“Can you explain how to judge diamond visual performance online? I’m having a hard time deciding between a few since I can’t actually view the stones for performance. Thanks in advance and for all the useful advice you provide.” — Dave.
Well, I’ve got good news for you, Dave because I can definitely teach you how to judge diamond visual performance online. As a matter of fact, you can tell a lot about a diamond based on the information provided by the two vendors that you reference in your email:
With that in mind, let’s take a look at the factors that dictate light performance.
The visual performance of a diamond is controlled by the diamond cut quality which is a combination of proportions, polish, symmetry. In addition, a little known factor called Azimuth Shift plays a major role in light performance. As a matter of fact, it’s pretty simple to judge diamond visual performance based on the first three factors:
By looking at the grade assigned for these factors under the Cut Quality section of the diamond grading reports issued by gemological laboratories such as the AGS or the GIA. However, none of the major laboratories actually take Optical Precision into account when determining the cut grade of a diamond. I find that kind of strange since it dictates the Sparkle Factor of a diamond.
So the first thing that I look at when considering round brilliant ideal cut diamonds is the information provided on the lab reports, I take a look at the polish, symmetry and proportions grades as indicated on the lab reports to ensure that the grade for each factor is either AGS Ideal or GIA Excellent which should result in an overall cut grade of either AGS Ideal 0 or GIA Excellent which are the top grades available from the AGS and GIA gemological laboratories for these factors. Then I actually look at the measurements indicated on the proportions diagram for the diamond on the lab report to ensure that the measurements fall within the following range which is my personal preference for maximum light return:
Total depth between 59 – 61.8%
Table diameter between 53 – 57.5%
Crown angle between 34.3 – 34.9 degrees
Pavilion angle between 40.6 – 40.9 degrees
Girdle between thin to slightly thick, faceted or polished
Culet either AGS pointed or GIA none
Now it is important to note that there are other combinations of crown and pavilion angle which will offer a similar degree of light return in terms of volume, however the range specified above eliminates a lot of the guesswork and will help you to quickly narrow down options when there are lots of diamonds to choose from… if you happen to be considering diamonds weighing more than 2.5 carats, it is highly unlikely that you will find very many options available within the range specified above at the current time and the specific offset for crown and pavilion angle will need to be carefully considered for each diamond (and I’m happy to do so if you just ask).
In a moment we’re going to look at the four diamonds which David specifically referenced in his email and we’re going to walk through the selection or rather the elimination process by first looking at the proportions, polish and symmetry grades of the diamond as outlined above, then we’re going to get into the nitty gritty hidden factors of selecting diamonds for visual performance by very carefully looking at the images of the hearts and arrows pattern as well as the images provided for how the diamond looks when viewed through and ASET Scope and an Ideal Scope… but first I want to remind you that the mere fact that all four of these diamonds have proportions which are well within the range specified for the zero ideal cut proportions rating by the AGS Laboratory combined with either AGS Ideal or GIA Excellent polish and symmetry that they are essentially in the Top 1% of annual production for round brilliant cut diamonds… so they’re all great diamonds in terms of visual performance, but we’re looking for “the one” which is the Cat’s Meow in terms of diamond cut precision and visual performance… with that said, here goes:
The first diamond to consider is a 1.62 carat, round brilliant ideal cut diamond from James Allen which is graded by the GIA Laboratory as being VS-2 in clarity and H in color with negligible fluorescence and it gets automatically rejected from the pile simply because it has a total depth of 62% which is beyond the range of 59 – 61.8% previously stated… but since this is a tutorial let’s talk about why.
Diamond prices are calculated on a combination of Carat Weight, Clarity, Color and Cut which is actually Diamond Cut Quality and NOT shape… quite simply the total depth of the diamond which is indicated by the GIA Laboratory as being 62.3% is a result of the crown angle of the diamond being a little too steep at 35.0 degrees which is offset by a pavilion angle of 41.0 degrees which is just a little too steep and a medium to slightly thick girdle, so it’s like all three of the primary sections of the diamond are just a tad too thick and thus this diamond would honestly never cross my radar during my selection process because I would have set the Advanced Options which are available within the diamond search engine on the James Allen web site to reflect my preferred range which is specified above.
But “why is this a problem in terms of visual performance” is the question at hand and it’s quite simply a matter of how the two primary reflective surfaces or “mirrors” of the diamond are aligned, they’re both set a angles which are slightly steep and thus a little less light is going to be directed out the top of this diamond than would be if both the crown and pavilion angle were cut just a little shallower… and once again, keep in mind that this diamond is within the Top 1% of the annual production for round brilliant cut diamonds, so it’s probably gorgeous, but it’s not cut within the tolerance of the criteria of my personal selection criteria and thus it would be rejected by me. I didn’t get the reputation of being a Diamond Snob without cause.
The diamond might seem to looks pretty good as seen through an Ideal Scope (pictured above left) however all that grey color under the table facet is actually an indicating of light leakage, and the Hearts image (right) indicates a variance in the size and shape of the hearts, combined with a little bit of twisting in the tips of the hearts and a variance in the size and shape of the small arrowheads located beneath the tips of the hearts and some bleeding over between the tips of the hearts and the formation of those arrowheads which is usually an indicator of Azimuth shift which is a slight variance in the alignment of the facets in terms of the upper and lower positions of each section of facets if you were to think of them in terms of their relative position on the face of a clock… this is quite common and has less to do with the amount of light being returned than the size of the flashes of sparkle and whether that sparkle will be in the form of more brilliance or dispersion because of how our human eyes are able to discern color based upon the size of the flashes of light.
The easiest way for you to consider this when trying to judge diamonds online for visual performance is that the sparkle factor of the diamond is likely to be higher when there is less Azimuth shift in the diamond because the more precise alignment of the facets will result in a higher number of virtual facets which result in more sparkle… Virtual facets are the facet shapes which are created by the overlapping of actual facets over another, it’s like one big whopping kaleidoscope of facets being created virtually within the prism of the diamond as either you or the diamond is moving… and the more precise the hearts and arrows pattern of the diamond happens to be, the more likely the chance of a higher number of virtual facets being produced.
Finally if I hadn’t actually rejected this diamond initially based upon the proportions and subsequently because of the variance in the size and shape of the hearts, twisting of the heart tips and variance of the arrowheads, I’d take a look at the inclusions indicated on the plotting diagram of the lab report for this diamond which are indicated as being cloud, crystal, feather, needle and determine that those are all acceptable… Note that I automatically reject for knots, cavities and twinning wisps because they have the “potential” to present a “potential durability risk” and since I’m a diamond snob, I don’t see the need to consider such things.
All right, Option #2 is a 1.66 carat, I color, VS-2 clarity round brilliant ideal cut diamond from James Allen which happens to have a total depth of 62.1% so you know what just happened right? That’s right, it got rejected because the total depth falls just outside of my preferred range of proportions specified previously… but actually this diamond is a little more interesting to me because it is graded by the AGS Laboratory on their Platinum Light Performance grading platform and thus it has actually been evaluated for Light Performance which is something not currently offered by the GIA Laboratory and I happen to put some weight in it as a developing method to be considered during the diamond selection process. Looking at the actual proportions diagram provided on the lab report for the diamond, the crown angle of the diamond is indicated as being 35.0 degrees which is just barely beyond the preferred range of proportions specified above, but more importantly the pavilion angle of the diamond is 40.9 degrees which is excellent in terms of the reflective mirror which is created by the pavilion. Next I take a look at the plotting diagram of the diamond on the lab report and determine that the primary inclusions consist of diamond crystals, which are simply tiny diamond crystals that were absorbed by the larger diamond crystal as it formed. Thus far the only thing causing this diamond to be “rejected” is a little bit of total depth and a crown angle which is just a little beyond my center range preferences, so let’s take a look at the scope images:
Things look pretty good in terms of the Ideal Scope image (pictured left) and there is a decent amount of consistency in terms of the size and shape of the hearts (pictured right) with a minor degree of twisting in the tips of the hearts, so I’m inclined to keep this diamond around as a “safe option” just in case we don’t find anything better.
Option #3 is a 1.68 carat, I color, VS-2 clarity, round brilliant ideal cut diamond from James Allen which is graded by the AGS Laboratory on the Platinum Light Performance grading platform. Here again, the total depth of the diamond at 62.2% is grounds for automatic rejection based on the criteria I established at the beginning of this article in terms of proportions. However the crown angle of the diamond is stated as being 34.9 degrees and it is offset by a pavilion angle of 40.8 degrees so I’m willing to look past the total depth of the diamond and give it a little more time in the arena of consideration because the “mirrors” of the diamond are within my preferred range and a little total depth will really only cost a little bit of visible surface area in terms of outside diameter. Once again the primary inclusions are listed on the lab report as being crystals, so we move forward to evaluating the diamond as seen through an Ideal Scope and a Hearts and Arrows viewer.
The diamond looks good through the Ideal Scope (pictured above left) and there is more consistency in the size and shape of the hearts with only a little bit of twisting being visible in a few of the tips and very little variance in the size and shape of the arrowheads… this is probably my favorite of the options presented from James Allen thus far, it would definitely be between this and the 1.66 carat reviewed just above it.
Option #4 is a 1.70 carat, I color, VS-1 clarity, round brilliant ideal cut diamond from the Brian Gavin Blue Collection which this diamond was selected for because it exhibits strong blue fluorescence. The diamond was graded by the AGS Laboratory on their Platinum Light Performance grading platform and has a total depth of 61.0% with a table diameter of 58.6% with a crown angle of 34.8 degrees offset by a pavilion angle of 40.6 degrees. This diamond would not have crossed my radar during my selection process because of the 58.6% table diameter, but looking past that to the crown and pavilion angle offset which is more important, it should be a lively looking diamond because the “mirrors” of the diamond are properly aligned for maximum light return. The table facet which is the very top flat facet of the diamond will face up a little larger than my personal preference, but the words “personal preference” are the key factor of this sentence… everybody tends to like their diamonds cut a certain way and my preference leans towards the original “sweet spot” which comprise the very center region for the original parameters of the AGS proportions guidelines. Now Brian Gavin does not provide images of the hearts patterns for diamonds selected for the Brian Gavin Blue collection because the focus of the diamonds selected for this offering is the existence of blue fluorescence but Brian tells me that the diamonds are produced by the same diamond cutters who produce the Hearts and Arrows Diamonds for the Brian Gavin Signature Collection, so it’s reasonable to assume that the visual performance will rival the diamonds from that offering… at least that has been my experience when I’ve viewed the diamonds thus far. So I’m inclined to keep this one in the running and thus we have three options worthy of consideration, but not one which falls 100% within my preferred range of proportions.
Needless to say that upon completing my evaluation of the four diamonds referenced in David’s email and not finding a single one which is a 100% hit in terms of meeting all of the factors of my selection criteria, I went on a little search of my own to try and find viable options within the range of 1.55 – 1.99 carats, H to I color, VS-2 to VS-1 in clarity and I didn’t find anything that was comparable to these options in terms of price… so if I were to personally make the selection based upon the options currently presented, I would do it in reverse order with first choice being the 1.70 carat, Brian Gavin Blue for the simple reason that the additional details provided by the computerized proportions analysis indicate that the spread between the high and low measurements for the crown and pavilion angle is extremely minimal which provides additional insight into the precision of the diamond cut quality. The measurements for crown and pavilion angle which are stated on the lab reports are the average measurements of eight measurements which are taken for each section, in this particular instance the average crown angle of 34.8 degrees is based on a low of 34.8 and a high of 34.9 degrees and the average pavilion angle of 40.6 degrees is based on a low of 40.5 and a high of 40.7 degrees which is extremely tight and is an indication that the diamond cut precision is exceptional. The opposite could be true of any stone with the same average measurements indicated on the lab report, for instance the average crown angle of 34.8 degrees could be the result of a spread as broad as 33.8 – 35.8 degrees and the average pavilion angle of 40.6 degrees could be the result of a low of 39.6 degrees and a high of 41.6 degrees which would make for a pretty wonky stone and unfortunately I’ve seen “ideal cut diamonds” cut with a lot of variance between the high and low measurements which is why I always like to see the results of a computerized proportions analysis when evaluating diamonds for visual performance… in absence of that kind of detailed information, we’re left with only the limited information provided on the lab report and what we can discern from the scope images.
So in summary, the order of my preference would be from the bottom up, I’d be inclined to purchase the 1.70 carat from Brian Gavin, then the 1.68 carat from James Allen and then the 1.66 carat from James Allen and I’d pass on the 1.62 carat entirely since better options are readily available. Hope that helps.
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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