Round Cut Diamond Buying Guide

Round cut diamonds, also known as round brilliant or circle cut diamonds, have long been the most popular diamonds in terms of shape. There are a number of reasons for this popularity from both an economic as well as light performance perspective. Round brilliants can be cut efficiently from the most common types of natural rough diamond crystals. Therefore the cutter can extract a good yield of finished polished diamonds from a given rough. This holds costs down and enables the diamonds to be sold more affordably. Secondly, the symmetrical configuration of the standard 57 facet round brilliant is such that, if cut to proper proportions, can produce a diamond that reflects and refracts light with dazzling performance. When crafted with precision round cut diamonds are unmatched in brilliance, fire and scintillation.

*Note: This article pertains largely to natural diamonds. Much of the information applies also to round cut lab grown diamonds, with some differences that will be discussed below. 
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What is a Round Cut Diamond?

The modern round brilliant has a standard basic facet pattern of 57 facets, (or 58 if the culet has a facet on it). There are 8 main facets on the crown and eight mains on the pavilion. The pavilion and crown each feature 8 pairs of half facets between the mains. The crown also has eight small ‘star facets’ and one large facet on top call the table facet. The pavilion sometimes includes a small facet on the culet. All these facets, the mains and the ancillary facets, must work in full harmony in order to produce the spectacular sparkle that can be seen from across the room.
Round Diamond Anatomy
A beautifully crafted diamond is like a tiny sculpture of mirrors designed to reflect and refract light back to the eye of an observer in a light show of brilliance, fire, and scintillation. No other shape quite matches the round in its potential for pure optics and light performance.
Round Diamond Virtual Facets

Early Round Cut Diamonds

The earliest diamonds were fashioned with primitive tools at a time when it was only possible to place a few rudimentary facets on them. Because the most common diamond crystal is octahedral in shape, the easiest way to cut them was to grind down the points to form a large table on one end, a small culet on the other, and round out the corners. This resulted in the “old mine cut” diamond which was more rectangular than round, and an inspiration for the cushion cut. Over the years the round cut diamond was further refined with the addition of more facets to become the ‘old European cut’, the predecessor to the modern round brilliant.
The venerable Round Brilliant diamond remains by far the most popular diamond cut of all. So much so that the gem itself is identified by this iconic shape. It is a timeless classic that is always in style and has been for hundreds of years. Because of its symmetrical geometry, a well cut round diamond has the greatest ability of any shape to maximize light performance. The A CUT ABOVE® Round Hearts and Arrows Super Ideal Diamond, with proven optics of the highest order exemplifies the extraordinary potential of the round brilliant.

American Ideal Cut – A History of Diamond Cutting in the US

The Belgian mathematician Marcel Tolkowsky is generally credited with being the first to scientifically calculate the proportions that best unlock the fire and brilliance of round cut diamonds. However, it turns out that American cutters were cutting to very similar proportions decades before Tolkowsky published his thesis
In order to cut to what have become known as “Tolkowsky” proportions, more weight is generally lost in the cutting process. And because cutters were strongly motivated by the longstanding practice of cutting for weight over beauty, the Americans pioneering the Ideal Cut were unable to spread their philosophy to the broader market. To illustrate how powerful the status quo is in the diamond industry, even today - over a century later - ideal cut round diamonds are still underrepresented in the market.
For more on early American diamond cutting we recommend Al Gilbertson’s fascinating book on the subject called American Cut – The First Hundred Years.

Laboratory Cut Grading – The Big Breakthrough

Prior to the advent of laboratory grading of cut quality, there was little way for a consumer to assess this most important of the 4 C’s. Until 1996, no major laboratory (including the biggest –GIA) provided an overall cut grade on diamond reports. Dimensions, proportions, polish and symmetry were reported, but no overall cut grade. Most trade professionals did not know how to grade cut, so the expectation that a consumer would have this ability was completely unreasonable. Yet, as the information age dawned, more consumers were taking an interest in developing their understanding. To address this need the American Gem Society set up their own laboratory in 1996 for the purpose of adding cut grading to lab analysis of the other 3C’s- color, clarity and carat (weight). The demand for their reports was robust, validating their belief that cut grading must be a fundamental part of any laboratory report that fully educated and protected the consumer. It would be another decade before GIA would add a cut grade to their reports. And in the meantime, AGS Laboratories (AGSL) transformed their cut grading system from a two dimensional construct based around Tolkowsky proportions, to a 3D light performance based system involving sophisticated light ray tracing.
In 2006 the GIA finally launched their cut grade system with a top grade of Excellent. While their system is more simplistic and broad, the market quickly embraced the GIA system. Manufacturers now geared their production to align with parameters that would achieve a high cut grade at GIA while still yielding as much carat weight as possible. While critics will argue credibly that the GIA Ex grade is overly broad and contains some diamonds with less than outstanding light performance, in general diamond cutting took a huge step forward almost immediately upon GIA rolling out their cut grade system.
While some GIA Excellent diamonds are in the sweet spot of cut quality, others fall well outside. When analyzing a GIA Ex it is therefore necessary to see additional diagnostics in order to identify top performers. Whiteflash provides advanced imaging on our in-house inventory of fully vetted GIA Triple Excellent diamonds in our Premium Select category. For a further comparison of grading at the two top tier gemological laboratories please see our article AGS vs GIA.

The Rise of Ideal Cut Diamonds

AGSL made a name for itself in the diamond industry by pioneering cut quality analysis, and adopting rigorous standards for their grade of Ideal, also known as AGS 0. Cutters who were cutting for beauty began sending their production to AGSL in order to have documentation that better communicated to consumers that they were buying a diamond of elite cut quality and light performance.
Diamond Cut Graph

Hearts and Arrows Diamonds

During this time of heightened interest in ideal cut diamonds, experts in Japan were also obsessed with cutting diamonds to a level of optical precision that would result in exacting Hearts and Arrows facet reflection patterns. They developed tools for viewing these patterns in what is now known as the Hearts and Arrows viewer. Eight arrows are seen through the table, and eight hearts are seen through the pavilion. Cutting diamonds to this level of accuracy was only done by specialized manufacturers and the skill and time required to do so added to their exclusivity. It was not until the benefits of hearts and arrows diamonds started to be understood that more cutters took an interest in devoting the required resources to cut them.
A CUT ABOVE Hearts and Arrows Round Diamonds

Modern Diamond Cutting - The Era of the Super Ideal

The philosophy of cutting for beauty over carat weight that was started by Robert Morse and his American colleagues in the late 19th century, never really disappeared. Many diamond enthusiasts and experts were enthralled by the difference in light performance that precision cutting could make to the overall optics and beauty of the round cut diamond. Ultimately it was the Japanese who seized on perfect optical symmetry and what we now call “hearts and arrows” as the first standard for the super ideal cut diamond.
Despite the stringent standards required to achieve the light performance based grade of Ideal by AGSL, optical precision such as results in perfect hearts and arrows patterning is not one of the criteria. The ray tracing algorithm evaluates brightness, contrast, fire and leakage but does not factor in patterning. It is not that AGSL thinks that patterning is irrelevant, but it does not have to be ultra-precise in order to perform within the top category by their objective metrics. Thus, there is a quality above ideal, that requires ideal as a baseline, and perfect optical precision (hearts and arrows) as an additional qualification. This is the essence of the concept of the “super ideal”.
Super Ideal Cut Diamonds
A CUT ABOVE® Super Ideals (ACA) in relation to GIA EX and AGS Ideal

Diamond Analytics and Advanced Imaging

Diamond cutting today is highly sophisticated ultilizing computerized tools and analytics that enable experts and consumers alike to understand minute details of cut craftsmanship and light performance. The leading jewelers today are providing this information to their clients in order that they may make fully informed buying decisions.
Diamond Imaging
Whiteflash is a leader in consumer education and provides a full set of diagnostics including advanced light performance images on all our in-stock diamonds. For a purchase as important as a diamond engagement ring, consumers are well advised to shop with merchants to understand the technical details of diamond grading and have deep expertise in diamond light performance.

Diamond Fluorescence

Approximately 30% of natural diamonds will glow in response to intense ultraviolet light; a property can normally only be observed in a darkened room with a black light. Of this 30% the vast majority emit a blue light. Fluorescence is primarily an identifying characteristic and not a performance characteristic. Many people find this hidden property to be very alluring.
However, there are also those who eschew fluorescence for a variety of reasons. Because fluorescence can impact pricing and liquidity, in some cases significantly, it is important for a shopper to become acquainted with the pros and cons of fluorescence. In this way you can make a sound decision on the diamond that is right for you. For more on this remarkable property please see our article Diamond Fluorescence – Good or Bad?

Round Cut Diamond Pricing

Natural diamond prices tend to follow the same laws of supply and demand that other product do. Because each diamond is a unique entity with a unique combination of qualities, the level of supply tends to revolve around the specific rarity factors including all the 4cs. The more colorless and flawless a diamond is, the rarer it is. And the more precise the cut, the rarer a diamond is because it takes more skill and time to cut ideal and super ideal diamonds. Interesting, certain levels of quality in color and clarity do not correspond with significant improvements in a diamond’s appearance but do increase their rarity and thus their price. For example, diamonds in the VVS to FL range (four distinct qualities) look the same to the naked eye. It is only possible to make grade determinations under a microscope. Similarly, colors in the DEF range are all considered ‘colorless’ and only an extremely discerning eye can tell the difference. Yet those laboratory determinations can impact the price considerably.
Diamond Price Graph
Likewise, a diamond with a lab certificate of Ideal, or a branded super ideal diamond (with proper supporting evidence) can be expected to trade for a higher price, all other aspects being equal. It is easy to see why this would be the case when you look at the extensive list of specifications and qualifications that must be met for a brand like the extraordinary A CUT ABOVE® super ideal.
Natural diamond prices often fluctuate and are impacted by many factors. While historically prices have gone up giving many people the notion that investing in diamonds makes sense, diamond prices can also fall. World events, supply chain issues, and international economic growth can impact the demand for diamonds.
That said, a natural diamond is a very rare resource found in only a few places in the world. The geological events that led to the miracle of their formation billions of years ago, and their transport to the surface of the Earth from 25 miles below the crust, are indeed exceedingly isolated events. Diamond mines are being depleted faster than new ones are being discovered. This would clearly suggest that diamonds will continue to be in short supply for years to come. And if demand remains strong or grows, it would be logical to anticipate increasing prices in the future.

Round Cut Lab Grown Diamonds

Lab created diamonds have emerged as a very popular option for consumers in today’s market. The cost of lab grown diamonds is significantly less than natural, giving consumers a wider range of diamond options to choose from than ever before. And high quality well-cut lab diamonds can be just as beautiful as natural diamonds as they have essentially the same optical and physical properties.
Round cut lab created diamonds are still the best sellers, but due to the affordability of the rough, shoppers are taking “flights of fancy” with other shapes as well. Because lab grown diamond rough does not have intrinsic rarity and is modestly priced, there is no imperative for cutters to focus on what shape will result in the best carat weight yield, so a wider range of shapes are in play. And there is no real incentive for cutters to take compromise cut quality for small gains in carat weight, so they have more freedom to cut for beauty. Because of these fundamental differences between natural mined diamonds and lab grown diamonds, there are more options available today for affordable and beautiful diamonds. But for maximum light performance round cut lab grown diamonds are ideal, just as rounds are optimal in natural diamonds.
For those researching round cut lab diamonds, all of the cut quality considerations outlined above still apply, and laboratory certification from a top tier gemological lab such as IGI and GIA is still highly recommended. To have full peace of mind with any diamond purchase, a thorough understanding of the stone is a must.

Best Settings for Round Cut Diamonds

In addition to the brilliance and fire of a fine quality precision cut round brilliant, probably the best thing about them is the incredibly wide range of setting styles available. Because somewhere in the vicinity of 80% of all diamonds sold are rounds, for decades designers have been creating beautiful works of art for round cut engagement rings. In the case of designer A. Jaffe, for over a century!
There are many generic designs carried by jewelers all over the world such as the classic solitaire style that have been in the public domain for decades. And then there are unique styles that are the intellectual property of designer brands who created them and who enforce their claims of exclusivity. It is unethical for any jeweler to copy those designs, though trademark infringement remains a significant problem in the industry. Consumers should be wary of any jeweler willing to copy a designer style as it is a form of piracy that reflects upon the jeweler’s honesty and integrity.
Simon G. MR1394 Fabled Diamond Engagement Ring
Simon G. MR1394 Fabled Diamond Engagement Ring
Tacori 2620RDP Dantela Crown Diamond Engagement Ring
Tacori 2620RDP Dantela Crown Diamond Engagement Ring
Ritani 1RZ2490 Micropave Diamond Engagement Ring
Ritani 1RZ2490 Micropave Diamond Engagement Ring
Authentic designer brand engagement rings are manufactured to the high standards of each brand, and come with various guarantees and benefits. A consumer is assured a consistent, high quality product and a company that has a significant incentive to stand behind the product in order to protect brand reputation and value. While they tend to be more expensive, there are many reasons to opt for a genuine designer style from an authorized retailer. The emergence of lab grown diamonds in high quality and at very affordable prices has given many shoppers the opportunity to get both a fine designer ring and a sizeable and beautiful diamond at a total price that stays within budget.


Round cut diamonds, and especially round cut engagement rings, are the top sellers in the jewelry industry. No other diamond shape is capable of more fire and brilliance when properly crafted. Diamond cutting has dramatically improved in recent decades due to laboratory developments and technology. Diamond analytic tools and light performance imaging now let consumers get a full picture of a diamond’s optics and are especially indispensable for online shoppers today.
Diamonds come in many beautiful shapes and forms, but none has been more revered through time than the venerable round cut diamond ring.

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