Categories: Grading Practices

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.

To 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:

The 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:

But 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.

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)

@NiceIceDiamonds

Professional diamond buyer with 30+ years trade experience in the niche of super ideal cut diamonds. In my free time, I enjoy freediving & photography.
The incredible #story behind the Sirisha diamond necklace by @BrianGavin 71 #Diamonds cut to order #Amazinghttps://t.co/dHOo1T99xT - 2 years ago
Todd 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)

View Comments

  • Hi Todd,
    Very good information and learning a lot more about what to look for in a diamond. Thinking about going forward on this diamond and what to know if this worth the price that it’s offered at $2450

    AGS#: 104090205017
    Round Brilliant 5.33-5.37x3.29mm
    l/w ratio: 1.01
    Cut grade AGS Ideal
    .578 carat
    Table: 56.5
    Depth: 61.5
    Crown angle: 34
    Crown depth: 14.7%
    Pav angle: 40.8
    Pav depth: 43.1%
    Lower Girdle Length: 77%....Think this is correct
    Star Length: 49%..... Think this is correct
    The above two numbers are on the AGS report located on the diamond assuming they mean lower girdle length and star length
    Faceted 1.5%-4.4%
    Culet: Pointed
    Fluorescence Negligible……not sure what this means???
    Polish and symmetry ideal
    F VVS2
    Holloway score 1.1

    Is there any other concerns you have based on the limited information. I am looking at quality with a lot of “fire” vs. the size of the stone

    Thanks for your time!!
    Dave

    • Happy new year Dave! All right, so you're looking at AGS#104090205017 which is a 0.578 carat, F-color, VVS-2 clarity, AGS Ideal-0 cut round diamond with a total depth of 61.5% and a table diameter of 56.5% and a pavilion angle of 40.8 degrees, which is offset by a 34.0 degree crown angle. I looked up the diamond grading report and unfortunately it is in the format which does not provide an ASET Scope image - so I don't have a way to judge the degree of brightness, nor determine how evenly light is reflecting throughout the diamond. By chance, does the vendor have those images? Ideally, I'd like to see an ASET Scope, Ideal Scope, and Hearts & Arrows scope image.

      As far as predicting light return "by the numbers" we can assume that the 40.8 degree pavilion angle is going to provide a high volume of light return. The 34.0 degree crown angle is a bit shallower than my preferred range which is between 34.3 - 35.0 degrees, and this is likely to produce a hint more brilliance (white sparkle) as opposed to producing the virtual balance of brilliance and dispersion (colored sparkle / fire) that tends to be provided by that 34.3 - 35.0 degree range. The 75% lower girdle facet length should ensure that the sparkle is larger in size and bolder in appearance.

      "Negligible fluorescence" on the AGS grading scale is comparable to "none" on the GIA grading scale. The AGSL prefers the word "negligible" which means "not enough to measure" as opposed to "none" because the reality is that there always seems to be "some fluorescence" even when there appears to be none. Don't get too caught up in it, fluorescence almost always helps a diamond look better.

      You are correct that the 49% measurement referenced on the plotting diagram is the star facet length, and the 75% is the lower girdle facet length; both measurements are well within my preferred range. Feel free to email me directly at diamonds[insert at symbol here]niceice.com if you have additional questions or want to forward those reflector scope images to me.

      -- Todd

  • Hi Todd,

    Thanks for providing so much info. It really helps when making such a big decision. I was wondering if I could trouble you in getting your thoughts on the following.

    AGS#: 1195669929
    Round Brilliant 7.43-7.46-4.53mm
    Cut grade: GIA Excellent
    Table: 60.0%
    Depth: 60.9%
    Crown angle: 34.0
    Crown depth: 13.5%
    Pav angle: 41.2
    Pav depth: 43.5%
    Fluorescence: None
    Polish and symmetry: Excellent
    F VS2

    I was just wondering if you had any thoughts of the stone, how the light would look, the inclusions etc? To me the inclusions seem to be clustered around the one area but I am hoping a setting (I was thinking North South East West setting) would "cover" most of it anyway.

    Thank you for your help in advance!

    Jon

    • Hi Jon,

      Thank you for your inquiry. I want to direct you to the listing for the 1.54 carat, F-color, VS-2 clarity, GIA Excellent cut round on Enchanted Diamonds, because the listing provides a clarity photograph which will help illustrate my points.

      The proportions of this diamond are beyond my preferred range which is outlined in 15 Seconds to Diamond Buying Success. The first thing I notice when I look at the diamond clarity photograph, is how the middle of the table facet appears to be pulling inward from the edges towards the middle. It's kind of a black hole type of optical effect which is being created by the larger 60% table facet and the steep pavilion depth.

      I want to draw your attention to the medium density patches of brown light reflecting under the table facet in the relative four o'clock and eight o'clock positions. The fact that both sides of the table facet are darker in those opposing sections is an indication that the degree of optical precision is off in those areas. We know this because the optics of a diamond are such, that the light reflecting from each of those locations is actually coming from the opposite side of the diamond. There is a diagram provided within the article Creation of Hearts and Arrows patterns that demonstrates this concept.

      I'm certain that if we were able to obtain an image of the "hearts pattern" for this diamond, that there would be a significant amount of extra space around each of the hearts in the four o'clock and eight o'clock position and that the hearts would vary in size and shape. Because that is what creates the optical effect that we're seeing here within this diamond. It is also a contributing factor to the moderate obstruction visible under the table facet at the base of the arrows pattern.

      Another factor which is contributing to both the dark areas and the degree of obstruction that is visible under the table facet, is the combination of the 41.2 degree pavilion angle and the 43.5% pavilion depth. In my 30+ years of experience buying diamonds for the trade, I've noticed that "the critical tipping point" where light begins not to strike fully off the pavilion facets is 43.5% and anything beyond that is definitely going to impact the volume of light return. For optimum light return, I recommend focusing on diamonds with a pavilion angle between 40.6 - 40.9 degrees. Obviously you want to keep the pavilion depth below 43.5% in conjunction with that.

      The slightly shallow crown height of 13.5% combined with the 34.0 degree crown angle is likely to produce a higher volume of brilliance (white sparkle) as opposed to the virtual balance of brilliance and dispersion (colored sparkle) that tends to be created by a crown angle between 34.3 - 35.0 degrees. This however does not impact the volume of light return, but rather simply tilts the balance of brilliance and dispersion in one direction or the other. For instance, if you prefer a diamond that exhibits more dispersion (colored sparkle / fire) then you might prefer a slightly steeper crown angle, such as 35.5 degrees combined with a crown height of 15.5% but no steeper! Because when you go beyond that, then it's possible that the diamond will not perform well under the diffused light that we live and work under in this modern age... However that diamond with a 36 degree crown angle and 16% crown height is likely to look spectacular under the pin-fire lighting conditions relied upon by most retail jewelry stores. (Oh, I get it!)

      Now the thing to realize is that I'm not telling you not to buy this diamond. I'm simply breaking it down by the numbers and telling you what I see in terms of how light is reflecting throughout the diamond, due to a combination of proportions and optical precision. My goal in doing so is simply to provide you with the insight to make a more informed decision. This diamond might be perfectly fine for your needs, or you might prefer something with better proportions and a higher degree of optical precision. There is no right and wrong, there is simply better understanding. I'm happy to help you search for additional options if you want to take advantage of my free Diamond Concierge Service. Just drop me a note and let me know the range of carat weight, color, clarity and price that you are open to considering.

      -- Todd

  • Thanks Todd.

    The below was very useful. I was then wondering if you had any thoughts on 6215565150.
    Most of the dimensions fall within your figures except for the crown angle and a bit concerned that it's not within the AGSL proportions "Ideal" cut section of the chart..
    I also haven't seen a clarity photograph or reflector scope images so any thoughts on this too would be very greatly appreciated.

    Thanks so much.

    • Hi Jon,

      Thanks for taking the time to reach out to me for advice. GIA #6215565150 is a 1.50 carat, F-color, VS-2 clarity, GIA Excellent cut round diamond. It is still listed in the MLS that we use to trade diamonds globally, unfortunately there are not any images provided. It was worth a shot! I can find images for virtual diamonds about 60% of the time.

      As you've noted, the crown angle of 33 degrees is just outside the range specified for the zero ideal cut proportions rating by the AGS Laboratory for round diamonds with a 57% table diameter and a 40.8 degree pavilion angle. It is also important to remember that the measurements that appear on an AGS Diamond Quality Document (DQD) represent the average of eight individual measurements taken per section. While the GIA takes that average measurement and then further rounds it off to the nearest half a degree or half a percent! So there is more wiggle room to account for with diamonds graded by the GIA.

      Assuming that the crown angle is actually 33 degrees, then it's likely that this diamond will produce a high volume of light return (due to the 40.8 degree pavilion angle) but will exhibit more brilliance (white sparkle) due to the shallower crown angle / height. There might also be some light leakage created by the shallower crown section, but we have no way of determining that without an ASET Scope, Ideal Scope and Hearts & Arrows scope image. When I run the diamond grading report number for this diamond through the Enchanted Diamonds Cut Score Calculator, they give it a cut score of 94.4% out of a possible 100% for the reasons I've explained.

      This might be a good option if you happen to prefer diamonds that exhibit more brilliance, as opposed to the virtual balance of brilliance and dispersion created by a crown angle between 34.3 - 35.0 degrees. But I'd definitely want to see some photographs of the diamond before purchasing it if you're shopping online. Feel free to email them to me if you get them via diamonds[insert at symbol here]niceice.com or send me a link. If you're buying the diamond in-person, then look for consistency in the way light is reflecting throughout the diamond, especially under the table facet, and be sure to pay attention to the amount of obstruction that may or may not be present.

      -- Todd

  • Hi! Thank you for the helpful article comparing GIA and AGS. Would you be able to give me your insight/pick of the 3 brilliant round diamonds below? Diamond #1 and #2 are G and VS2. Diamond #3 is H and VS1. Any help would be greatly appreciated. Thank You, Farah
    Total depth between #1-58% #2-56.6% #3-60%
    Table diameter between #1-60.5% #2-61.1% #3-60%
    Crown angle between #1-32.5% #2-33.4% #3-32.5%
    Pavilion angle between #1-41% #2-41.2% #3-41%
    Girdle: #1-med to slightly thick, faceted, 3.5% #2-1.1% to 3.6%, faceted #3-med to slightly thick, faceted, 3.5%
    Culet: #1-none #2-pointed #3-none

    • Hi Farah,

      Thank you for your inquiry. It would be best if I had the diamond grading report numbers, so that I can try to look the diamonds up and see whether any images and additional details might be available. You can send those to me via the Diamond Concierge Service form if you do not want to make that information public.

      The proportions for these round brilliant cut diamonds are outside my preferred range.

      The total depth measurements of #1 and #2 are extremely shallow! And there is usually a lot of light leakage created by having a table facet that is larger than the total depth, especially when the crown angles are shallow like this. It would be really interesting to see reflector scope images for these diamonds! Did you find them online, or at a local jewelry store?

      Things can go either way with a 41.0 degree pavilion angle. If the corresponding pavilion depth is around 43% it is likely to produce a high volume of light return. However, in my experience, things tend to go sideways right around 43.5% which seems to be the critical tipping point where light begins not to strike fully off of the pavilion facets (lower half of the diamond). I suspect that the diamond with the 41.2 degree pavilion angle has a 43.5% pavilion depth?

      -- Todd

  • Thank you for the quick reply, Todd. Sorry, I messed up with my inputs...switched numbers between depth and table. Here are the lab report numbers, GIA 7236191031, AGS 104046879034, GIA 1235046428. Your help is much appreciated.

    • Hi Farah,

      You know, I was actually wondering about that... Instinctually, I thought that the table and total depth measurements might have been reversed, but decided to just go with the information provided.

      The Enchanted Diamonds Cut Score gives GIA #7236191031 a ranking of 88.4% out of a possible 100%. The 2.30 carat, G-color, VS-2 clarity, GIA Excellent cut round diamond has a pavilion angle of 41.0 degrees, which is combined with a pavilion depth of 43.5% which as discussed yesterday happens to be the critical tipping point where light begins not to strike fully off the pavilion facets. It's likely that the 32.5 degree crown angle is going to produce significantly more brilliance (white sparkle) rather than the virtual balance of brilliance and dispersion (colored sparkle / fire) that comes with a crown angle between 34.3 - 35.0 degrees.

      Beware of the "knot" which is listed as being one of the primary inclusions. A knot is an included diamond crystal that breaks through the surface of the diamond. They are similar in concept to a knot that can be in a piece of wood. They can be knocked loose and fall out with time, leaving a cavity in their place. The problem with surface cavities is that they can fill-up with dirt and grime, and look like a dark spot in the diamond. They are very difficult (if not impossible) to keep clean. I generally avoid diamonds with cavities, chips, etch channels, and knots.

      I need the carat weight of AGS 104046879034 to be able to look it up using AGS Report Check.

      The Enchanted Diamonds Cut Score tool gives GIA #1235046428 a rating of 87.8% out of 100%. This is because the 2.06 carat, H-color, VS-1 clarity, GIA Excellent cut round diamond has a 60% table diameter and a 41.0 degree pavilion angle that is combined with a 43.5% pavilion depth. Here again, this is the critical tipping point where light begins not to strike fully off of the pavilion facets. And the crown angle of 32.5 degrees is also pretty shallow. You know from my previous explanation that this is likely to create a lot more brilliance, however it will be at the cost of dispersion / colored sparkle / fire.

      Remember that all of this is really a matter of personal preference and taste. That is why the parameters for the GIA Excellent and AGS Ideal-0 proportions grades are so broad. What appeals to one person may not appeal to the taste of another person. If you're able to see the diamonds in-person, then pick the one that appears to exhibit the highest volume of light return and sparkle factor. However I definitely would not consider buying these diamonds online without the additional insight provided by ASET Scope, Ideal Scope, and Hearts & Arrows scope photographs.

      -- Todd

  • Thank you so much, Todd! I really appreciate how quick and thorough your responses are--wow, it is good to know about knots. I wasn't even aware to look out for them. I will definitely make sure to see the diamonds in person. In terms of the AGS graded diamond, it is 2.018 carats.

    -Farah

    • Hi Farah,

      So the 2.018 carat, G-color, VS-2 clarity, AGS Ideal-0 cut round diamond was graded on the standard proportions based grading platform. Which is why the diamond grading report issued on July 14, 2016 does not provide an ASET Scope image. The Light Performance grading platform has been available for many years now. Which is why it bothers me when diamond dealers choose the lower level grading platform. It makes me wonder what is it that they're trying to hide? I was really hoping that this AGS Ideal-0 cut diamond was going to provide us with the ASET Scope image, because it would have enabled me to demonstrate the effects created by the 41.2 degree pavilion and 43.7 degree pavilion depth combination. Which is not likely to perform as well as a diamond with a pavilion angle between 40.6 - 40.9 degrees.

      Here again, the shallower crown angle of 33.4 degrees is likely to produce a higher volume of brilliance, but it will be at the expense of dispersion (colored light, fire). The benefit of buying this diamond over the GIA graded counterparts is that the measurements stated on the diamond grading report are at least the real averaged measurements. The GIA rounds those measurements off, which makes it a lot more difficult to predict light return.

      -- Todd

  • Hi Todd, Thanks for the advice. Trying to decide between a clean and sparkly GIA 7223246706 or 1.5k GBP more expensive 1166600222 GIA which has a better cut but table inclusion. Any guidance?
    Thx
    K

    • Hello Kim,

      Thank you for your inquiry. I would not recommend buying either one of these diamonds.

      I found a historical listing for the 1.70 carat, F-color, VS-2 clarity, GIA Excellent cut round on Enchanted Diamonds. The diamond is showing heavy obstruction and light leakage under the table facet in the red ideal scope image.

      The pavilion depth is 44% and in my experience the critical tipping point where light begins not to strike off of the pavilion facets is 43.5%. Also, the crown angle of 33 degrees is much too shallow, it's not likely to produce a good balance of brilliance and dispersion, especially with the 80% lower girdle facet length.

      Note that the pavilion depth for the 1.75 carat, E-color, VS-2 clarity, GIA Excellent cut round on Enchanted Diamonds (also a historical listing) also has a 43.5% pavilion depth and is showing signs of light leakage under the table facet in the 12 o'clock region.

      Neither of these diamonds has "super ideal proportions" and those "hearts" are far from that classification, there is too much space around the hearts and too much irregularity in size and shape.

      If you let me know the price range you are working with, along with the range of carat weight, color and clarity, you are willing to consider, I will be happy to help you conduct a search within the scope of my selection criteria.

      -- Todd

  • Hello, just wondering what is your take on buying a diamond at the international diamond center. Is it a reputable diamond dealer?

    • Hello Cristian,

      I've never had any dealings with the International Diamond Center, thus I have no opinion as to their reputation. I find that it is more important to focus on the individual diamonds which each dealer is offering. Because ultimately, you are purchasing the diamond, the vendor is merely the company you are buying it from and those come and go. Thus we should focus on the characteristics of the diamond which you are buying. Feel free to send me diamond grading report numbers for any diamonds which you are considering, I'll look over the details and help you choose the best ones.

      I recommend reading 15 Seconds to Diamond Buying Success and downloading my free diamond buying cheat sheet. Print that out and take it with you when you go shopping! It will enable you to quickly and easily determine whether the diamonds you are being offered are good options or not.

    • Hello Melissa,

      The 1.79 carat, G-color, VS-1 clarity, GIA Excellent cut round from Enchanted Diamonds should be quite stunning! The 40.6 degree pavilion angle should produce a high volume of light return, while the 34.5 degree crown angle produces a virtual balance of brilliance and dispersion. That is white sparkle and colored sparkle, and it should be larger in size and bolder in appearance due to the 75 - 78% lower girdle facet length.

      The reflector scope images indicate that the diamond is gathering light from all the right places and reflecting it back nice and evenly with no major signs of light leakage. I'd say you found a great looking diamond!

      -- Todd

  • Greetings, Todd. Would you please advise on these diamonds: GIA 1253069544; GIA 1258255438; GIA 6262295802; AGS 1040937600007. Trying to find the biggest bang for the buck. THANKS SO MUCH!

    • Hello Andrea,

      Thank you for your inquiry. GIA 1253069544 is a 1.34 carat, E-color, VVS-2 clarity, GIA Excellent cut round diamond from James Allen. The 40.8 degree pavilion angle should produce a high volume of light return, while the 35.0 degree crown angle produces a virtual balance of brilliance (white sparkle) and dispersion (colored sparkle / fire).

      The 80% lower girdle facet length should produce pin-fire type sparkle, which is a little smaller than what would be produced by lower girdle facets in the range of 75 - 78%. Some people refer to this type of sparkle as the disco ball effect, since it is kind of like the sparkle reflected by the tiny mirrors glued on to a disco ball. I was able to find reflector scope images for this diamond on the multiple listing service where this diamond is being offered to the trade:

      Despite the fact that this GIA Excellent cut diamond has ideal proportions, it is clearly leaking light under the table facet, as indicated by the translucent areas visible in both the ASET and Ideal Scope images.

      GIA 1258255438 is a 1.50 carat, F-color, VS-1 clarity, GIA Excellent cut round diamond from James Allen. The 40.6 degree pavilion angle should produce a high volume of light return, while the 34.0 degree crown angle is likely to produce just a hint more brilliance. As opposed to the virtual balance of brilliance and dispersion that tends to come with a crown angle between 34.3 - 35.0 degrees.

      This effect is likely to be heightened by the 80% lower girdle facet length, since our human eyes tend not to be able to fully disperse the smaller sparkle into colored light. At the same time, the lower girdle facets look closer to 78-79% to me in the clarity video; so that effect might be minimized somewhat. I was unable to find any additional images for this diamond.

      GIA 6262295802 is a 1.73 carat, F-color, SI-1 clarity, GIA Excellent cut round diamond from James Allen. The 40.8 degree pavilion angle should produce a high volume of light return. While the 35.5 degree crown angle is likely to produce just a hint more dispersion, as opposed to the virtual balance of brilliance and dispersion that tends to come with a crown angle between 34.3 - 35.0 degrees.

      At the same time, the 80% lower girdle facet length might actually serve to even this out a bit, as it tends to make diamonds look a bit more brilliant (exhibit more white sparkle). The supplier for this diamond provided the following ideal scope image on the multiple listing service where this diamond is offered to the trade. As you can see, it appears to be leaking a substantial amount of light under the table facet based upon all those translucent areas:

      Even if that were not the case, I've got to tell you that I'm not thrilled about the extent of the feathers indicated on the plotting diagram. Think back to your childhood days for a moment, and let's pretend that we're playing paper dolls. Imagine that there is a dotted line running vertical between the upper and lower facet diagrams for this diamond. Then imagine folding the lower plotting diagram (right side) along the dotted line, so that it lines up under the upper plotting diagram:

      Notice how the feathers in the relative 3 o'clock position of the upper plotting diagram, then line up with the feathers indicated in the relative 9 o'clock position of the lower plotting diagram? And then how the feather in the relative 5 o'clock position of the upper plotting diagram, then line up with the feather in the relative 7 o'clock position of the lower plotting diagram? And how the feathers located in the relative 9 o'clock region of the upper plotting diagram, then line up with the feathers indicated in the relative 3 o'clock position of the lower plotting diagram? Um, yea, not really my cup of tea.

      I wasn't able to look up AGS 1040937600007 because I need the carat weight of the diamond in order to do that. Feel free to email that to me via diamonds[insert @ sign]niceice.com or add a comment to this thread and I'll be happy to review it for you.

      I took the liberty of searching James Allen for additional options that meet my selection criteria within the range of characteristics and price that you seem to be considering (based upon that of these other diamonds) and found this 1.31 carat, F-color, VS-2 clarity, James Allen True Hearts diamond. The 40.6 degree pavilion angle should produce a high volume of light return, while the 34.3 degree crown angle produces a virtual balance of brilliance and dispersion.

      The 78% lower girdle facet length combined with the higher degree of optical precision that creates the hearts pattern, should produce sparkle which is larger in size and bolder in appearance. That's what I consider to be more bang for the buck (light performance). Compare the Ideal Scope image provided for this diamond with the Ideal Scope images provided for the diamonds above and you'll see the difference clear as day! The table facet for this diamond is a nice deep red, indicating that it's going to be nice and bright!

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