The modern round brilliant cut diamond was created in 1919 by Russian mathematician Marcel Tolkowsky after extensive research on reflection and dispersion of light in diamonds. In his honor, round brilliants are sometimes referred to as the ‘The Tolkowsky Cut’.

The round brilliant cut diamond is the most popular diamond used in the diamond industry today. Engagement rings with this shape are very popular, with countless designs that exist and yet more in progress.

The Secrets of the Round Brilliant Cut Diamond

The round brilliant cut is the most celebrated of diamond cuts. For centuries, diamond cutters have sought to achieve round diamond with perfect brightness. However it wasn’t until about 100 years ago that someone found a way to achieve this idea.  Before we begin, here is an overview of diamond vocabulary. Every aspect and angle of the stone has a name, all of which are referenced in articles and trade publications. By learning these terms, you will help gain a better understanding and appreciation for the jewels you admire.

There are three names for the light that reflects from a diamond. Brilliance is the term for the flashes of white light that shine from the top of a jewel. Fire is the spots of color that emerge when white light separates into the different hues of the rainbow. Scintillation is the interchange of light and dark spots in the crystal. A well cut diamond will have a fine balance of these three phenomena.

From top to bottom, a diamond’s anatomy begins with the table. This is the facet that forms the highest part of the stone. Flanking the table and angling downwards are the star facets, while kite facets are nestled in between the stars. Upper girdle facets, as the name implies, ring the upper edge of the girdle, or outermost perimeter of a diamond. Everything from the table to the upper girdle facets make up the crown, or top of the diamond.  Immediately below the girdle are the lower girdle facets. In between the lower girdle facets stretch the pavilion facets. At the very bottom of a diamond may be a culet. Together, these three facet types make the pavilion, or lower portion of a stone.

The round brilliant diamond with its complex anatomy was born in 1919. A PhD student and member of a long line of jewelers named Marcel Tolkowsky published a 104 page paper titled “Diamond Design.” It was the culmination of careful research and intricate calculations on how to make diamonds their most beautiful. By following precise ratios and shape, a diamond could take in and reflect an optimal amount of light.

As influential as “Diamond Design” was, other jewelers have sought to improve upon the round brilliant diamond. One addition was to add facets to the girdle. Marcel Tolkowsky’s calculations used a very thin girdle prone to chipping that didn’t add light to the jewel. Likewise, jewelers of today sometimes add a culet to discourage accidental breaking.  While proportion is crucial in creating optimal lighting in a round brilliant, there are differing opinions on how to achieve it. The Parker Brilliant guidelines for example, calls for a crown that makes 10.5% of the diamond’s height, a pavilion depth of 43.4% and a table diameter of 55.9%. Compared to the American Standard of a 16.2% crown height, 43.1% pavilion depth and 53% table diameter, the Parker Brilliant doesn’t shine as strongly. The Accredited Gem Appraisers offers flexibility with their recommended ratios, suggesting a 14.0–16.3% crown height, 42.8–43.2% pavilion depth and 53-59% table diameter.

Today’s round brilliant cuts are often made of 57 or 58 facets. Along with a single table facet, the crown contains eight star and eight kite facets as well as sixteen upper girdle facets. Pavilions contain sixteen lower girdle facets and eight pavilion facets, with an optional culet. The number of facets on the girdle varies, and isn’t included in the total facet number.  Other round brilliant modifications focus on changing the number of facets. One variation patented in 2008 uses 81 facets, dramatically increasing the number of pavilion facets. On the crown, kite facets are replaced with upper and lower bezel facets. The result is a dramatic change in how white light travels within the stone.  Another notable variation on the round brilliant cut is the hearts and arrows effect. Strict adherence to proportion creates rings of hearts and arrows within a diamond when it’s placed into a special viewer. Some companies proclaim heart and arrows style diamonds to be the best form of round brilliant, though the statement is subjective.

There’s no consensus as to what makes a perfect round cut brilliant diamond. While many acknowledge the importance of ratios and proportions, there’s a range of standards and cutting styles. There is a wealth of round brilliant cut diamond styles for collectors to enjoy, from the classic 57 facets to those that produce unusual shadows or flash. The future will likely produce more variants for connoisseurs to admire.

Specifics of the Round Brilliant Cut Diamond

In 1919, Marcel Tolkowsky wrote of specific measurements that would create diamonds much brighter than any diamond cuts before. His ideal round brilliant cut diamond has a 16.2% crown height, 43.1% pavilion depth, 53% table diameter, and a 34.5-degree crown angle. It features 57 facets, made of 1 table, 8 star, 8 kite, 16 upper girdle 16 lower girdle and 8 pavilion facets. There is no culet and the girdle is very thin and unfaceted. Tolkowsky’s diamond cuts and proportions serve as the basis for the American Standard round brilliant diamond, which is commonly used in North America.

Since his publication of “Diamond Design,” other gemologists have tried to improve upon Tolkowsky’s work or provide their own idea of what makes a round brilliant cut diamond. 1929 saw the advent of the Ideal Brilliant, which called for a 19.2% crown height and a 41.4-degree crown angle. Other variations throughout the years, including 1939’s Practical Fine Cut and 1968’s Eulitz Brilliant use subtler changes in angle, height and proportions from Tolkowsky’s work to create optimal shine. Independent grading labs such as the Gemological Institute of America believe that a number of standards have the capacity to become excellent grade diamonds.

A number of round brilliant cuts hew closely to Tolkowsky’s proportions while adding strict devotion to symmetry and polish. Other styles, such as the passion cut, play with faceting and proportion to create a round brilliant cut diamond that are both bright yet different from the 1919 recommendations. Diamond cutters continue to experiment, striving for new ways to make a beautiful diamond.

How a Round Brilliant Cut Diamond is Certified

When buying diamonds, people want the best they can afford. With a cut as complex as the round brilliant cut diamond, it can be tricky for a layperson to tell what makes one stone higher quality than another. Independent laboratories such as the Gemological Institute of America (GIA) certify diamonds according to strict standards, giving manufacturers and connoisseurs peace of mind.

Each diamond arrives at GIA in a plain case to ensure that its provenance or packaging doesn’t influence the technicians. Diamonds are graded by the four Cs; carat, color, clarity and cut. Carat measures the size, weighing a jewel to the nearest ten thousandth of a carat. Color helps to determine how strong of a tint a diamond has, be it a subtle yellow, noticeable brown or completely colorless. Clarity catalogues the types of blemishes and inclusions on any one diamond, and marks these characteristics on a diagram.

Of the four Cs, cut is the most complex to grade. The diamond is divided into its individual components, like the girdle, crown, pavilion and table. These portions are compared to the jewel’s total height to determine if the proportions are at an ideal ration for allowing light into the jewel without leaking. The number and placement of facets are considered in relation to one another, and how well they reflect light within the stone.

Once a jewel is evaluated, it’s assigned a report detailing its dimensions, 4Cs, polish and other notable factors. Each diamond also comes with a diagram outlining the placement and type of inclusions, recording a jewel’s “fingerprint” for later identification. People looking for a new diamond should feel free to ask their jewelers for certified diamonds and a copies of the reports to better understand the diamonds they’re buying.

Hearts and Arrows

Since the creation of the first Round Brilliant diamond in 1919, many jewelers have added their own variations on the cut, increasing facets or enhancing brilliance. In the 1980s, Japanese artists created an optical trick that created rings of hearts and arrows in diamonds cut in specific proportions. There are even specially designed viewers that allow retailers and customers to see the Hearts and Arrows through a stone’s table and pavilion.

Many organizations tout this type of diamond as the pinnacle of round brilliants. While independent grading labs have found that these stones often have strong symmetry and high polish, there are no standards as to what qualifies as Hearts and Arrows. Though many of them have facets and angles that indicate a beautifully cut diamond, its best to ask for the jewel’s cut grade to make sure.

Journey to the Round Brilliant

The round brilliant cut diamond is not the culmination of centuries of innovation so much as step in the quest to make the brightest diamonds. In the earliest years of diamond jewelry, the stones were admired for their hardness and luster rather than their internal brilliance. Between diamond’s supreme hardness and limited technology, the earliest diamond cutters concentrated on cleaning the rough and evening its sides. Diamond rings from the Roman Empire show octahedral rough mounted in gold.

During the Middle Ages, advances in technology allowed workers to facet diamonds into square and rectangular cuts with broad table facets. These jewels were better at reflecting light on their surfaces than inside the stone, though their interiors remained dark. It wasn’t until the 1700s that diamonds started brightening. Pavilions deepened, and shapes went from square to what are now called cushion cut diamonds.

Though cushion cut diamonds were popular through the 18th and 19th century, the brilliance of these early diamonds weren’t consistent. The desire to preserve carat weight often took precedence over symmetry and proportion. It wasn’t until 1919 that the round brilliant cut diamond that we know today appeared. The original round brilliant cut diamond standards called for and exact number of facets placed so on the diamond, careful symmetry and proportions to create an optimal amount of light.

Others have built upon the ideas of the round brilliant cut diamond, honing its ratios and creating yet stricter standards, or altering the number and placement of facets. Some jewelers have experimented with brilliance in fancy shapes such as pear cut diamonds, princess cut diamonds and radiant cut diamonds. The search for peak diamond brilliance is ongoing, with many approaches rather than a single path.

Round Brilliants and the Four Cs

The round brilliant cut diamond made its debut in the early 20th century. While earlier diamond cuts aimed for brightness, the round brilliant aimed for careful proportioning and symmetry, giving light the best possible environment in which to make the jewel shine. Not only do cutters facet a round brilliant just so in order to bring out its best qualities, they try to preserve as much of the carat weight as possible while masking less desirable clarity characteristics. After cutting, the type of mount for the diamond may be chosen to highlight or disguise the jewel’s color.

The larger the diamond, the rarer and more valuable they become. Magic sizes, the carat weights which cause a diamond to jump in value, are emblematic of this trait. While diamonds are cut to bring out their beauty, excessive cutting may lower a stone’s value. At the same time, an unbalanced stone that doesn’t adhere to desirable depth and proportions are less aesthetically appealing and less desirable than a bright jewel. Diamond cutters must be careful to fashion stones that have wonderful brilliance while sacrificing as little of the diamond as possible.

Many diamonds have quirks inside their crystal or on their surfaces, known as clarity characteristics. Some occur during handling, like chips on a girdle, others during the cutting process, like polish lines, and still more while the diamond was being formed, such as a foreign crystal encased in the jewel. Drastic clarity characteristics may interfere with the durability of a diamond, while subtler quirks may influence the jewel’s brilliance.

Few diamonds are born in a vacuum. A large quantity of naturally formed diamonds are influenced by their surroundings, which can color the jewels. Most diamonds have a yellow or brown tint to them, a result of nitrogen mixed into their crystal structure. The shading is often subtle, though lighter diamonds are rarer and more sought after.