Who was Marcel Tolkowsky and what did he do for diamonds?
By Jared James · Last updated 21 May 2026
Definition
Marcel Tolkowsky was a Belgian mathematician and diamond cutter who, in 1919, published a mathematical analysis of the round brilliant cut and calculated the proportions that would produce the maximum combination of brilliance and fire. His thesis, Diamond Design, defined specific angles for the crown and pavilion facets that allow light to enter the stone, reflect internally and exit through the top rather than leaking out the sides or bottom. Those proportions became the basis for what is now called the Ideal Cut, and they still underpin modern cut-grading science.
Frequently asked questions
- What proportions did Tolkowsky recommend for a round brilliant diamond?
- Tolkowsky specified a table percentage of 53 percent, a crown angle of approximately 34.5 degrees and a pavilion angle of 40.75 degrees, with a total depth of about 59.3 percent. Modern ideal-cut definitions have been refined through further research and computer modelling, but they remain close to Tolkowsky's original values.
- Is the Ideal Cut still based on Tolkowsky's work?
- Yes, Tolkowsky's analysis provided the scientific foundation for the Ideal Cut concept, and his values are still the starting reference for most discussions of optimal round brilliant proportions. Organisations like AGS developed their formal Ideal cut grade directly from his work, and GIA's Excellent grade also reflects similar proportions.
- Who was Marcel Tolkowsky?
- He was born in Antwerp in 1899 into a prominent diamond-cutting family, studied engineering in London, and published Diamond Design as part of his engineering degree. He later worked in the diamond trade in the United States. His family background in cutting gave him practical knowledge to complement his mathematical approach.
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