AGS Ideal Ovals by GIA

Shopping for an oval diamond today leads many down a path that ends before the key attribute of cut quality is fully resolved, leaving significant uncertainty (and axiety) in the purchase process.That is why an overall cut grade on a laboratory report is essential, and why GIA has begun addressing this shortcoming with the AGS light performance technology they acquired in 2022.

With the surge of interest in oval shape diamonds in the last few years, and the challenges consumers have in evaluating them from a cut quality perspective, it is a good time to review the light performance system AGS Laboratories developed, and which has been deployed by GIA in limited fashion in the years since their acquisition of this sophisticated technology. First, it should be noted that currently the only GIA reports featuring AGS Ideal grades are those for diamonds which qualify as Ideal, including both rounds and fancy shapes. And the AGS Ideal grade is issued by GIA as an addendum to the standard GIA report. It is not found directly on the standard report at this time, though there is a notation at the bottom of the report indicating it is available along with a QR code that takes you to the digital file. GIA has suggested that a more robust implementation of AGS cut grading will be rolling out in 2027, but it is still uncertain exactly what that will look like. Currently, shoppers looking for diamonds with this dual certification will find them in GIA reports featuring the AGS Ideal addendum.

Before we look specifically at the cut grading of oval diamonds, it is instructive to review the basics of AGS light performance grading. This system is the most scientifically sophisticated, peer reviewed cut grading system in use today by any major laboratory. It is based on ray tracing an accurate 3D model of the diamond and mathematically calculating brightness, leakage, contrast and fire. Fancy shape diamonds can have different optical aspects that require specific scrutiny (such as bowtie in ovals), and adjustments are made in the grading metrics for different quality factors specific to each shape.

As GIA puts it in their 2024 study on fancy cut grading,

Note: Some online merchants put cut grades on fancy shapes that are presumably derived from the limited parameters found on laboratory reports. These claims should be taken with a grain of salt. In particular, any fancy shape that is labeled as Ideal, if it is not accompanied by an AGS Ideal report from GIA or offered with advanced light performance images to support the claim, should be considered “marketing”.

• Why Parametric Grading for Fancy Shapes Doesn’t Work
• Length to Width Ratio
• Bowtie Effect
• The Role of Crushed Ice in Fancy Cut Quality
• Why are AGS ideal Ovals so Rare
• Why the GIA AGS Collaboration is a Game Changer
• Conclusions

Many attempts have been made to create simple cut grading tables for fancy shapes based on the few averaged and rounded parameters found on standard laboratory reports. But none has been widely embraced in the market because they are inherently unreliable in their simplicity.

In typical ovals with four pavilion mains and eight bezel facets there are 18 parameters, three times more than round brilliants!

A marquise has 19 parameters, and a pear shape can potentially result in as many as 57 parameters.

According to GIA, “The much greater number of parameters for fancy shapes precludes any kind of grade prediction base on averaged and rounded proportion combinations. Any predictive cut grading for fancy shapes must be based on a 3D representation for the diamond, such as the wireframe files produced by non-contact measuring devices.”

While other researchers studying light performance in polished diamonds, such as Octonus and the Lexus Group, have made very important contributions to the field, the research team at AGS Laboratories developed the only widely used system for grading cut quality that is scientifically vetted, repeatable, and well regarded in the marketplace. As GIA begins actively deploying this technology, that reach promises to grow exponentially over the next few years.

Many consumers tend to focus on length-to-width (L/W) ratio in evaluating ovals. And while L/W ratio helps to describe a general sense of elongation in ovals, it does not paint a true picture of the shape. Variations in shoulder, head and belly areas can significantly alter the visual outline as well as impacting light performance. That said, GIA reports that oval ratios around 1.4 are the most commonly submitted to the lab.

The optical feature that gets the most attention in ovals (also pears and marquises) is something called the bowtie effect, or just “bowtie”. It is seen in most ovals across the middle of diamond as a horizontal hourglass pattern. At close range it can look dark, resembling a black bowtie. Depending on lighting and camera setup, the bowtie does not always look dark. The darkness generally comes from obscuration of the light either from head shadow when viewing in person or reflection of the camera lens in photography (which serves as a proxy for head shadow). The light obscured from the highest angles overhead causes the large virtual facets reflected by the pavilion facets to appear non-illuminated. This property is important as it contributes contrast to the light performance of the diamond, so long as it is in the right amount and distribution the contrast is positive and adds to scintillation and the perception of brilliance. However, in excess contrast can make the diamond look dark under normal close examination.

Even if a bowtie does not appear dark, it can have a negative impact on the optics of the diamond. Large virtual facets that are contiguous with areas of very small virtual facets (so-called crushed ice), can give the stone a disjointed look and detract from a consistent visual flow. Very small virtual facets in the ends of an oval can get blurry, exacerbating this problem. A well cut oval diamond has a balance in virtual facet make-up in terms of size and distribution, with overall crispness.

Prominence and persistence are important factors in evaluating bowtie. As mentioned above, the bowtie effect, while a feature of most ovals and other elongated stones, is not necessarily a positive feature. Therefore, it should not be prominent in the appearance of the diamond. While it is visible at some tilt angles, it should not be persistent through a large range of normal viewing angles. This is one of the factors that the AGS light performance grading system takes into account in assessing ovals and other shapes that feature the bowtie effect.

A term commonly used in the trade for diamond cuts producing myriad tiny virtual facets is “crushed ice”. Virtual facets are the reflections produced by a polished diamond that are far more numerous than the physical facets on the stone. This is because a single physical facet can reflect light rays from multiple directions at once. Some diamond cuts appear as primarily crushed ice where others have crushed ice areas within them. Crushed ice, due to very small virtual facets, produces a twinkling flavor of light performance, as opposed to broad flash. In elongated shapes such as oval, crushed ice tends to appear in the ends.

The quality of crushed ice in a diamond is variable. It can show different mounts of contrast from distinct and bright (crisp) to muddled and gray (sometimes referred to as “mush”). The tiny virtual facets of crushed ice are also more sensitive to any transparency deficits in the diamond crystal which can diminish a diamond’s sparkle.

Ovals and other fancy shapes that have partial crushed ice are subject to appearing disjointed when areas of very small virtual facets are contiguous with areas of large virtual facets such as those in the midsection or bowtie area. This can make the bowtie effect more prominent and disrupt the visual flow of the diamond’s optics.

An AGS Ideal report is arguably the strictest pedigree that any polished diamond can have in terms of cut quality. The light performance grading system employs ray tracing to mathematically measure the quantity and quality of the light output of the diamond in terms of brightness, fire, contrast and leakage.In the caseof fancy shapes like oval, it also analyzes critical aspects such as the prominence and persistence of the bowtie effect.

The vast majority of ovals in the marketplace have not been analyzed for cut quality to this degree, leaving consumers unsure about the most important aspect of diamond beauty.

This is a very interesting question, and one whose answer has a number of different facets, so to speak. First, even though GIA has been offering AGS Ideal reports since soon after acquiring the AGS light performance grading technology in 2022, they have only passively promoted it. It is an addendum report to the standard grading report which needs to be requested at the time the diamond is submitted to GIA. Since there is no overall cut grade on a standard GIA report for a fancy shape diamond, manufacturers have had no incentive to cut to any standard greater than achieving Excellent in polish and symmetry, which are “finish” grades that are not the main drivers of light performance. And, most importantly, the difficulty in achieving AGS Ideal is a significant challenge for most cutters. Only when there is a clear incentive for them to do so will cutters with the skills and technical know-how, and a willingness to spend more time and material (lower yield from rough), start developing the ability to hit this elite standard.

Whiteflash has been working with our cutters for over a year and is now able to stock an initial inventory of AGS Ideal ovals. You can review these very special diamonds in our Expert Selection category where they are posted with full diagnostics including ASET, Ideal Scope, HD Video and of course the GIA report with AGS Ideal addendum.

It is likely that when GIA rolls out a cut grade for fancy shapes on standard reports that it will be in line with their current cut grade system for rounds. That is, the familiar Excellent, Very Good, Good, Fair, and Poor structure. AGS Ideal reports may continue to be reserved for the very best and require that the stone meets the GIA Ex grade for polish and symmetry, as well as having Ideal light performance under the AGS system. At that point, there will be incentive for cutters to at least achieve the Excellent overall cut grade, which will significantly increase the number of well-cut ovals and other fancies, as it did for general cut quality in rounds when GIA finally released that system in 2005.

AGS and GIA are sister organizations that go all the way back to their founding in 1934. In that time they have had a mutually supportive and collaborative relationship, both pursuing a mission to bring knowledge and integrity to the diamond and gem industry. So it is not surprising that with the modern interest in diamond cut quality that they would be closely aligned on the topic. But the new arrangement with GIA having acquired AGS light performance technology is of monumental importance to the trade as it combines the world-class AGS ray tracing system with GIA’s unmatched ability to conduct carefully controlled, large scale observational studies. The synergy of this pairing cannot be overstated in the pursuit of a cut grading system for fancy shape diamonds that is scientifically rigorous, consistent, repeatable, and fully validated by real world testing.

“Despite the daunting task of evaluating billions of possible fancy-shape combinations that manufacturers can produce, ultimately human observations provide the essential ground truth for tuning any predictive system.” GIA Gems and Gemology Fall 2024

A very important aspect of this “division of labor” is recognizing that the AGS light performance analysis is based on a model of the diamond and the mathematical behavior of light, and gets no information about the diamond’s crystal transparency or inclusions. The 4Cs grading on the GIA report is therefore critical to a full understanding of a diamond’s actual performance from the perspective of a human observer.

Furthermore, the GIA draws a line in their training materials between the cut grade that appears on the GIA report, and the AGS Light Performance grade on the supplemental. The relationship between the GIA Excellent grade and the AGS Ideal grade is explained thusly, “The method used by GIA to determine a diamond’s cut grade is notably different from the method used to determine whether a diamond qualifies as an AGS Ideal®. Only a very small percentage of all faceted diamonds will have both the optimal optical symmetry and high light performance needed to qualify for an AGS Ideal®”

The combined comprehensive analysis, featuring the light performance component, serves to subdivide the GIA Excellent cut grade by identifying the truly elite performers in the Triple Ex grade. It remains to be seen exactly how the overall cut grade on standard GIA reports on fancy shapes will be structured, but considering the wide variations seen in the observational studies, the Excellent grade will likely be very broad to allow for taste factors. This will make the AGS light performance element extremely important for consumers looking for the elite performers within the GIA Ex grade.

A new day is arriving in laboratory diamond grading that will have significant impacts on the diamond industry as a whole. An accurate and reliable cut grading system for fancy shape diamonds has long eluded the industry and made it more difficult for consumers to shop for these desirable shapes and faceting styles. The combination of GIA 4Cs grading with AGS light performance grading is in the process of changing that in a big way.

Oval shape diamonds are one of the most popular of the fancy shapes on today’s market, and they have perplexed shoppers who currently have no good way to independently judge cut quality, which is widely considered to be THE most important aspect of diamond beauty. Whiteflash has been working with our cutters for over a year to bring AGS Ideal ovals to our in-house inventory. You can find these exceptional stones in our Expert Selection category.

The complexity of the geometry of an oval shape defies any accurate grading system based upon a few basic parameters. How the diamond actually handles light cannot be understood without using a light ray tracing technology such as that developed by AGS.

With the acquisition of that technology GIA now provides a combination of the best 4Cs grading with the best light performance grading. Currently, there are very few AGS Ideal ovals in the market, but they are starting to become available courtesy of a few manufacturers and retailers dedicated to providing diamonds of elite cut quality and beauty. GIA has indicated that they expect to integrate AGS light performance grading more broadly in 2027. It is unknown exactly what that will look like at this time, but it has the potential to be a significant benefit to consumers and bring a range of new diamond shapes to market that are cut for optimal beauty.