The American Gem Society Laboratory (AGSL) and the Gemological Institute of America (GIA) Gem Trade Laboratory (GIA-GTL) set the standard by which all other gemological laboratories are compared, but are the two gemological laboratories truly equal when it comes to the standards by which they grade diamonds? Both the AGSL and the GIA are Heavy Weight Contenders which command the highest respect throughout the industry, and they are extremely well matched in terms of the grading standards which they use to grade diamond carat weight, clarity, color, fluorescence, polish and symmetry.
The Gemological Institute of America (GIA) was founded in 1931 by Robert M. Shipley, who was named Man of the Century by JCK Magazine in the December 1999 issue. In terms of his contribution to the gemological community, I wholeheartedly agree with JCK’s award of this prestigious title because it is difficult to imagine the diamond and gemological business without thinking of ways that it has been affected by the influence of Robert Shipley and the Gemological Institute of America. Photo courtesy of the Gemological Institute of America.
As stated in the article “Consider his accomplishments: He introduced gemological training to the United States and established the first gemological school, the first research laboratory, and the first professional gemology journal in North America. He pioneered the creation and use of gemological instruments. He founded the first professional society of jewelers in North America and organized the first national educational conclaves of jeweler/gemologists. He instituted industry-wide standards for grading and nomenclature. He even helped create the “four Cs” of diamond buying.”
By the way, that reference to “the first professional society of jewelers in North America” is a reference to the American Gem Society, which was started by Shipley in 1934. The intent behind the GIA was to provide jewelers in North America with gemological education, and the AGS was created to provide a foundation of morals and ethics for responsible jewelers to follow.
According to the article by JCK Magazine “Those GIA courses and the early AGS conclaves stitched together a national community of jeweler-gemologists, unifying the industry at the grass roots.” When I first got started in the diamond back in October of 1985 (oy vey, has it been almost thirty years already?) it was explained to me that the Gemological Institute of America and the American Gem Society were “sister organizations” founded by Robert M. Shipley to create a uniform grading system for diamonds and colored gems that was used world wide, and a foundation of ethics for the industry to follow. My hat goes off to Robert M. Shipley, he was a major contributor to the trade that I enjoy, and I use the information taught to me by the GIA almost every day… so thank you.
Everything seemed to be going fine between the two sister organizations until the mid-1990’s when GIA Lab Director Peter Yantzer suggested to the GIA Board of Directors that additional criteria be added to the format of the diamond grading reports issued by the Gemological Institute of America Gem Trade Laboratory (GIA-GTL) specifically crown and pavilion measurements, representing the top and bottom halves of a diamond. As I recall the suggestion to add crown and pavilion measurements to the GIA diamond grading report format was initially accepted by the GIA Board of Directors, but later rejected due to pressure from various diamond cutters who threatened to boycott the laboratory if they insisted on providing the public with that sort of detail.
Now I’m not suggesting that certain elements of the diamond business preferred to keep the diamond buying public in the dark and guessing about the details of diamond cut quality… No, I’m just going to come right out and say it. The majority of the diamond industry seems to prefer customers who are not brilliant, pun intended. Keep in mind that all of this was occurring at a time when the world was just beginning to wrap its mind around the power of the internet… the diamond industry was losing its mind, and more than fifty members of a diamond trade network known as Polygon had filed a lawsuit against us DBA Nice Ice and Treasures by R.J. for “disclosure of proprietary information to the public” and “disparagement of an entire industry” — Hey, I’m rather proud of myself for that last part “the entire industry” = impressive. If only I could find a picture of a dog licking it’s butt, I could show you what those fifty jewelers looked like after the Law Firm of Orrick, Herrington & Sutcliffe sank their teeth into them. How do you spell R-E-T-R-E-A-T?!?! You’ve got to love the First Amendment, which provides protection of free speech, freedom of expression, and specific protection for satirical wit. Ahem.
Anyway the original diamond grading report format issued by the Gemological Institute of America Gem Trade Laboratory provided very basic details about the proportions of a diamond, such as the outside diameter and depth measurements, along with the total depth, table diameter measurements, girdle thickness and culet size. Critical data such as the crown angle, crown height, pavilion angle, and pavilion depth measurements were not provided. There would have been no way for you to determine how the weight of the diamond was distributed between the upper and lower halves of the diamond, this “diamond grading report” format left a lot to be desired, and I’m not even sure that it should have been referred to as a report since critical data was omitted, intentionally or not.
At some point the Board of Directors for the American Gem Society elected to offer Peter Yantzer the opportunity and funding to open a gemological laboratory at their facility in Las Vegas, Nevada and the rest is history. The American Gem Society Laboratory opened it’s doors in 1996.
People frequently ask me whether the American Gem Society Laboratory grades as consistently as the GIA Gem Trade Laboratory… Whether the AGSL is as strict as the GIA. Whether the GIA is stricter on color or clarity grading than the AGSL. Whether the AGSL is less strict on color or clarity grading. Which diamond grading laboratory do I prefer, etc. and the the answer always seems to surprise them.
Are you sitting down? Because here it comes… This is a Diamond Quality Document issued by the American Gem Society Laboratory on December 09, 2013 for this 1.255 carat, D-color, Internally Flawless clarity, Brian Gavin Signature round hearts and arrows cut diamond which has been sold:
According to the American Gem Society Laboratory this 1.255 carat, D-color, Internally Flawless clarity, Brian Gavin Signature round hearts and arrows cut diamond measured 6.88 – 6.90 x 4.27 millimeters and had a total depth of 61.9% with a table diameter of 56.7% and a crown angle of 35.0 degrees and a crown height of 15.2% with a pavilion angle of 40.7 degrees and a pavilion depth of 43% with lower girdle facets that measure 76% in length and star facets that measure 53% in length with a thin to medium, faceted girdle and a pointed culet.
The same diamond was submitted to the GIA Gem Trade Laboratory a little more than two months later on February 27, 2015 at which time it was determined to be a round brilliant cut diamond weighing 1.25 carats, D-color, Internally Flawless clarity, with an overall cut grade of GIA Excellent, GIA diamond grading report number 2145936424. Here is a copy of the GIA diamond grading report:
If we combine the diamond details from the two diamond grading reports issued by the American Gem Society Laboratory and the Gemological Institute of America into a spread sheet, it looks like this:
Notice that there are slight differences between the format of the data provided by the AGSL and the GIA, and while the measurements are similar, they are also dramatically different. Why are the measurements so different if the diamond graded by both laboratories is the same Brian Gavin Signature round diamond? The answer is remarkably simple. The GIA rounds off the measurements for crown, pavilion, lower girdle facet length, and the star facet length to the nearest half a percent or half a degree, whichever is appropriate for that section; while the AGSL reports the actual measurements without rounding them off.
Thus the crown height of 15.2% reported by the AGSL becomes a crown height of 15% as reported by the GIA. The lower girdle facet length of 76% reported by the AGSL, gets rounded down to 75% by the GIA because it falls below 77.4% but would have been rounded up to 80% if it were 77.5% or higher. This practice of rounding off measurement by the GIA makes it practically impossible to estimate the visual performance of a GIA Excellent cut diamond based upon the data provided on the GIA diamond grading report, after all the data provided for lower girdle facet length has a variance of approximately 2.5% in either direction of the stated value.
Notice how the star facet length of 53% was rounded up to 55% and be aware that it would have been rounded down to 50% by the GIA Laboratory if it had measured 52.4% instead of 53%. Here again the measurement provided has a potential variance of as much as 2.5% and thus it is practically useless in terms of assisting us with the diamond selection process.
Now some people will tell you that this variance is acceptable because these measurements represent the average of eight individual measurements taken by section, and while that is true, they are missing the point. Both the AGSL and the GIA use computerized proportions analysis machines to measure diamonds, and those machines report the average of the eight measurements that are taken for each section of the diamond, thus the lower girdle facet measurement of 76% represents the average of eight individual measurements. But then the GIA takes that average measurement and rounds it off to the nearest half a percent or half a degree, whichever is appropriate for that measurement!
Another thing to be aware of is that the GIA and AGS measure the lower facets differently, dramatically differently! The AGS measures lower girdle length by height, this is the same as how the DiamCalc software designed by the University of Moscow does it. While the GIA measures lower girdle length by radius, because that way independent gemologists can measure it using a table gauge if the diamond is mounted, or if they do not have access to computerized proportions analysis. The difference between how the AGSL and GIA-GTL determine the lower girdle facet measurements can create confusion among the public who assumes the measurements are determined the same way when actually the difference in how they are measured looks more like this:
Got a headache yet? I don’t blame you, and it might just get a little bit worse before we’re finished, but at least you’ll have a better understanding of the reasons why I prefer the ASET based Light Performance grading platform of the American Gem Society Laboratory.
Get a load of these charts created by Bruce Harding and Jason Quick that show the relationship; between the GIA Lower Girdle Radius measurements and the Lower Girdle Height measurements used by AGS and DiamCalc:[separator]
Pay particular attention to the measurements between the range of 75 – 80% which is the range that I recommend in the article 15 Seconds to Diamond Buying Success, which is intended to be used with diamonds graded by the American Gem Society Laboratory, which is my gem lab of choice since I can reliably use the measurements provided on the diamond quality document (DQD) to estimate the visual performance of the diamond.
Note that the proportions of a diamond are only one piece of the puzzle, and that reflector scope images like those provided for all Brian Gavin Signature diamonds are necessary to judge the degree of optical precision that the diamond has been cut to. Optical precision refers to the consistency of facet size, shape, and the alignment or indexing of the facets as they were polished on to the surface of the diamond from the perspective of 360 degree alignment. Here are the reflector scope images for the 1.255 carat, D-color, Internally Flawless, Brian Gavin Signature diamond that we’ve been discussing thus far:
This series of reflector scope images provided for the 1.255 carat, D-color, Internally Flawless, Brian Gavin Signature diamond and which is provided for all Brian Gavin Signature round diamonds, consists of an ASET Scope image (left), an Ideal Scope image (center), and a Hearts & Arrows scope image (right) all of which are required to comprehensively evaluate diamond cut quality.
Only the American Gem Society Laboratory (AGSL) uses Angular Spectrum Evaluation Technology (ASET) to measure the brightness of diamonds, and to determine how effectively a diamond is making use of the light which is available to it from within the room. The results of the ASET scan are provided on AGS Light Performance Diamond Quality documents, and responsible vendors like Brian Gavin Diamonds, High Performance Diamonds, and Victor Canera provide them on the diamond details pages for their round hearts and arrows cut diamonds.
These three vendors also routinely provide Ideal Scope images for all their round brilliant hearts and arrows cut diamonds, along with most other diamond shapes that they sell. We use the Ideal Scope to determine the extent to which a diamond is leaking light due to the combined effect created by the proportions and facet structure of the diamond.
These three vendors also specialize in Hearts and Arrows quality diamonds, graded by the American Gem Society Laboratory with an overall cut grade of AGS Ideal-0 and thus they provide Hearts & Arrows scope images for their hearts and arrows diamonds, so that you can verify that they have been cut to the highest degree of optical precision possible.
The details pages for James Allen True Hearts diamonds feature an image of the hearts pattern and an Ideal Scope image, but do not provide an ASET image, and the diamonds are graded by either the AGSL or GIA gemological laboratories. I’ve noticed that a lot of them are graded by the AGSL on the grading platform that does not provide an ASET image, which seems a bit suspect to me since it is a step down from the ASET based Light Performance grading platform.
Right about now, you might be wondering whether GIA Excellent cut diamonds are worth the money since the American Gem Society Laboratory appears to be winning the bout when it comes to grading diamond cut quality. Clearly the AGS Laboratory provides a more in-depth diamond grading report, complete with an ASET image and measurements that better reflect the actual proportions of the diamonds being graded.
However there are some exceptional diamonds being submitted to the GIA Laboratory for grading, you just have to do more legwork to find them, because you’re going to have to ask the vendor to provide you with reflector scope images and a manufacturer’s Sarin report, which most of them are not going to be able to provide. Thus you’re likely to find yourself back at square one buying a GIA Excellent cut diamond “by the numbers” with the understanding that there can be more than two percent wiggle room in the measurements stated on the diamond grading report.
I invite you to take advantage of my free Diamond Concierge Service if you would like assistance finding the diamond of your dreams, and/or looking over the details for a diamond which you may be considering, whether the diamond is offered by an online vendor that I work with, or your local retail jeweler. Simply send me the details about the diamond you are looking for, or send me a link to the diamond details page, or the GIA or AGSL diamond grading report number along with the carat weight, color, and clarity of the diamond.
If you want my help searching for a diamond, please provide me with the shape of the diamond you seek, along with the range of carat weight, color, fluorescence, clarity and price that you are working with. Thank you.