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. Sometimes called a diamond certificate, a grading report contains essential details of the qualities and characteristics of a particular stone. 

For the general consumer who want to know exactly what you are getting in a piece of diamond jewelry, you should only buy diamonds that have 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 your unwanted jewelry or if you are planning to buy an insurance policy to protect your investment.

The surprising behavior I found that in the majority of shoppers is that they don’t really pay attention to what is stated on the certification. In fact, most simply take a casual look at the report and never give a deeper thought about the information they are reading.

Before we even delve deeper on analyzing details, I’m going to show you the basics of how to read a grading report correctly. 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 the Benchmark

I am going to use a GIA report to do a breakdown of the different elements in the certification. 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.

Did you know that GIA was also the first to come up with the system of grading diamonds with the 4Cs? Due to the simplicity of relaying crucial information with their grading system, all other labs started to implement a modified version of GIA’s system within their operations.

That is to say, if you are able to read a GIA report, you won’t have difficulties with the others. The main differences in reports issued by other labs are that they might use different nomenclature or classification terms for essentially the same information.

Anatomy of a GIA 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 better known issuing labs are GIA, AGS, EGL, IGI, and the HRD. However, there are dozens of specialty services who can also issue reports.

For example, you might frequently see “cheap” diamonds with obscure grading reports from like independent appraisers or in-house gemologists. They are usually what they are; cheap and low quality diamonds that aren’t worth the fees of sending to the labs. Jewelers bank on biased in-house reports to make them sound better on paper.

You should only consider diamonds graded by GIA or AGS. The rest of the labs have lenient grading standards and are often under-grading the diamonds so that jewelers can sell them for more money. For more details, refer to our article on the differences between the different gemological labs.

2.Laser Inscription, Cutting Style And Measurements

The next detail is the report number, which is a unique number for the purpose of keeping records. Most labs retain this number in case you misplace your report and they also allow a direct verification of the document via their website. Also, certain reports include a laser inscription number which appears below the laser inscription registry.

laser inscription on girdle of asscher cut

Laser inscription seen under 10X on an asscher cut

Continuing downwards, you can read the details of the diamond qualities, listed in this order: shape and cut, measurements. The first feature describes the shape of the stone and the cutting style, such as emerald or pear. After that, you can see the physical dimensions measured to the nearest hundredth of a millimeter.

3. The Four Cs

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 rating is based on an assessment for the lack of color in the diamond. Color grades start from D to Z and fancy colors are assigned if a diamond lies outside the Z color rating.

The clarity grade is determined by a skilled gemologist who examines the stone under 10X.

If the diamond is a standard 57 facets round brilliant, all reports dated after 2006 will include a cut grade. Cut grade is assigned based on a scale of excellent to poor a GIA report. This is an essential quality to look out for because it determines how much the diamond will sparkle and shine.

While the majority of the gemological labs don’t assign a cut grade for fancy shapes like the heart, marquise or pear, they might use a different formatting to present cut data and information.

With that said, each of these Cs is important consideration for decision making and we 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 called polish and symmetry. The ratings given here will affect the diamond’s appeal and cut grading as they play a role in determining the diamond’s brilliance and luster.

Polish specifies the smoothness of the stone’s surface and the best rating for polish shows that the cutter took exceptional care in crafting the gem. Symmetry is the comparison of how the stone’s facets are aligned in relation with one another. For more information on polish and symmetry, click here.

The next feature you can find in this section is the fluorescence description. Fluorescence is the observation of the type of color and intensity a diamond displays when exposed to ultraviolet (UV) light.

Is fluorescence a friend or a foe? This is perhaps one of the most misunderstood properties in the grading report and consumers are frequently fed with inaccurate information about fluorescence. We addressed those questions here and I strongly encourage you to check the article out if you intend to buy a diamond with fluorescence.

Under the “Other Comments” section, any other information that the stone has. For example, laser inscriptions, additional information to help identify the stone or other clarity characteristics that are too complicated to be placed on the inclusion plot are listed here. While most the comments made here are benign, some may raise a red flag for attention. This article takes an in-depth look at the notes made under “Other Comments”.

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 “birthmarks” found in the diamond. Be careful when reading the important symbols identifying the type of flaws.

Diamond inclusions and flaws can come in vary types and shapes. Blemishes are marked in green color while inclusions are marked in red. If you are interested to see how how some of the more commonly found clarity characteristics look like, head over to this page here that shows clarity characteristics with 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 (finish). Do note that the proportions given for fancy shapes usually omit the values for crown and pavilion angles.

On the proportions diagram, the presence of a culet is also indicated. Generally speaking, we don’t want to see culet sizes that are bigger than small as it can cause the appearance of the diamond to detract.

Girdle: This part of your diamond grading report describes the dividing line between the crown (top part of the stone) and the pavilion (bottom part of the stone). A faceted girdle can sometimes improve the value of your diamond.

the complete folded certification

6. Security Features And Authenticity Marks

Finally, you should also look out for security features on the report. These features can help prove the authenticity of the document and may include a hologram or a universal product code. Most labs provide an online verification service where you can plug in the report number to do an instant verification. We have compiled a useful list here for your convenience.

A Video Summary of Reading a Diamond Certificate


Other Indepth Articles on the Different Aspects of Lab Reports Below:

  • Depth And Table Values in the Proportions Plot
    These are the 2 most important values in a diamond’s proportion plot that you need to know. However, these 2 values by themselves aren’t enough to tell you a stone looks like physically.
  • Importance of a Diamond’s Girdle Thickness
    The diamond’s outermost circumference is called the girdle and can range from different values depending on how well the diamond is cut. What kind of girdle thickness is optimal? Is the finishing on the girdle of importance?
  • HRD Diamond Certification Lab – Are They Reliable?
    Besides GIA, AGS and EGL being the major players in grading diamonds, one of the more commonly found lab which is very popular in Europe is the HRD lab. Is a certificate from HRD worth any good? We find out in this review.

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  1. Bill-
    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. 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: http://beyond4cs.com/grading/girdle-thickness/does-finishing-matter/

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