Best Ideal Proportions for Oval Brilliant Cut Diamonds (Maximum Sparkle)

Hi Todd, I’ve been searching for an oval-shaped diamond for a while, and it seems to be a fairly uncommon shape in stores. Are there any ideal proportions for oval-shaped diamonds that you can recommend? I’m on a budget of about 2500 dollars for the diamond itself, and half-carat to three-quarter carat seems to be the range for my budget, based on what I’m seeing in oval brilliant-cut diamonds with D-E-F color, and good symmetry. Should I also be considering table diameter and total depth measurements? – Stefan

Proportions Chart for Oval Brilliant Cut Diamonds:

While the American Gem Society Laboratory (AGSL) does issue overall cut grades of AGS Ideal-0 for oval brilliant cut diamonds submitted to them for grading if the polish, symmetry, proportions, and light performance grades of the diamond warrant it, the reality is that very few oval brilliant-cut diamonds are submitted to the AGSL for grading because it is extremely challenging to obtain an overall cut grade of AGS Ideal-0 for a fancy shape diamond.

Although there are a limited number of diamond cutters like Brian Gavin who routinely produce fancy shape diamonds that receive overall cut grades of AGS Ideal-0 from the AGSL on the Platinum Light Performance grading platform, such as his Signature Princess cut and Signature Cushion cut diamonds. Unfortunately, Brian Gavin does not produce an oval brilliant cut diamond, and I could not find a single oval brilliant-cut diamond graded by the AGSL with an overall cut grade of AGS Ideal-0, or even one with ideal proportions, within the range of carat weight that you specified.

The AGSL does not publish the proportions criteria for oval brilliant-cut diamonds, thus I can not provide you with the AGSL parameters describing the ideal proportions for oval cut diamonds, however when I was the diamond buyer for Nice Ice, I used to use the proportions chart created by Gemologist David Atlas, formerly of Accredited Gem Appraisers, as the basis for my selection process, but it should be noted that I used this information to narrow down the field of possibilities and then brought the diamonds which were of interest in for physical evaluation and examined them using the various reflector scopes that we rely on to judge the optical symmetry and cut quality of a diamond.

Proportions Chart Oval Cut Diamonds

One of the challenges presented by attempting to select an oval brilliant-cut diamond by the numbers is that diamond grading laboratories such as the GIA, do not provide the crown height or pavilion depth measurements on their diamond grading reports; thus it is important to work with a vendor who is willing and able to bring the diamond in for physical evaluation, and who will provide you with a supplementary computerized proportions analysis using either Sarin, OGI, or Helium technology.

The next challenge is that the vast majority of online retailers do not seem to expend the effort necessary to provide their customers with images of the diamond as seen through an ASET and Ideal Scope, but that’s all right because you can always buy your own ASET and Ideal Scope from David Atlas. The diamond shape selector tool which is available on his web site will also help you to form an idea of what the outline of the oval-shaped diamond you are considering will look like, based upon the length to width ratio.

It is important to evaluate the optical symmetry of the diamond, which is based upon the consistency of facet shape, size, angle, and indexing/alignment, because the proportions of the diamond only take into account the outer shell of the diamond, and are based upon the average of eight individual measurements per section.

Evaluating the optical symmetry of the diamond provides insight into how bright the diamond will appear, where it gathers light from within a room, how light moves through the diamond and is projected outward from the stone, the degree to which it leaks light, and how consistent the facet structure of the diamond is… and none of this is reflected by the symmetry grade which is provided on a diamond grading report, so it’s not enough to simply limit your search to diamonds which have a polish and symmetry grades of Very Good, Excellent or Ideal.

The Bowtie Effect in Oval Shaped Diamonds:

Plotting diagram for oval cut diamonds explaining the cause of bowtie effectYou will also want to take the static contrast or levels of contrast brilliance into account, as well as the bowtie effect (or bow tie effect if you prefer) which is created by the difference in the length and shape of the lower girdle facets, as indicated in the graphic provided to the left. The intensity of the bowtie effect in an oval-shaped diamond is affected by not only the facet structure and design but also the angle and length of the lower girdle facets. This particular facet design is for a modified oval brilliant cut diamond.

Which brings up the subject of the wide range of facet designs used to cut oval-shaped diamonds, since these diamonds are produced from diamond rough which is irregular in shape, and which is not symmetrical like the diamond rough used to produce round brilliant cut diamonds, practically every oval brilliant-cut diamond exhibits a slightly different facet structure.

As a result of the wide range of facet designs incorporated in the production of oval cut diamonds, there can be a vast disparity in both the volume of light return and the type of sparkle produced by each oval-shaped diamond. However, it is reasonable to assume that tighter proportions will yield a higher volume of light return and better optical symmetry will result in more sparkle. This tutorial on how to use the Ideal Scope and ASET Scope for fancy shape diamonds provides some great examples of fancy shape diamonds that exhibit various levels of optical symmetry and light leakage.

Shopping for Oval Shaped Diamonds by Proportions:

Since I’m not aware of a single online diamond dealer who specializes in oval brilliant ideal cut diamonds, I  proceeded to search for oval cut diamonds on Blue Nile, search for oval cut diamonds on James Allen, and search for oval cut diamonds on Ritani, using the parameters for total depth (59 – 63%) and table diameter (53 – 61.5%) as suggested in the legacy proportions chart for oval-shaped diamonds created by David Atlas back in 1998. Since I want to increase the odds of finding oval-shaped diamonds that will exhibit a higher level of cut quality, I further limited the search to options graded by the GIA or AGSL with Excellent or Ideal polish and symmetry.

Since I found practically nothing available under the parameters for total depth and table diameter as defined in the column titled ideal cut, I expanded the parameters to the range suggested for the premium cut category, then I flipped through the diamond grading reports to check out the inclusions and eliminated any options which did contain inclusions which don’t meet my selection criteria and eliminated diamonds with a girdle edge which was thicker than I prefer. Here is what was left in order of carat weight:

0.50 carat, D-color, VS-2 clarity, oval shaped diamond from James Allen

0.50 carat, E-color, VVS-1 clarity, oval shaped diamond from James Allen

0.50 carat, E-color, Internally Flawless, oval shaped diamond from Blue Nile

0.51 carat, D-color, VS-1 clarity, oval shaped diamond from Blue Nile

0.51 carat, E-color, VS-1 clarity, oval shaped diamond from Ritani

0.52 carat, D-color, VS-1 clarity, oval shaped diamond from Blue Nile

0.52 carat, F-color, VS-1 clarity, oval shaped diamond from Blue Nile

0.53 carat, D-color, VVS-1 clarity, oval shaped diamond from Blue Nile

0.54 carat, D-color, VVS-1 clarity, oval shaped diamond from Blue Nile

0.55 carat, D-color, VVS-2 clarity, oval shaped diamond from Blue Nile

0.55 carat, E-color, VS-1 clarity, oval shaped diamond from Blue Nile

0.56 carat, D-color, VVS-1 clarity, oval shaped diamond from Blue Nile

0.64 carat, D-color, VVS-1 clarity, oval shaped diamond from Blue Nile

As you can see there are a wealth of oval brilliant cut diamonds available online which have the potential to be exceptional looking diamonds based upon the Legacy AGA chart showing describing the ideal proportions for oval cut diamonds, but the diamond details pages provided for the diamonds referenced above do not contain images of the diamonds as seen through an ASET Scope or an Ideal Scope.

A client and I tried to obtain ASET and Ideal Scope images from Ritani for an emerald cut diamond lately and were told that they do not provide them for fancy shape diamonds, however, they did conduct a Virtual Gemologist appointment with the client online to assist her with narrowing down the options, and then sent the diamond to a local jewelry store for her to see in-person (sales tax applies)

James Allen certainly has the capability of providing ASET and Ideal Scope images for fancy shape diamonds, although I’ve never asked them to do so, and don’t know what their response will be… but they tend to be pretty accommodating if I ask real nice!

The least likely to be able to provide us with diamond clarity photographs and reflector scope images is Blue Nile because they are either unable or unwilling to do so… I haven’t decided which yet, but suffice to say that you can always order any of the diamonds listed above and simply return it for a full refund if you don’t like it for any reason since all of the vendors offer exceptional inspection and return policies.

Todd Gray

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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