Marcel Tolkowsky and the First Ideal Cut Diamond (Specs & Deficiencies)

The man behind the brilliance...

When staring deeply into a diamond, buyers love to admire the colorful dispersion, glistening white flashes, and undeniable brilliance of the world’s most popular gemstone. 👨🏻However, we rarely think about the people behind these cuts or admire the precision required to create an ideal cut diamond.

It’s time to highlight a giant in the industry who produced the initial proportions for the perfect diamond. Marcel Tolkowsky is often referred to as “the father of the modern round brilliant cut”, and his research in diamond cutting laid the groundwork for the “ideal cut” we know and love today.

Marcel Tolkowsky: The Father of Ideal Cut Diamond

Who was Marcel Tolkowsky?

In 1899, Marcel Tolkowsky was born in Antwerp to a renowned family of diamond cutters and dealers. From an early age, Marcel received encouragement from his grandfather, Abraham Tolkowsky, to focus on the more technical aspects of the diamond business rather than be caught up in the commercial facets.

After years of training in his family’s workshop, Marcel attended the University of London to continue his studies. There, he became an accomplished scholar and a brilliant mathematician, physicist, and engineer.👍🏻

A large portion of Tolkowsky’s Ph.D. was spent studying diamond grinding, and he was passionate about finding the ideal dimensions of a diamond. In 1919, he published Diamond Design, a piece that would revolutionize the diamond cutting industry.

Diamond Design detailed Tolkowsky’s scientific approach to diamond cutting with a focus on the reflection and refraction of light. It included a rigorous study of the properties of diamonds and his recommended proportions for an ideal cut diamond, setting a new standard for how brilliant-cut diamonds should be crafted. Today, the fundamentals of Tolkowsky’s dimensions and original thoughts are still used by diamond experts across the globe!

What are the specifications of Tolkowsky’s ideal cut?

So what was included in Diamond Design? And how did it lay the groundwork for the brilliant-cut diamond we know and love today?

After diving into the history of diamond cutting and explaining how light interacts with diamond facets, Marcel Tolkowsky described his mathematical approach to designing the ideal cut diamond, which included hand-drafted ray tracing models as examples.

To achieve an ideal cut, Tolkowsky believed diamonds⁠—particularly round-shaped stones⁠—required 58 facets to maximize their brilliance. There should be 33 facets that make up the top portion of the diamond (crown) and 25 facets on the lower half of the stone (pavilion).

Furthermore, he conjectured the proportions, angles, and interaction between these facets significantly impact a diamond’s fire and brilliance. Here is a breakdown of Tolkowsky’s suggested dimensions:

Diamond DimensionSuggested Measurement (º)
Crown Angle34.5º
Pavilion Angle40.75º
Total Depth59.3%
Table Diameter53%
Crown Height16.2%
Pavilion Depth43.1%

Time and time again, experts verified Tolkowsky’s suggested measurements for optimal lightplay, and the dimensions are still the framework for an ideal cut, round brilliant diamond. With his science-driven approach to diamond cutting, Tolkowsky revolutionized how diamond professionals around the world think about cut as a factor in light performance.

Are there any deficiencies of Tolkowsky’s ideal cut?

In short, yes! While Marcel Tolkowsky’s diamond findings are brilliant, they’re also imperfect. As diamond technology has advanced, more tweaks become necessary to Tolkowsky’s original dimensions to craft the ideal cut diamond. Here are just a few ways experts improved his ideas over time:

Lighting and Scintillation

Tolkowsky’s inability to predict the lighting improvements of future generations played a role in many of the issues discussed below. Modern lighting includes brighter, fluorescent sources that were foreign to the late eighteenth and early nineteenth centuries, which featured candlelight and gas lamps that lit up diamonds from the side rather than the top.

In fact, his works don’t even mention scintillation, which is partly produced by proper lighting and is a critical part of a diamond’s sparkle!

As such, Tolkowsky’s measurements do not suit the electric lighting of offices, homes, etc. The closest we can come to similar lighting is the halogen lights of jewelry stores, which are designed to illuminate diamonds just like candlelight.

However, modifications to Tolkowsky’s dimensions over the decades have vastly improved how these ideal cut diamonds appear under modern-day lighting.

Crown Height

Tolkowsky felt a 16% crown height was ideal for optimal lightplay in a diamond, but again: this was back when candles and gas lamps were primary light sources. Today, a 16% crown height is considered very steep, and this depth actually produces dark shadows in the center of a diamond under modern lighting.

Nowadays, the ideal crown height of a round brilliant diamond can range from 15% to 16.2% depending on the other dimensions of the gemstone. This flexible range means more ideal cut diamonds can be produced, as diamond cutters can work with their source material to produce an “ideal” diamond based on its natural shape.


Despite his detailed measurements for all other aspects of a round brilliant diamond, Tolkowsky actually never discussed proper girdle thickness in Diamond Design. While he does mention it, he never explicitly gives a proper dimension, leading historians to believe he assumed diamonds should have the “knife-edge” style girdle of the time.

A knife-edge girdle is one that is incredibly thin, and it’s no longer used in modern diamond cutting as it’s fragile and tends to chip. As such, later diamond cutters had to account for girdle thickness when applying Tolkowsky’s dimensions, as this measurement can affect lightplay by impacting pavilion percentage, depth, and more.

2D Modeling and Analysis

Obviously, we live in a three-dimensional world.🤹‍♀️ But, Tolkowky’s original models and measurements were two-dimensional, changing the parameters necessary for an ideal cut diamond. Today’s diamond experts utilize 3D modeling and other technology to analyze all 58 facets of a diamond and how they interact with one another. As a result, this allows for more precise dimensions based on each individual diamond’s proportions.

Enhanced technology

Tolkowsky did an amazing job honing in on desirable dimensions for round brilliant diamonds with the technology available to him. However, today, we have many more options for figuring out the proper measurements for all diamond shapes and sizes!

Laser diamond cutting, ASET imagery, CAD software, and other innovations make assessing diamonds a much more exact science, and experts can pinpoint the dimensions necessary for ideal lightplay for each diamond they inspect.

Tolkowsky’s ideal cut vs. Modern ideal cuts

The technology and knowledge surrounding diamond proportions have drastically changed how modern diamond cutters shape these gemstones.🌈 We’ll discuss some major advancements in diamond cutting and how they’ve led to the current ideal cut diamond.

Advances in Tech

Speaking of technology, let’s take a closer look at some of the tools and methods that have transformed the ideal cut diamond since Tolkowsky published his work:

Laser Cutting Technology

Diamond cutters used to painstakingly cut and polish each facet of a diamond by hand, which was an incredibly time-consuming process. Today, these craftsmen cut diamonds with lasers, producing a faster, more precise cut that makes it easier to achieve ideal proportions.

Advanced Light Performance Evaluation Techniques

Diamond professionals and scholars have studied how light moves through diamonds for decades, and two major changes in imaging have revolutionized the industry. Ideal Scope and ASET imaging give gemologists a deeper understanding of each diamond’s lightplay, which helped shape more thorough diamond grading criteria over time.

Ideal Scope Imaging (1970s)

The Ideal Scope uses red reflectors inside a magnifying tube to create a structured environment for viewing a diamond’s light return. Doing so gives the viewer an up-close look at the diamond’s proportions and optical symmetry. To use it, place the diamond’s girdle in line with the bottom portion of the tube and view the resulting colored light within the stone. The results can be read as follows:

Light ColorMeaning
RedBright light returning to the viewer’s eye; there should be plenty of red light for an ideal cut diamond
PinkLess intense light return; not ideal
White or GrayLight leakage; light is exiting the diamond’s pavilion and not returning to the viewer’s eye; too much white is not ideal
BlackLight returning to the eye from very high angles; symmetrical black arrows at the center of the stone indicate a well-cut diamond
ASET Imaging (2005)

Invented by the American Gem Society (AGS), ASET images are used to determine a diamond’s cut grade. The images are produced by utilizing an ASET Scope, which provides a color-coded look at a diamond’s symmetry and proportions. Similar to the Ideal Scope, ASET imagery uses red, green, and blue light to indicate different types of lightplay within a diamond. The colors are interpreted as follows:

Light ColorMeaning
RedBrightest light return; ideal cut diamonds have plenty of red in their ASET images
BlueRepresents areas of contrast, which create patterns of light and dark in the diamond; it should be balanced, symmetrical, and evenly distributed
GreenLess intense light return; ideal cut diamonds show more red than green with a potential for green light at the table of the stone
Black or WhiteLight leakage; ideal cut diamonds have as little black and white light as possible

Computerized Mathematical Analysis

While Tolkowsky undoubtedly did much of his math by hand, today’s diamond experts can rely on computerized technology for more precise measurements and modeling. For instance, ray tracing is extremely helpful for modeling how light moves through a diamond.💻

Additionally, proportions analysis is ideal for measuring the dimensions of a diamond with insane accuracy. These are just a few ways computers have transformed the diamond industry!

Comparing Tolkowsky’s cut to modern day versions

So how do Tolkowsky’s ideal diamond dimensions measure up to today’s ideal proportions? When comparing Tolkowsky’s numbers with those of diamonds graded as Excellent by the GIA (their top grade) and Whiteflash’s A CUT ABOVE stones, the differences are apparent:

GIA Excellent

Well-respected throughout the diamond industry, the GIA takes diamond grading very seriously. As such, their Excellent grade requires a top-notch cut, although they do not have the meticulously graded “ideal” diamond cut offered by the AGS.

When it comes to proportions, the GIA is a bit more lax than Tolkowsky. For example, while Tolkowsky suggested an ideal depth percentage of 59.3% for round diamonds, the GIA approves of a depth percentage in the range of 58.6-64.1%. Similarly, while Tolkowsky said 53% was the ideal table percentage, a GIA Excellent diamond can have a table percentage that is anywhere from 52% to 62%.

The crown angle and pavilion angle of Tolkowky’s ideal diamond proportions are also more precise than the GIA Excellent grade, which uses a range similar to the depth and table percentages.

However, keep in mind that the GIA grades round brilliant diamonds with varying proportions, and so these ranges reflect what would be considered an “Excellent” cut based on each diamond’s measurements as a whole.📊 The GIA does not limit its “Excellent” rating to just one set of proportions, but rather many diamond angles and percentages can add up to an ideal diamond based on light return.

Whiteflash’s A CUT ABOVE

Whiteflash has much stricter grading criteria than most brands for its ideal line: A CUT ABOVE. These diamonds are meant to be the best of Whiteflash’s inventory, and their numbers are more exact than the GIA Excellent scale while still leaving a bit of wiggle room when compared to Tolkowsky’s ideal proportions.

Whiteflash also uses a range for depth and table percentages, which are 59.5-62% and 53-58% respectively. Despite the similarity to the GIA’s range for these criteria, the crown angle and pavilion angle measurements are much more precise and akin to Tolkowsky’s measurements at 34-35° and 40.6-40.9° respectively.

Similar to the GIA, Whiteflash does seem to account for variations in diamond proportions to be more inclusive and allow for more diamonds to qualify as ideal. Again, these numbers all come down to light performance, and each group has their own opinion on what counts as ideal lightplay.

Finally, we’ve included a chart for side-by-side comparisons of each high-grade diamond:

MeasurementsTolkowsky's Ideal CutGIA's Excellent CutWhiteflash's A CUT ABOVE
Slightly Thick
Slightly Thick
Culet-None (Pointed)
None (Pointed)
Polish Grade-Excellent
Very Good
Symmetry Grade-Excellent
Very Good
Crown Angle34.5º31.5-36.5º34-35º
Pavilion Angle40.75º40.6-41.8º40.6-40.9º
In observing the data in the chart, you may notice that both the GIA and Whiteflash require pavilion angles that are 3° smaller than Tolkowky’s original number. This is a good example of how advanced technology has changed what exactly diamond experts view as an ideal cut in light of the precision and symmetry they can now achieve.

Other talented diamond cutters and their contributions to ideal cut diamonds

Marcel Tolkowsky wasn’t alone in his work on ideal cut diamonds, and there are many professionals who have paved the way to our modern perception of the perfect diamond. Here are two other important names to think about when you see an ideal cut diamond:

Gabriel Tolkowsky

Marcel’s nephew, Gabriel Tolkowsky, carried on the family’s tradition and became a world-renowned diamond cutter as well. He was trained by Marcel and his father Jean and went on to conduct in-depth studies of his uncle’s ideal cut proportions, explore new diamond cutting techniques, and optimize the specifications of the modern brilliant cut.

He also worked for De Beers for 20 years, creating the “Flower Cut” they use to improve the light performance of low-quality diamonds and consulting on other diamond cut matters. He also cut the 273.85-carat Centenary Diamond as well as the 545.65-carat Golden Jubilee Diamond, which is the largest faceted diamond in the world!

Brian Gavin

Brian Gavin is a current authority on “super ideal” cut diamonds, as his A CUT ABOVE line falls into that category. He is the co-founder of Whiteflash and created his diamond line in 1998 after rigorous research on the “hearts and arrows” of diamonds and how they impact light performance. Today, he is still a respected scholar among diamond cutters, and his brand of super ideal diamonds continues to change the game of diamond cut.

The brilliant minds behind diamonds

The next time you admire a diamond’s fire, think about the brilliant minds who made it possible! Rough diamonds are far from shiny, and it’s up to determined scientists, engineers, gem cutters, and others to craft the beautiful gemstones we love.💕

Marcel Tolkowsky was a powerful force in crafting the ideal cut diamond, but we’re always learning more about how gems can be cut to perfect their features. If you’re interested in learning more about ideal cut diamonds, visit our diamond cut guide for more info.

Report an Error
linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram