ROUND BRILLIANT-CUT DIAMOND : Why Round Diamond Is Best

The round brilliant cut is the only shape that proved to be the perfect pattern for diamond. In consequence, the round diamond became the most popular and accordingly the most prevalent. Scientists, like Marcel Tolkowsky, explain why the round-cut diamond is indeed the most beautiful.

Origin of the Round Brilliant-Cut Diamond

The round brilliant-cut diamond evolved from the triple-cut brilliant. The latter, squarish brilliant proved exceedingly dull for the stone. In fact, the round diamond developed in an effort to solve two problems that came with the old triple cut.

The triple-cut, from which the round-cut diamond evolved

First, there is the ineffectiveness of a squarish outline in bending light back and reflecting it through the surface of the gem. While the English round-cut brilliant, also known as the Old European cut, got this inefficacy out of the way, the latter design did not deal with the other weakness of the old triple cut.

The second problem with the triple cut has to do with the depth. Early versions of the triple cut  were too deep that diamonds lost light beneath the girdle. In answer to this disadvantageous depth, the round-cut diamonds of Europe grew less thick, and therefore more effective in confining light.

The so-called ‘American-cut brilliant,’ for its part, incorporated the most satisfactory angles of the squarish Old Mine cut into a round diamond, and in this manner produced a round brilliant-cut diamond of wider spread and greater brightness and fire.

In either case, the decrease in depth to an optimal proportion, along with the symmetry in facets, unfolded the maximum brilliance of the stone.

It was through this gradual transformation that the round brilliant-cut diamond came to be. When the triple cut reached its perfection, the design became the round diamond as we know it, bearing the faceting of the triple cut yet in a circular outline, thus symmetrical around an axis, and in just the right depth.

Superiority of the Round Brilliant-Cut Diamond

Given its superior brilliance, there is little wonder how the round brilliant-cut diamond rose to popularity, and prevailed since the 1700s over the squarish triple-cut, which thus became the ‘old-cut brilliant.’ An excellent specimen of the round diamond is so effulgent that diamonds of the old triple cut — or other cuts for that matter — appear dull and lifeless in comparison.

Since the arrangements of facets in other patterns do not manipulate light so as to produce the best optical effect, a good round brilliant far exceeds them in both brilliance and play of colors. For example, while the rose cut displays the white brightness of diamond well enough, this pattern fails to effectively disperse light into prismatic colors. In fact, no cut brings out the beauty of the stone so efficaciously as the round brilliant does.

It is indeed no surprise that the round brilliant superseded the rose as the foremost shape for diamonds. Being by far the most effective in unfolding the stone’s natural beauty, the round brilliant is the best diamond shape. The art of cutting reached its perfection in this round diamond.

Hence, so long as the material is thick enough to take the shape of a round brilliant cut, the stone is much better cut in this form instead of any other. Accordingly the round diamond became so prevalent that only in exceptional cases were good diamonds shaped otherwise. Whenever the form and size of the rough crystal permitted, lapidaries always shaped the gem into a brilliant.

Since then, the reputation of the round brilliant as the best diamond shape became firmly established.

Value of the Brilliant-Cut Diamond

There is another reason why the round brilliant-cut diamond became overwhelmingly prevalent. The effectiveness of a cut in bringing out a diamond’s innate beauty greatly determines the price of the stone. Being exceptionally attractive, the brilliant-cut diamond naturally held far higher value. Such value is so high that, though the round diamond involves the most expensive labor and the greatest waste, the brightness and fire that the round brilliant produces more than compensate for the high costs. An excellent round brilliant-cut diamond is simply well worth the cost.

Besides the optical superiority of the round diamond, the huge difference in price ensues from the fact that the rough stone is bound to lose about half its weight in taking the shape of a round brilliant. However, the sheer beauty of the brilliant-cut diamond held even stronger sway further on. By the 1900s, a perfect brilliant-cut diamond of one carat was at least four times as valuable as the rough crystal of the same weight and quality.

The brilliant-cut diamond likewise fetched prices higher than those of other cuts. For instance, in the 1700s, where a rose sold for £6, the brilliant-cut diamond commanded £8 in price. As the brilliant soared even higher in popularity and the rose fell from fashion, the difference in value grew wider. A brilliant-cut diamond was over twice more valuable than a rose.

In fact, diamonds shaped other than in the brilliant cut suffered in value. The Nassak Diamond, for instance, would have held higher value had the 79-carat gem taken the shape of a well-proportioned round brilliant, instead of a triangular Mughal cut, later modified into a mixed cut.

Popularity of the Round Brilliant-Cut Diamond

Among the diamond’s cuts, John Mawe concludes, “The brilliant is deservedly in the highest estimation …” Thus, diamonds most frequently took the shape of a brilliant. It was in this form that the majority of large historical diamonds rose to fame. Even old jewels, including the Kohinoor, were recut to conform to this superior pattern. Indeed, the round brilliant was by far the most  popular and consequently most commonly used shape for the stone.

Ultimately the round brilliant became the only ideal shape for the diamond. Not only for diamonds in fact, but for other transparent stones as well, the brilliant became prevalent. For good reason, too. As Streeter states, the brilliant is the “most effective for all Precious and most of the Semi-Precious Stones.” Hence, colorless stones advantageously received the brilliant pattern, while transparent colored gems also frequently took this shape. The ruby, for example, though sometimes the subject of the step cut, usually receive a brilliant cut. Thus, though not as invariable as in the case of diamond, the brilliant has been a popular pattern widely applied to other transparent gems.

In 1919, an engineer explained through physics how the round brilliant-cut diamond was indeed the most beautiful cut. Marcel Tolkowsky discovered the exact proportions that achieve an optimum balance between reflection and dispersion of light in the round diamond. The 21-year-old engineer also found that cutters had achieved the same ideal proportions even without knowing the mathematics behind them. Relying solely on trial and error, experience and intuition, cutters developed the best diamond shape.

Varying Quality of Brilliant-Cut Diamonds

Though cutters now modeled diamonds after the same cut, the results are not always the same. Not only are there good brilliants and bad brilliants; among good brilliant-cut diamonds, there are those that reflect the most rays of white light and, on the other hand, those that give the most colors. Thus, besides accomplishing the reflection of light through the surface of the gem — instead of losing it through the back as happens in bad brilliants — cutters also have to weigh the reflection of the same light as white brightness against its dispersion into the colors of the rainbow. In fact, an excellent brilliant-cut diamond is a beautiful tradeoff between white brilliance and iridescent fire.

The display of such beautiful combination of fire and sparkle depends greatly upon the accurate distribution of the facets around the round brilliant-cut diamond. For the round diamond to be most effective, its proportion must be perfect, and the series of facets encircling the gem must be symmetrical, the facets thus regular and of the same size.

Indeed, even when the stone takes the supposedly perfect shape of the round brilliant, if the proportions of the gem are bad and its facets not precisely symmetrical, the diamond may still lose so much light instead of reflecting it. Moreover, the round brilliant-cut diamond may sacrifice too much white light to emit different colors or, conversely, give too little iridescent flashes to produce white brightness.

The Ideal Brilliant-Cut Diamond

It was in an effort to make the diamond sparkle even brighter that the facets around the brilliant morphed in angle and consequently in shape. While its 58 facets are essentially the same polished planes from the old triple cut, their shapes shifted in dimensions. The cumulative change has been so radical that the big and small rhombic facets around the table grew into the same size, with their shapes almost triangular. In the end, while the center of the round brilliant-cut diamond was supposed to resemble a star — hence the so-called ‘star facets’ around the table — the resulting design more closely resembles a flower, with bulging petals instead of angular rays.

When accurately executed, the best proportions of the round diamond result in the most beautiful white diamond, exhibiting the greatest refulgence. This truly brilliant diamond now goes by the description ‘ideal cut,’ also known as the ‘American ideal cut’ and ‘Tolkowsky brilliant.’ See also Ideal-Cut Diamond.

Crown of the Round Diamond

The crown is the side of the round brilliant-cut diamond that collects light, as well as the part that ideally reflects it. For this reason, when set in jewelry, the crown — its table and the facets surrounding it – typically faces outward. Thus, when a jeweler mounts the round diamond on its setting, the crown is the part that faces the observer.

Table of the Round Diamond

The round brilliant-cut diamond catches the most rays of light with its broad plane surface at the top. A portion of these rays, estimated at about 17%, instantly bounces off the flat surface, producing immediate external reflection. The rest enters the depth of the transparent gem. Hence, this broad face known as the ‘table,’ along with the rest of the crown, is responsible for capturing the amount of light that makes the round diamond sparkle.

Jewelers generally mount the round diamond on its setting with the broad table facing outward. Hence, the crown is the part of the round brilliant-cut diamond that dazzles an observer with its beauty.

Pavilion of the Round Diamond

The portion of light that reflects from the table, as well as the facets of the crown, becomes part of the luster of a round brilliant-cut diamond. A good polish makes sure that such external reflection effectively happened, while an excellent brilliant cut saw to it that the rest of light, traveling through the depths of the diamond, reflects internally off the rear facets and comes back in the general direction whence it entered. For this purpose, the arrangement and precision of the facets around the round diamond’s lower portion, known as the ‘pavilion’ or ‘culasse,’ are of paramount importance.

The pavilion is the side of the round brilliant-cut diamond implanted in the setting. Hidden from view, this portion of the round diamond serves mostly to intensify the play of light on the surface where people appreciate it.

The depth of the pavilion by itself makes a round-cut brilliant bright. The depth of the round diamond in its lower portion allows the gem to store more light, resulting in increased brilliance. For this reason, a round brilliant-cut diamond is always superior to a lasque, or other thin gems.

However, the shape of its pavilion can make the stone shine even brighter. By preventing light from leaking through the rear and instead sending its rays back through the crown, the lower portion of the round brilliant-cut diamond makes the gem sparkle.

For this purpose, the facets around the lower portion must incline so as to form an inverted cone, which confines the rays of light that travel into the interior of the round diamond by bouncing them off its slanted walls and sending them back toward the top.

Bezel of the Round Diamond

When reflected light hits the table of a round brilliant-cut diamond from beneath, the ray of light passes through the latter, producing desirable reflection on the surface of the round diamond. However, when oblique reflected light lands too far to the side of the gem, the ray of light bounces off the underside of the table and instead leaks through the side of the pavilion. The loss of light renders the round-cut diamond dim. For this reason, cutters trimmed the sides of the crown, thus leaving a bevel along the circumference of the girdle. As a result, the crown of the round diamond consists of the table and the surrounding slope known as the ‘bezel,’ variously rendered ‘bizel,’ ‘bezil,’ ‘bizil’ and ‘beasil.’

The inclination of the bezel allows internally reflected light to pass through its facets, instead of bouncing off and escaping through the sides beneath. Indeed, in the modern design of the round brilliant-cut diamond, light entering through the table bounces out of the lower portion and shines through the crown, whether through the table at the center or the bezel along the sides.

An added beauty brought on by the bezel is the colorful display of the diamond’s fire. Unlike the rose, a skillfully shaped brilliant not only reflects white light, but also breaks it down into the colors of the rainbow. Quite sought after from the round brilliant-cut diamond, such a phenomenon occurs when a ray of light hits the crown at an angle, on which account the light fans out, its colors separating into a spectrum.

To produce these beautiful prismatic colors, exact correspondence of the facets on the crown and those from the pavilion is crucial. All these facets incline at a carefully chosen angle.

Girdle of the Round Diamond

The girdle of the round brilliant-cut diamond is the junction at which the crown and the pavilion meet. As the common base of conjoined pyramids, the girdle is the broadest part of the round diamond, and thus represents the spread of the whole gem. Also known as ‘belt,’ the girdle is the portion fixed in the setting.

In most cases, cutters polished the girdle into a thin ribbon encircling the round brilliant-cut diamond. Sometimes, however, they left the girdle as a ring of sharp edges. This was particularly the practice of English gem-cutters. Thus, the English retailer Harry Emanuel states, “A stone, if well cut, should  have a very thin edge at the girdle …” “Sharp as a knife-blade,” he elaborates.

Though such sharp edges did improve the appearance of the round diamond by enhancing the play of light, these thin edges were liable to chip. On this account, other cutters, particularly those in Holland, simply ground the edges of the round brilliant-cut diamond down to a blunt belt, or rounded them off.

Culet of the Round Diamond

With the top of a rough crystal truncated deep to leave behind the broad plane surface of the table, cutters likewise cropped the opposite end, but to a far less extent. Thus, a small facet caps the nearly pointed bottom of the round brilliant-cut diamond. This tiny plane is the culet — alternately rendered ‘culette’ and ‘collet.’ The collet itself lent its name to the pavilion, which accordingly went by the alternate name ‘collet-side.’

Writers formerly attached exaggerated importance to the culet, and consequently prescribed rigid standards regarding its width and angle. In truth, however, the tiny facet beneath the round diamond does not have an ideal size, but simply came out of precaution to avoid a sharp point. Indeed, as Tolkowsky would have it, the only purpose of the culet was to avoid a sharp point. The function of the culet thus had nothing to do with the round diamond’s brilliance, and more to do with its hardness, or rather its brittleness.  Upon the force of an impact, the tip of a sharp pavilion might cause the brilliant-cut diamond to break or split. For this reason, cutters ground off the bottom point into a small facet, which became the culet.

Hence, while some writers recommended that the culet be a fifth of the table in width, the former occurred far smaller. In fact, cutters often so sparingly cropped the pavilion that the round brilliant-cut diamond almost terminates in a point. When the bottom of the pavilion was blunt enough, there was no need for the cutter to grind any further.

Producing the Ideal Brilliant-Cut Diamond

English cutters were particularly adamant in following the proper proportions of the round brilliant-cut diamond. Unlike those who forewent the right proportions to preserve the diamond’s weight, English artists sought to unfold as much of the stone’s brilliance as possible. Thus, imported brilliant-cut diamonds whose facets incline at an angle of 50° or wider often underwent recutting in Britain. When the refined brightness of the recut gems would fully compensate for the additional cost of labor and weight lost during such an operation, English cutters brought imperfect brilliant-cut diamonds to their ideal proportions.

There were rather few among the most beautiful brilliant-cut diamonds that deviated significantly from ideal proportions. The rest adhered rather faithfully to the standards of the time.

Moreover, the workmanship of European cutters was such that even when they, as John Mawe put it, “trust wholly to the eye,” they still produced excellent brilliants. Indeed, the polishers of the early 1900s made use of no instrument to measure angles and dimensions, but judged of their values entirely by the eye. As Tolkowsky relates of the results, “such is the skill they develop, that if the angles of two pavilions of a brilliant be measured, the difference between them will be inappreciable.”

Disadvantage of the Round Brilliant-Cut Diamond

The sheer number of facets makes the round brilliant-cut diamond the most expensive. With 58 facets in total, the round diamond requires the biggest expenditure of skill, and consequently the highest cost.

Yet the biggest disadvantage of the round brilliant-cut diamond is the weight that the rough stone has to shed to conform to the cut’s proportions. Among the different cuts, the round diamond involves the greatest waste in rough material. Accomplishing the round brilliant’s ideal proportions, furthermore, shaves an even larger volume off the stone. In the 1800s, small diamonds typically lost 38% to 40% of their weight, while bigger stones dropped 50% or even more. Even in the most favorable cases, carving a rough crystal into the perfect brilliant-cut diamond took as much as 52% off the mass of the stone.

The weight of raw material lost in a round brilliant cut consequently reduces a stone’s weight to as little as half, sometimes a third, or even smaller. Even when cutters left the brilliant-cut diamond thick above the girdle, creating the table alone slashed off over a quarter of the octahedral crystal’s height.

Deviation from the Ideal Brilliant Cut

On account of the waste in rough material, there were cases when cutters broke away from the round brilliant’s ideal proportions. Thus, when the cutting of a perfect brilliant-cut diamond involved too much loss in material, lapidaries simply shrugged off applying the exact proportions.

The celebrated Kohinoor from India is a perfect example. The historical gem, which eventually ended up in the English Crown, had already taken the shape of quite a broad gem that to recut the stone strictly in the ideal proportions of the round brilliant entails too great a reduction in weight and size. Thus, departing from the ideal, the Kohinoor became a rather shallow brilliant-cut diamond, too wide for its thickness. Known as ‘spread brilliants,’ brilliant-cut diamonds that lacked depth were comparatively lusterless, glassy, and therefore rather inferior to the rose.

Another consideration that led cutters to ignore the round brilliant cut’s ideal dimensions is the stone’s color. In the case of a pale-colored stone, cutters leave the gem thicker to deepen its hue, while they cut a deep-colored stone shallow to keep the tone lighter.

Inferior Brilliant-Cut Diamonds

In truth, brilliant-cut diamonds did not invariably have the same number of facets. In general, the name ‘brilliant’ refers to the complete pattern, better known in the 1800s as the ‘thrice-formed brilliant.’ This round diamond is the perfect, most complex form, and consequently the most valuable. Indeed, what distinguishes the thrice-formed brilliant from the others is its complete set of facets, at least a series of which the less valuable brilliants lacked.

Once-Formed Brilliant

While the once-formed brilliant keeps the star facets surrounding the broad table at the center, this lesser form lacks the divided cross facets bordering the edges of the round diamond, both on the upper and lower side of the gem. Cutters simply ground the main skill facets on the crown and around the pavilion until they meet at the girdle.

Twice-Formed Brilliant

Like the once-formed brilliant, the twice-formed also lacked cross facets, but only at the top. The pavilion keeps the ring of triangular half facets just beneath the girdle.

Table-Cut Brilliant

A shallow round brilliant that lacked both the star facets and the divided cross facets along the edges was the so-called ‘table-cut brilliant’. This subform of the round diamond is obviously simpler to manufacture. Out of the 58 facets of the full brilliant, the table-cut brilliant displays only 33.

Since cutters reserved the latter pattern for thin diamonds, an excessive width in proportion to its depth characterized this form of the round diamond. In fact, this spread brilliant can be twice wider than it is deep. Such breadth accordingly leaves the gem with a broad table, which must have earned it the name ‘table-cut brilliant.’ Despite its breadth, the crown was still rather thick, as thick as a third of the total depth, whereas the ideal round brilliant only had a fourth of its height in the crown.

Best Crystals for the Round Brilliant Cut

There are natural shapes among diamond’s crystals that are best suited for the round brilliant. The most suitable is the octahedral crystal. Cutters incur much less waste when they fashioned a round brilliant-cut diamond from an octahedron. The contours of this eight-faced crystal closely approximate to the shape of the round diamond, which is basically a truncated octahedron rounded and covered in facets. By simply adding the necessary facets to an octahedron, the raw crystal transforms into a round brilliant. Thus, since the octahedral crystal naturally lends itself to the brilliant pattern, the regular octahedron is the most efficient natural shape for a round brilliant-cut diamond, which accordingly costs less in raw material and labor.

Moreover, since the prevalence of diamond-sawing, the native octahedron became even more viable as a rough material for the round brilliant. Because an octahedron covers a bicone within its dimensions, the crystal may produce two brilliant-cut diamonds, with a smaller round diamond coming from the tip of the crystal sliced off the main gem to make way for the table. Given the further reduction in waste, the octahedron admits of the most efficient brilliant cut.

The dodecahedron is also favorable for this purpose. This twelve-faced crystal similarly involves less labor and waste in taking the shape of a perfect brilliant-cut diamond. In addition, the hexakis octahedron — which resembles the octahedron in general outline but with each octahedral face replaced by six triangles — is likewise a suitable for the round diamond.

On the other hand, cutters cannot so easily transform shapes differing widely from the regular octahedron into brilliant-cut diamonds, especially when the crystals in question are irregular in form. For faceting to proceed, these crystals require much preliminary shaping, if not outright division into smaller fragments good enough for cutting.

Hearts-and-Arrows Brilliant-Cut Diamond

Today, the best form of the round diamond is reputedly the so-called ‘hearts-and-arrows.’  In addition to the ideal proportions of the round brilliant-cut diamond, the hearts-and-arrows exhibits precise symmetry of facets that produce the appearance of arrows on the crown and hearts on the pavilion. The shapes of hearts and arrows do appear on the standard round brilliant, but not as distinctly as they do on an actual hearts-and-arrows diamond.

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About the Author

Jomar Pandan

Jomar ‘Deomar’ Pandan is the author of Power Birthstone. He’s on the fourth draft of a high-fantasy novel, Cybelym, and the first of a historical fiction, Gem Faerie. He hopes to release a nonfiction book about diamond soon. Follow him for updates. Or see his jewelry and designs.

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