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    GIA vs AGS Graded Diamonds – Which Gemological Laboratory is the Best?

    This is an excerpt from an email which I received from a client asking for me to help him select diamonds for a three stone ring: “Each stone to be round brilliant cut, at least F color, at least VS2, triple excellent for cut/polish/symmetry and fluorescence to not be stronger than medium, and preferably all certified with GIA. I haven’t really had much to do with AGS so not sure about that lab, but you seem to hold them in high esteem so may consider them too.” — Ken L.  Based on this comment, I thought it might be helpful to share some insight about the two gemological laboratories.

    A Brief History of the GIA and AGS Laboratories:

    The Gemological Institute of America (GIA) was started in 1931 by Robert M. Shipley, a successful retail jeweler who wanted to create a uniform standard of grading diamonds and colored gems, so that the public could have greater trust in the industry. Shortly thereafter, Shipley launched the American Gem Society (AGS) in 1934, to unite retail jewelers around a common sense of morals and ethics by which they would conduct themselves with the public.

    The GIA Laboratory issued its first diamond grading report in 1955, and they quickly became the industry standard for diamond grading. Since the GIA was the only premier gemological laboratory for many, many years, it enjoys a level of market recognition which rivals that of industry giant Tiffany & Co., but both have their challenges trying to retain their hold on the market.

    The heavy weight contender for the GIA is the American Gem Society Laboratory (AGSL) which was launched by the American Gem Society in 1996, after the sister organizations suffered a bit of a falling out over whether an overall cut grade, including crown and pavilion angle measurements, should be added to GIA diamond grading reports… At the time, I remember thinking how great it would be to have that information added to GIA diamond grading reports, because we were selling diamonds that would benefit from the documentation of that type of information.

    But the majority of the diamond industry flipped out, I mean, they completely lost their minds, because  they did not specialize in “diamonds of exceptional make” as we called them at the time, and they realized that making this type of detailed information available to the public, was the equivalent of tearing the lid off of Pandora’s box, forever… and they were right!

    How the AGSL Changed the Diamond Industry Forever:

    So when all of this went down, Peter Yantzer, who is the current director of the American Gem Society Laboratory, was the lab director for the Gemological Institute of America. Peter, who I consider to be a personal friend, and thus who I will refer to as Peter in this article, had been trying to get the board of directors at the GIA, to approve the addition of an overall cut grade and the crown / pavilion angle measurements to their diamond grading reports.

    As I recall, the proposal was initially met with enthusiasm, there were talks of an industry wide boycott by some very large diamond cutting firms who threatened to send all of their diamonds to other, lesser known laboratories such as the European Gemological Laboratory (EGL), the International Gemological Institute (IGI), etc., and so the proposal was rejected.

    But even though the initial proposal was rejected by the talking heads at the GIA, it had caught the interest of the board members of the American Gem Society, and they offered to fund a laboratory for Peter, who promptly opened the American Gem Society Laboratory in 1996.

    Those of us who specialized in diamonds of exceptional make, found it pretty easy to adapt to the new industry standard for diamond grading, which provided an overall cut grade for round brilliant cut diamonds, using a numerical scale ranging from 0 – 10 based on individual grades for polish, symmetry, and proportions, with the overall cut grade of the diamond being equivalent to the lowest score for any parameter of cut quality.

    Creation of the Great Divide within the Diamond Industry:

    While the select few of us who already specialized in Hearts and Arrows Diamonds and other diamonds of exceptional make loved the cut grade system introduced in 1996 by the American Gem Society Laboratory, the majority of the diamond industry was not so fond of it.

    So while we and other online vendors, like [what is now] Brian Gavin Diamonds, High Performance Diamonds, and James Allen, who focused on diamond cut quality and visual performance were promoting it online to all of our customers, the majority of the retail trade was flying the colors of the GIA, and hoping to sink the S.S. AGSL, by either flat out denying the existence of the laboratory, or challenging the validity of their grading practices all together.

    Believe me, nothing was more entertaining at the time, than one of our customers calling us up to tell us that they had just walked out of a jewelry store which promoted themselves as a Member of the American Gem Society, but who purported to only sell diamonds graded by the GIA “because they are more accurate” and who apparently wasn’t even aware that the “society” which they belonged to had even launched a gemological laboratory! Whoops, might be time to crack open a trade magazine, or read your mail!

    The stories got even funnier when our clients would tell us that the “diamond experts” at the store, didn’t have a clue as to what the crown and pavilion angle measurements for the GIA graded diamonds that they were selling, and that the only response that they seemed to have for any questions pertaining to “Hearts and Arrows Diamonds” was that all of that is “smoke and mirrors” and yet they couldn’t provide any insight into how the magic trick was performed (because they’d never seen one).

    Awakening the Sleeping Giant:

    Now June of 2005 is a bit of a blur to me, because that is when my wife Robin committed suicide. Yea sorry, I didn’t see that one coming either, but if you want to know more about it, you can read my article “The Suicide Note” on my personal development coaching blog, I wrote it on the seven year anniversary of her death… but one of the things that I distinctly remember about that time in my life is being amused by the fact that just as the GIA proudly announced that they were adding an overall cut grade, based on the proportions, polish, and symmetry grades of the diamond, the AGSL announced that they were moving beyond proportions based cut grading to focus on a grading platform that revolves around the actual light performance of the diamonds.

    I remember thinking that it took almost a decade for the GIA to acknowledge the importance of cut grade and the effect that the crown and pavilion angles have upon light return, and the AGSL rolls up alongside them and quite literally blows them out of the water by introducing their Angular Spectrum Evaluation Tool (ASET) and in doing so, moved the industry forward light years beyond the proportions based cut grade system which the GIA still employs almost a decade later… That’s right, from my perspective, the industry leader in diamond grading, is running about a decade behind those other guys…

    But which gemological laboratory is more accurate?

    I’ve had my fair share of experience sending diamonds to be graded by both the GIA and the AGS gemological laboratories, and I’ve heard all sorts of theories about how each laboratory grades diamonds differently, more accurately, less accurately, than the other, and I have to tell you, I find them to be comparable in the level of consistency for carat weight, color, clarity, polish, symmetry, proportions, and fluorescence.

    I’ve sent diamonds to both laboratories for side-by-side comparison of the diamond grading reports and feel that they are comparable in their grading standards, which is not really surprising since both laboratories employ GIA Graduate Gemologists as diamond graders, thus the GIA is still setting the standards for diamond grading, since they are the ones teaching people how to grade diamonds.

    Keep in mind that the proportions of a diamond are determined by measuring the diamond using computerized proportions analysis, both the GIA and AGS use Sarin machines to measure their diamonds, but each one uses proprietary software which has been designed by Sarin to suit their individual grading standards for proportions… so there is very little variance between the gemological laboratories with regard to how diamonds are measured.

    But factors such as clarity, color, and fluorescence, are graded by human eyes, which are subject to variance due to a variety of conditions, including the personal vision of each diamond grader… but each laboratory has their own system in place for the accurate determination of clarity, color and fluorescence grading, like having more than one grader look at a stone.

    I have yet to see a discernible difference between the GIA Excellent and AGS Ideal grades for polish and symmetry, to the extent that I consider GIA Excellent to be the equivalent to AGS Ideal for polish and symmetry…

    Differences between GIA Excellent & AGS Ideal:

    The biggest difference in my mind between the GIA Excellent or “GIA 3X” overall cut grade, and the overall cut grade of AGS Ideal-0 lies in the differences between the parameters for the GIA Excellent proportions and the AGS Ideal proportions grading platforms… It seems to me that the parameters for the AGS Ideal-0 proportions grade are a lot tighter than the guidelines for the GIA Excellent proportions grade.

    Round Brilliant Ideal Cut Diamond from James Allen, GIA #16770376To the extent that I often find myself staring at “Cut Grade…….Excellent” line on some GIA diamond grading reports and the proportions outlined on the proportions diagram and wondering how that determination was made.

    Admittedly, I also disagree with some of the proportion combinations which can obtain an AGS Ideal-0 proportions grade on the outlying regions of the proportions charts used by the AGSL, but it is a bit less of a stretch, and I am known to be a bit of a diamond snob.

    For instance, take the measurements of this 1.67 carat, F-color, VS-2 clarity, GIA 3X diamond from James Allen, pictured to the left, it has a total depth of 61.4% with a table diameter of 56% and a crown angle of 35.5 degrees which is offset by a pavilion angle of 41.0 degrees with a thin to medium, faceted girdle. The overall cut grade is GIA Excellent (proportions, polish, symmetry).

    Now I can tell you from experience that the combination of the 43.5% pavilion depth is a problem, because that happens to be the critical tipping point where I find that light begins not to strike fully off of the pavilion facets; and the effect of the 85% lower girdle facets is going to be that the sparkle is extremely small in size, which will affect the ability of our human eyes (as opposed to a camera lens) to disperse the flashes of white light into colored sparkle / fire, and thus this diamond is likely to perform best in pin-fire type lighting conditions, e.g. candle light and halogen jewelry store lighting, but not so well under normal lighting.

    AGSL Proportions Chart for 56% Table Diameter:

    AGS Proportions Chart for Round Diamonds with a 56 percent table diameterThe picture to the left is a portion of the proportions grading chart published by the American Gem Society Laboratory in 2008 for round brilliant cut diamonds. To use it, simply go to the chart designed to be used for the table diameter of the diamond being considered, which is 56% in this case, then cross reference the measurements for crown and pavilion angle.

    In this particular instance, the crown angle of the diamond is 35.5 degrees and the pavilion angle is 41.0 degrees, I cropped down the image on the right and bottom sides, so that the cross section where the two measurements meet on the chart, is the red box that appears in the lower right corner of the graph as indicated by the red arrow.

    On the AGSL proportions scale published in 2008, the color pink is used to indicate AGS Ideal-0 proportions; AGS-1 Excellent is represented by the color red; AGS-2 Very Good is indicated by the color gold; AGS-3 Good is indicated by the color yellow. So the proportions rating of this diamond would be AGS-1 Excellent, and thus in this particular bout of the GIA vs AGS, the overall cut grade of GIA Excellent is not equivalent to the AGS Ideal-0 cut rating, but keep in mind that this does not take the crown height or pavilion depth measurements into account, and thus it reveals only part of the picture!

    How to Read an ASET image on an AGS DQD:

    AGS DQD for Brian Gavin Blue Fluorescent Diamond, AGS #104064812027But the differences between the highest overall cut grades offered by the AGS and GIA gemological laboratories, do not end with the parameters of their proportions grade. The biggest difference between the GIA and AGSL is that the AGSL employs the use of their Angular Spectrum Evaluation Tool (ASET) on their Proprietary Light Performance grading platform.

    The diamond grading report for this 1.512 carat, F-color, VS-2 clarity, from the Brian Gavin Blue collection, pictured to the left, shows how the diamond looks as seen through the ASET, as seen here in red, green, and blue. All of that red that is visible in the image, represents the brightness of the diamond, and light green indicates areas that are less bright, with the blue arrows representing the areas of the diamond that are reflecting the camera lens back towards the viewer.

    Notice how symmetrical the patterns are… The symmetry of the patterns represented by each color, are an indication of the precision of optical symmetry that this diamond has been cut to, and this will have a direct affect upon the sparkle factor exhibited by this diamond.

    The higher the degree of optical symmetry, the more contrast that is going to be created within the diamond, thus the more vivid it is going to appear, especially since this Brian Gavin Signature diamond is cut with lower girdle facets in the range of 75 – 78% which is going to create larger sparkle, that is bolder, brighter, and more vivid!

    Now before you get too caught up in all of those red and green sections portrayed on the ASET image, I should point out that there will be many times when the two colors will meet or blend in a particular section of the diamond, this is because the edge of the range for both red and green, are shared by both colors when the diamond is gathering light from within the room from the vantage point of 45° so don’t freak out if you see both red and green somewhere like the center of the table facet, which is facing up as all green in this particular image… it’s perfectly normal.

    It’s No Secret that I prefer the AGSL for Diamond Grading:

    All right, I have nothing but respect for the GIA and their Gem Trade Laboratory, their contribution to the diamond industry is undeniable, and I find their grading practices to be consistent, however I personally prefer the additional insight provided by the addition of the ASET results on the AGSL Proprietary Light Performance Diamond Quality Document.

    The reality is that with all other factors being essentially equal, e.g. if I were considering two diamonds, one graded by the GIA and the other graded by the AGSL, and both have the same carat weight, clarity, color, fluorescence, polish rating, symmetry rating, table diameter, total depth, crown angle, pavilion angle, girdle thickness, etc., that additional information such as the ASET image and other reflector scope images, such as the Ideal Scope and Hearts & Arrows Scope images, enable me to take the optical symmetry of the diamond into account.

    And a lot of vendors are not equipped to provide these images for their customers, so if it so happens that the ASET image is provided on the Diamond Quality Document issued by the AGS Laboratory, it just makes my job that much easier… But this does not mean that you should only consider diamonds graded by the AGSL, because there are a lot of exceptional options to be found which have been graded by the GIA with an overall cut grade of GIA Excellent, or what is commonly referred to as “GIA 3X” if you know what to look for, and what to ask for…

    When looking for round brilliant cut diamonds, I recommend limiting your search to diamonds which have been graded with an overall cut grade of AGS Ideal-0 or GIA Excellent, within the following range of proportions:

    Total depth between 59 – 61.8%
    Table diameter between 53 – 57.5% (maybe 58%)
    Crown angle between 34.3 – 34.9 degrees
    Pavilion angle between 40.6 – 40.9 degrees
    Girdle: 0.7% thin to medium, faceted or polished
    Culet: AGS “pointed” or GIA “none” (same thing)

    Now here’s the twist… the parameters that I outline above represent the middle of the spectrum, or “the sweet spot” within the range that the AGSL specified for their zero ideal cut proportions rating, but there are other combinations of crown and pavilion angle that will provide a comparable volume of light return. Rather than get into a really long dialogue about all of the possibilities, just feel free to consider me your Personal Diamond Shopper and send me the details of any diamonds that you’re considering, I’m happy to look over the details for you and make recommendations.

    About the AuthorTodd Gray

    Todd Gray is a professional diamond buyer with 30+ years of trade experience. He loves to teach people how to buy diamonds that exhibit incredible light performance! In addition to writing for Nice Ice, Todd "ghost writes" blogs and educational content for other diamond sites. When Todd isn't chained to a desk, or consulting for the trade, he enjoys Freediving! (that's like scuba diving, but without air tanks)

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