Diamond certificate: your comprehensive guide part 1/2

By Yves Lemay May 20, 20

Diamond characteristics documented in a diamond grading report

Shape and Cutting Style: The diamond shape and cutting style. 


Measurement: Lists the diamond's dimensions in millimeters. 


Carat Weight: The weight of diamond listed to the nearest hundredth of a carat. 


Color Grade: A grading that assesses the degree or absence of color in a diamond. 


Clarity Grade: Clarity grade determined under 10 x magnifications. 


Cut Grade: A grade of cut as determined by a diamond's face-upappearance, design, and craftsmanship. A cut grade is available on round diamonds graded by GIA after Jan. 1, 2006. 


Finish: Grades that represent a diamond's surface and facet placement. 


Polish: Rating the overall smoothness of the diamond's surface. 


Symmetry: Measuring the shape, alignment, and placement of the diamond's facets with one another as well as the evenness of the outline. 


Fluorescence: Color, and strength of color when the diamond is viewed under UV light. 


Comments: A description of additional diamond characteristics not already mentioned in the report. 


Clarity Plot: A map of the approximate size, type, and position of inclusions as viewed under a microscope. 


Proportion Diagram: A map of the diamond's actual proportions. 


Reading a proportion diagram

Proportion diagrams will typically include the following information: 


Depth: The height of a gemstone measured from the culet to the table. 


Table: Located at the top of the diamond, the table is the largest facet of a diamond. 


Girdle: Range of girdle thickness. 


Culet: Appearance, or lack thereof, of the culet facet.


The 5 most respected gemological institutes in the world

The most renowned and trusted gemological grading laboratories are the Gemological Institute of America (GIA), the Hoge Raad voor Diamant (HRD), the American Gemological Society (AGS), the International Gemological Institute (IGI), and the two versions of European Gemological Laboratory (EGL International and EGL USA). 


From these five laboratories, the three that set the standard are the GIA, AGS & HRD. 


The GIA is widely regarded as the most reputable and recognized grading laboratory in the world, with the strictest standards. 


Founded by the creator of the GIA, The American Gemological Society (AGS) is a newer certification and markets itself around the fact that it offers an Ideal cut grade, which is one higher than the Excellent from GIA and is as strict as GIA in every respect. 


The Hoge Raad Voor Diamant (HRD) or Diamond High Council is almost as renowned worldwide as GIA but not as popular, and it is 95% as strict in its grading. 


Even though these are the five leading international diamond certification organizations, their grading criteria do vary and are not equally strict. 


Please be aware of the differences when choosing your diamond. 


All the certificates differ slightly in layout, terminology, and grading systems, with some including diagrams and symmetry or proportion grading and others being simpler. 


A color grade may differ in up to two grades from one certificate to another. 


Yet, this is not always reflected in the price, so beyond understanding how color or clarity grades work, it is essential to know how to interpret and compare them. 


Laser inscribed validation

With the five leading diamond certification organizations, recent measure to protect the consumer has resulted in certificated diamonds being laser inscribed, usually on the diamond’s girdle, which gives confidence the diamond purchased is the diamond received. 


The laser inscription can be easily verified with a magnification loop. 


See below for an example of diamonds inscribed by GIA (figure 1) and EGL (figure 2).  


gia certificate and laser inscription yves lemay jewelry
egl certificate and laser inscription yves lemay jewelry

Certificates comparisons

The most renowned and trusted gemological grading laboratories are the Gemological Institute of America (GIA), the Hoge Raad voor Diamant (HRD), the American Gemological Society (AGS), the International Gemological Institute (IGI), and the two versions of European Gemological Laboratory (EGL International and EGL USA). 


From these five laboratories, the three that set the standard are the GIA, AGS & HRD. 


The GIA is widely regarded as the most reputable and recognized grading laboratory in the world, with the strictest standards. 


Founded by the creator of the GIA, The American Gemological Society (AGS) is a newer certification and markets itself around the fact that it offers an Ideal cut grade, which is one higher than the Excellent from GIA and is as strict as GIA in every respect. 


The Hoge Raad Voor Diamant (HRD) or Diamond High Council is almost as renowned worldwide as GIA but not as popular, and it is 95% as strict in its grading. 


Even though these are the five leading international diamond certification organizations, their grading criteria do vary and are not equally strict. 


Please be aware of the differences when choosing your diamond. 


All the certificates differ slightly in layout, terminology, and grading systems, with some including diagrams and symmetry or proportion grading and others being simpler. 


However, the two main grading aspects to consider when comparing certificates are color and clarity, for their evaluations largely determine the price of a diamond, and yet they are not consistently graded across the board. 


A color grade may differ in up to two grades from one certificate to another. 


Yet, this is not always reflected in the price, so beyond understanding how color or clarity grades work, it is essential to know how to interpret and compare them. 


Certificates comparisons for color

Overall, the GIA tends to be the strictest on color grades, and out of the other laboratories, HRD and AGS are the two that most closely adhere to the standards set out by the GIA. 


IGI and EGL USA tend to give one color grade higher than GIA and EGL up to 2 color grades higher. 


So an F color stone on a GIA certificate would most likely be the same on HRD and AGS, an E on IGI or EGL USA, and a D on EGL. 

Please refer to the table below for a more detailed comparison*


certificate comparison for color between different diamond grading labs yves lemay jewelry

*Note: Although not published anywhere, these differences are generally accepted within the diamond trade as correct.


Certificates comparisons for clarity

Again, with clarity, the GIA is said to be the strictest, giving at least one grade lower than all other laboratories. 


The HRD adds its clarity grade to the traditional scale, terming all stones with impurities invisible with a 10x loupe as “Loupe Clean.” 


Because of this extra category, stones grades as IF or FL by the HRD would only receive a VVS1 from the GIA. 


The same applies to IGI, EGL, and EGL USA, which would make all grade between one and two clarity grades higher than the GIA. 


Please refer to the table below for more detailed comparisons*. 


certificate comparison for clarity between different diamond grading labs yves lemay jewelry

*Note: Although not published anywhere, these differences are generally accepted within the diamond trade as correct.


Other differences between certificates

The main other differences between the certificates lie in the differences between GIA, HRD, and AGS. GIA gives separate grading for symmetry and polish, which the HRD groups together under the heading of “finish.” 


HRD also includes one clarity grade termed “Loupe Clean,” which is not offered by the GIA. 


The AGS provides more information on the cut grade and offers one grade higher than the traditional poor-to-excellent scale of GIA, called “ideal cut,” as well as a number scale from 0-10 on which to grade diamond cut. 


Individual grading laboratories and certificates

There are many diamond grading laboratories around the world, all of which produce their grading reports according to their standards and, in some cases, employ their own

 terminology. 


As certificates play a large part in determining the value of diamonds, it is crucial to understand the different grading systems and how they compare with each other.


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