August 25

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GIA Excellent vs AGS Ideal cut diamonds, which lab provides the best insight into diamond cut quality?

By Todd Gray

August 25, 2014


GIA Excellent vs AGS Ideal:

“Can you tell me about the differences between GIA Excellent vs AGS Ideal Cut diamonds. I am in search of a magnificent diamond!! Budget: $3,650 Carat Weight: .7-.75 Cut: Ideal (AGS) or Excellent (GIA) Color: F Clarity: VS1 Table: 53-58 Depth: 59-61.8 Crown Angle: 34-34.9 Pavilion Angle: 40.6-40.9 Symmetry: Ideal or Excellent Polish: Ideal or Excellent Girdle: thin-slightly thick L/W Ratio: 1-1.01 Cutlet: pointed or none.

I have found a few diamonds within these parameters on Blue Nile. I would like to know if you trust the quality of the diamonds on these sights, or if you believe I can find a better diamond elsewhere. Some sights, including a few that come recommended by you, are more expensive than the ones I have mentioned.”

Is there a reason for this or is that just the nature of the market? Are the diamonds on some websites just higher quality? I’m having trouble reading into this because everything I am able to come up with is also GIA or AGS certified. I welcome any and all comments, advice, feedback, etc. and also a diamond recommendation if you are able to come up with one! Thank you for all your help!”

All Ideal Cut Diamonds are NOT created equal:

Round brilliant ideal cut diamonds are produced in different levels of diamond cut quality, which is the term used to refer to the consistency of facet shape, size, alignment, and indexing (spacing) from one facet to another ~ this is a level of symmetry that is graded beyond the meet point symmetry grade that appears on diamond grading reports; it is judged using reflector scopes, such as the Ideal Scope, ASET scope, and Hearts & Arrows scopes, inclusively, meaning that each scope has a designated purpose and all three are needed to get a complete picture of the optical symmetry of the diamond.

There is also the matter of whether the offset for the crown and pavilion angle is matched up properly with the right crown height and pavilion depth percentages because those angles only represent the angle that those edges are cut to as it comes off of the girdle edge of the stone and travels towards the opposing endpoint; but a primary factor of light performance is the actual depth of those two sections; and a lot of diamond cutters don’t partition the diamonds properly, in an effort to retain carat weight, while still hitting the magic numbers that people look for… the reality is that the diamond industry knows full well that very few diamond buyers actually understand how diamonds should be partitioned for maximum light performance.

GIA Excellent vs AGS Ideal cut diamonds:

In my experience, the majority of diamond cutters who produce round brilliant ideal cut diamonds that exhibit a higher degree of optical symmetry and overall diamond cut quality, submit their production to the American Gem Society Laboratory (AGSL) for grading.

I’ve always assumed that the majority of diamond cutters who produce round brilliant ideal cut diamonds of the highest diamond cut quality / optical symmetry, use the AGSL because they prefer the insight provided by the ASET; but it might also be simply because an overall cut grade of AGS Ideal-0 is considered to be the pinnacle of grading for diamonds of this cut quality. In other words, it is more difficult to achieve than GIA Excellent. At the same time, it costs more to achieve in terms of the expense involved in cutting the stone. Although this may be true, I thought I’d ask a few diamond cutters to find out why they send the majority of their production to the AGS instead of the GIA for grading.

Brian Gavin on GIA Excellent vs AGS Ideal Cut:

My conversation with fifth-generation diamond cutter Brian Gavin about why he sends all of the Brian Gavin Signature Diamonds to the American Gem Society Laboratory for grading, left me with the impression that he simply prefers the insight provided by the Angular Spectrum Evaluation Technology (ASET) and the Light Performance-based grading platform.

Brian Gavin indicated that in his experience, the GIA and AGSL grade similarly for polish and symmetry, thus the only real difference between the two gemological laboratories is that the AGSL takes the light performance of the diamond into account, where the GIA does not.

I presented the same question to Paul Slegers of Crafted by Infinity via email and this is what he wrote back:

“Bigger houses try to sell diamonds in these sizes as whole-businesses; meaning they come as a single large parcel with numerous graded diamonds in the 50s 60s 70s 80s and 90s included. So they are not selling 70s separately – they are package-priced.

If these houses were to target some of those diamonds for AGSL reports the greater planning and tooling needed could imply 2-3x as much time in production as cutting to the simpler 2D requirements of GIA. This would not only slow the production of one segment of the business (70’s in your example) it would slow the sale of the much larger parcel.

Doing this all year would cause turnover to slow by 50-75%. Our production and our mission are different. First, we produce each stone with identical purpose so we’re already committed to being pedantic in the timeline. Second, we sell we each diamond individually, whether 0.20ct or 20ct. Third, our diamonds all exceed AGS-0 as a by-product of our mission and vision, so there is no reason to hesitate to send them anywhere. And lastly, our target market appreciates the value of the technically superior AGSL report – and although we (personally) feel it is somewhat wide compared to what we do, we support AGSL as currently the most suitable document in which to wrap our product.”

Crafted by Infinity Diamonds:

Crafted by Infinity diamonds are distributed via my friend Wink Jones who operates High Performance Diamonds. At the moment, they don’t have anything suitable that I can tempt you within your desired range of characteristics. However, the reason why this 0.712 carat, F-color, VS-1 clarity, Brian Gavin Signature round diamond, and comparable Crafted by Infinity diamonds costs more than some of the other options which you’ve found, is because of the combination of proportions, which includes the crown height and pavilion depth measurements, which are in-line with the crown angle and pavilion angle measurements, but also the degree of optical symmetry that is evident in the reflector scope images.

Another factor that people rarely take into account are the length of the lower girdle facets, which have a direct effect on the width of the pavilion main facets (arrows pattern) and this will affect the type of sparkle emitted by the diamond. The 76% lower girdle facet length of this Brian Gavin diamond is likely to produce sparkle which is larger, bolder and brighter, than the sparkle exhibited by this 0.71 carat, F-color, VS-1 clarity, round diamond. Which has 80% lower girdle facets and thus should exhibit sparkle which is more like pin-fire. Of course, the trick is knowing which type of sparkle you personally prefer.

In terms of the volume of light return and the balance of brilliance (white sparkle) and dispersion/fire (colored sparkle), the two diamonds should be relatively equal. However the higher degree of optical symmetry exhibited by the Brian Gavin Signature round diamond should result in a higher number of virtual facets, which in turn should create a little more sparkle, and it is the degree of cut precision which is driving the price higher, so everything is relative.

In terms of production standards, the diamond from Enchanted Diamonds is easily within the Top 1% of the annual production for round brilliant cut diamonds, while the diamond from Brian Gavin is within the Top 0.001% because of the higher degree of optical symmetry. It’s kind of like the difference between a stock Porsche 911 and one equipped with a turbocharger, the reality is that I’d be happy with either one, but I’m going to get a bit more performance from the one equipped with the turbocharger… now whether I’m willing to pay for it is another matter entirely, since we all have a budget to work within, but this is the answer to your question pertaining to why diamonds which seem similar on paper, can reflect dramatically different price points.

Blue Nile diamond reviews:

Of the options currently available from Blue Nile, the one which is of most interest to me is this 0.70 carat, F-color, VS-1 clarity, round diamond from Blue Nile which has a 40.8 degree pavilion angle (43% depth) that is offset by a 34.5 degree crown angle (14.5%) with a medium to slightly thick, faceted girdle and no culet. The 80% LGF’s are likely to produce sparkle which is more like pin-fire, this is kind of like the sparkle reflected off of a disco ball.

Would you do me a favor if you decide to purchase this diamond from Blue Nile and do so by clicking on the link provided, and not calling to reserve the diamond because they only track affiliate referrals that result from click through traffic… that is if you don’t mind my being credited for the referral, and if you can then follow up by sending me the order confirmation number provided by Blue Nile, so that I can ask my rep at Blue Nile to track the order, I’d appreciate it – they are the worst company to work with as an affiliate 🙁

The only other option that I’m seeing with BN is this 0.70 carat, F-color, VS-1 clarity, round diamond from Blue Nile, but the proportions are kind of on the edge of my preferred scale, so honestly, I’d grab the other one… the combo of the 34.0 degree crown angle / 40.6 degree pavilion angle is shallow/shallow and that isn’t all that great.

Brian Gavin Coupon Codes:

These are the best options that I’m seeing at the moment. Let me know if you found any others that you want me to look over, and/or if you have additional thoughts and questions. I almost forgot to mention that you should contact me if you decide to go with either the diamond from Brian Gavin because I can provide you with a coupon code that will save you some money on a setting ordered in conjunction with a diamond.

About the author

A mad scientist with a passion for improving diamond cut quality to maximize light performance and sparkle factor. I speak geek in degrees of optical precision between bouts of freediving. My ghostwritten ramblings haunt the rabbit holes of information found on many diamond vendor sites. Diamond buyer, author, consultant, errant seeker of deep blue water.

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