For 105 Years, Marcel Tolkowsky's 'Brilliant Cut' Has Stood the Test of Time

It's been 105 years since a 19-year-old Belgian PhD student at the University of London named Marcel Tolkowsky penned Diamond Design, a book that outlined the perfect mathematical formula for the “brilliant-cut” diamond. Tolkowsky’s accomplishment has stood the test of time and prevails as the most iconic and successful cut in history due to its ability to maximize a diamond’s fire, brilliance and sparkle.

“In 1919, my uncle Marcel unlocked the secret of light within a diamond,” said the late Gabi Tolkowsky during a celebration of the cut's 100th anniversary in 2019. “He figured out how to get the greatest amount of light to shine out of a diamond, calculating the number and arrangement of facets to maximize the light return. This was Marcel’s gift to the world, perfecting the journey of light, giving all those who came after him the knowledge of how to turn a diamond into a unique beauty.”

(Gabi Tolkowsky, one of the world’s most renowned diamond cutters in his own right, died in May of 2023 at age of 83. Marcel Tolkowsky passed away in 1991 at the age of 92.)

Marcel Tolkowsky proved that if a diamond was cut too deep or too shallow, the light coming down from the top would escape out the sides or bottom, resulting in a loss of brilliance. His solution: 57 precisely placed facets cut to exacting proportions so the light coming into a diamond is refracted up through the table and crown to the viewer’s eye.

In Tolkowsky's formula, the crown, which is the upper part of the diamond, would have 33 facets, and the pavilion, which is the conical base underneath the girdle, would have 24 facets. The diamond would also include a tiny 58th facet at the bottom of the pavilion called the culet.

Tolkowsky also suggested that the depth of a round brilliant diamond should be 59.3% of its diameter and that the table facet should be 53% of the total width. What's more, he deemed the perfect crown angle to be 34.5 degrees, and the ideal pavilion angle to be 40.75 degrees.

Of the 4Cs of diamonds — cut, color, clarity and carat weight — cut is arguably the most important. Poorly cut diamonds will likely appear dull or glassy, while a finely cut diamond will appear fiery and alive.

In the 1950s, Tolkowsky's work was further elevated when the American Gem Society adopted his proportions as its standard for grading a diamond's cut.

Even though 105 years have passed since Tolkowsky published Diamond Design, his formula is still considered "ideal" in the world of diamond cutting. Today, Tolkowsky's innovation is called the “American Ideal Cut” or the "Tolkowsky Brilliant.”

Credits: Round brilliant diamond courtesy of Petragems, CC BY-SA 4.0, via Wikimedia Commons. Ideal cut proportions by See page for author, CC BY-SA 3.0, via Wikimedia Commons.