Diamond Grading Report

gemologist grading a diamond

Grading a Diamond Under Standard 10X

I can’t stress enough the importance of having a grading report in any diamond jewelry purchase you make. More commonly known as a “diamond certificate”, the grading report contains essential details about the qualities and characteristics of a particular stone. 

For consumers who want assurance that you are getting exactly what is described in a piece of diamond jewelry, you should only buy diamonds with reports issued by an independent gemological laboratory like GIA or AGS.

Besides the evaluation and assessment of a diamond, such reports are also important if you want to sell unwanted jewelry or if you are planning to buy an insurance policy to protect your investment.

The surprising behavior I noticed in the majority of shoppers is that they don’t pay enough attention to what is stated on the “certification”. In fact, most people simply take a casual look at the report and never give any deeper thoughts about the information inside it.

Before we delve deeper into analyzing details, I’m going to show you how to read a diamond grading report correctly first. Remember, knowledge is power. The more knowledge you have about diamonds, the better equipped you will be for making rational choices.


Using GIA Reports as a Benchmark

I am going to use a GIA diamond grading report to do a breakdown of various elements found in the “certificate”. The reason behind using GIA as the benchmark is that they are the foremost authority in gem grading and are highly recognized in the industry.

Here’s a quick historical trivia – Did you know GIA invented the system of grading diamonds with the 4Cs? Due to the elegance and simplicity of relaying a diamond’s gemological information, the grading system was well-received by both consumers and members of the trade. In fact, the majority of other gemological organizations adopt a similar version of GIA’s grading system today.

That is to say, if you are able to read a GIA report, you won’t have much difficulties with grading reports from other organizations like AGS or HRD. The main differences between these lab grading reports lie in the different nomenclature and classification terms used.

Anatomy of a GIA Diamond Grading Report

anatomy of a gia report

1. Header of the Report – Who Actually Graded the Diamond?

The first detail to look for is the name of the issuing laboratory. The more well-known labs are GIA, AGS, EGL, IGI, and HRD but there are also plenty of other “specialty services” who issue reports too.

The more important question here is who uses these specialty services and why? You might have encountered the notoriously “cheap” diamond deals that come with obscure grading reports from “independent” appraisers or in-house gemologists.

The truth is, there are no deals here. These “cheap” diamonds are usually what they are; low quality diamonds that aren’t worth the fees of sending it to a proper lab for grading. Instead, unethical jewelers bank on the lax grading standards of “independent” appraisals and biased in-house reports to make low quality diamonds sound better on paper.

The bottom line is that you should only consider buying diamonds graded by GIA or AGS. The other labs have lenient standards and often over-grade diamonds for the benefit of the jeweler. For more information, you can refer to our article on the differences between gemological labs.

2. Report Number, Cutting Style And Measurements

The next detail you would notice is the report number, which is a unique series of digits for record keeping purposes. Most labs retain this number in their database in case you misplace your report and need a replacement. More importantly, this number also allows you to have a direct verification of the document via the gemological lab’s website.

laser inscription on girdle of asscher cut

Laser inscription seen under 10X on the girdle of an Asscher cut

Continuing downwards, you can find information about the diamond’s characteristics, listed in this order: shape and cutting style and measurements. The first feature describes the shape of the stone and its cutting style, such as round brilliant or pear modified brilliant. After that, you can see information about the diamond’s physical dimensions measured to the nearest hundredth of a millimeter.

3. The Four Cs – Classification And Attributes

Moving on to the next section is the carat weight, which describes the weight of the stone measured to the hundredth of a carat. The color grade is based on an assessment of the lack of color in the diamond. Color grades start from D to Z and the fancy color grading system is applied if a diamond displays a color intensity beyond the Z color rating.

The clarity grade is determined by a gemologist who examines the stone under 10X magnification for inclusions and imperfections.

If the diamond is a standard 57 facets round brilliant, all reports dated after 2006 will include a cut grade. The cut grade is assigned based on a scale of excellent to poor in a GIA report. For the layman, this is one of the most essential qualities to look out for since it directly affects the brilliance and sparkle of the diamond.

With that said, each of these Cs are important factors for consideration when you are buying a diamond. I had covered each topic extensively in different sections of our website. For more details, make sure you use the header menu of the website and navigate to the corresponding categories.

4. Additional Grading Information

understanding a diamond lab report

Inspection Process

The finish of the diamond is influenced by 2 factors; polish and symmetry. The ratings assigned here will affect the shape appeal and cut grading as they contribute towards the diamond’s appearance.

Polish is an indication of how smooth the diamond’s surface is. A well-polished diamond can produce crisp looking reflections and undistorted light transmissions. Symmetry is the comparison of how the stone’s facets are aligned in relation with one another. For detailed information on polish and symmetry, click here.

The next feature you can find in this section is the description of the diamond’s fluorescence properties. The fluorescence a diamond is described based on the intensity and the color it glows with when exposed to ultraviolet (UV) light.

Is fluorescence a friend or a foe? This is perhaps one of the most misunderstood diamond property and there is a lot of misinformation about fluorescence. We addressed those questions here and I strongly encourage you to read this article if you intend to buy a diamond with fluorescence.

Under the “Other Comments” section, all other miscellaneous information about the diamond will be listed here. For example, laser inscriptions (if any), additional details to help with identification and clarity characteristics that are too complicated to be plotted in the reference diagram can be found here.

While most comments made in this segment are benign, there are a couple that raise a red flag and requires closer examination. This article takes an in-depth look at all the possible notes made under the “Other Comments” segment and shows you what to look out for.

5. Reference Diagrams

Every diamond is unique in terms of its clarity characteristics. Like our fingerprints, the clarity plot diagram is a graphical representation of the diamond’s “birthmarks”. When looking at the symbols and identifying the types of flaws, you should pay extra attention to what you see.

Blemishes (external) are marked in green color while inclusions (internal) are marked in red. If you are interested to see how the different clarity characteristics look like in real life, head over to this page here to view photographs and diagrams.

Next, you find the critical proportions of the stone indicated in a profile view. This proportions diagram is useful for people who wish to analyze the diamond based on numbers like table %, depth %, crown angles, pavilion angles and girdle thickness. Note: The proportions diagram given for fancy shapes usually omit values for crown and pavilion angles.

On the proportions diagram, the presence of a culet and the girdle thickness are also indicated. For modern brilliant cuts, the absence of a culet (None) is preferred because a large culet can actually cause the appearance of the diamond to detract from its usual appeal. For girdle thickness, a range between thin – slightly thick is preferred so that the diamond faces up bigger.

the complete folded certification

6. Security Features And Authenticity Marks

In the final part of the report, you should look out for security features as they can help prove the authenticity of the document. Typically, these security marks come in the form of a hologram, a universal product code or an embossed stamp. For a peace of mind, most labs provide an online verification service where you can perform an instant verification. For your convenience, we have compiled a list of URLs where you can do the checks here.

Shopping based on a certificate alone is risky and fraught with uncertainty. Instead, you can see actual diamonds in 360° at JamesAllen.com and buy with confidence.

How to Read a Diamond Certificate – A Video Summary


In-depth Articles on the Different Elements of Lab Reports:

  • Depth And Table Values in the Proportions Plot
    These are the 2 most important values in a diamond’s proportion plot. However, these 2 values by themselves aren’t enough to tell you how a stone looks like in real life and you need more data to work with in conjunction to these values.
  • Importance of a Diamond’s Girdle Thickness
    The diamond’s outermost circumference is called the girdle. The girdle thickness can range from different values depending on how the diamond was cut. This leads us to the following questions. What kind of girdle thickness is optimal? Is the finishing on the girdle of importance? You will find answers in this article.
  • Other Comments Section of a Lab Report
    Gemological lab reports contain a section called “Other Comments” in which lists clarity features of the diamond that aren’t plotted in the graphs. Most of the times, the clarity characteristics listed here are minor issues but it pays to take a closer examination.
  • HRD Diamond Certification Lab – Are They Reliable?
    GIA, AGS and EGL are the major players in the grading industry. Besides them, one of the gemological lab that is very popular in Europe is the HRD lab. This begs the question: is a certificate from HRD any good? Find out more in this review…

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  1. Avatar
    May 5, 2013 at 4:44 am

    Under the girdle thickness area, what do you mean by finish? My GIA report states that the girdle is faceted. Is this normal?

  2. Avatar
    Paul Gian-
    May 6, 2013 at 12:57 pm

    A faceted girdle is normal and is usually the type of finish that people like to see. Hence, the reason why cutters polish them in this manner. You can find out more here: https://beyond4cs.com/grading/girdle-thickness/does-finishing-matter/

  3. Avatar
    Greg W.-
    June 20, 2016 at 3:48 pm

    I’m looking for diamond classification charts where I can see the amount of flaws in each category. Can you help?

  4. Avatar
    Paul Gian-
    June 20, 2016 at 3:51 pm

    I think you are probably referring to the classification of diamond clarity ratings. This information can be found here: https://beyond4cs.com/clarity/

  5. Avatar
    July 18, 2016 at 4:22 am

    Hi Paul,

    Very interesting article, I do find something new whenever I come to this web. Thanks alot and keep updating.

  6. Avatar
    February 22, 2017 at 4:25 pm

    Hi Paul,

    Do the first digit (s) of an GIA report number mean anything (such as which mine the diamond is from or any other characteristic)?
    Thank you.

  7. Avatar
    Paul Gian-
    February 23, 2017 at 5:05 am

    Nope. As far as I know, it doesn’t mean anything like that.

  8. Avatar
    Vincent Schneider-
    February 25, 2017 at 6:28 pm

    Hi, I recently viewed a website which is
    a diamond assessing center on Fifth Avenue close to the diamond district. It is a service, not a jeweler, which offers drop-in assessments of diamonds for low or no charge, so that the seller can go to a jeweler with some sort of idea of value in advance. I have mislaid the link to this service, and I hope that you might give it to me. Thank you for your help.

    VIncent Schneider

  9. Avatar
    Paul Gian-
    February 26, 2017 at 2:43 am

    What’s the point in doing so? Possibly paying a fee to find out the “value” of a diamond sounds illogical and silly.

    You can use the techniques outlined here to do that for free and with good accuracy – https://beyond4cs.com/diamond-prices/

  10. Avatar
    September 13, 2017 at 8:46 pm

    Hi Paul,

    First off, great website! All your advice has really helped me find and choose a diamond.

    I had a question regarding inscriptions.

    I recently bought a GIA-certified loose diamond (1.2 ct, VS2, H) from James Allen, but it was not inscribed with the GIA report number. The JA rep said I could send the diamond to GIA to get it verified and inscribed, but do you think that’s worth it?

    I’m not planning on selling the diamond, but I am worried about my local jeweler accidentally swapping the diamond while working on the setting/band. Are my fears overblown or should I just bite the bullet and send it to GIA to get it inscribed?

    Thank you!

  11. Avatar
    Paul Gian-
    September 14, 2017 at 6:31 am
  12. Avatar
    September 14, 2017 at 6:37 pm

    Thanks Paul! I read the article, and it makes sense.

    However, when I look at my diamond through a 20x loupe, I can’t find any inclusions myself, and I can’t even find the small inclusions listed on the GIA report. Since your article relies on the unique inclusion plot to ID the diamond, I’m still a little concerned that I could be fooled. I’m probably overthinking all of this though…

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