251 or send me an email at






1 Response

Dorothy Davis
Dorothy Davis

September 09, 2020

Thank you so much for the information about certified and not certified

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