The PriceScope Guide to Tolkowsky Ideal Cut Diamonds
In 1919 a young Belgian math student studying in London, Marcel Tolkowsky, wrote a thesis on the proportions for round brilliant cut diamonds. Tolkowsky got it right and his proportion set is now known as the “Ideal Cut”.
Apparently he asked London passers by to select the most appealing diamond from a small group. From these casual observer opinions, together with those of the diamond cutters in his family’s Belgian business, he confirmed the proportions for the best looking diamonds. His math and physics then proved the observation testing results.
It took 8 decades for the industry to realize that his theorem did not describe just a single proportion but a range of proportions, as first noticed by Mr. Bruce Harding who posts here on PS. Tolkowsky was also aware of a trade off between maximum diamond brilliance and maximum diamond fire that results from varying combinations of crown and pavilion angles.
With thanks to mathematician Jasper Paulsen, you can read Tolkowsky’s entire book here and play with Jaspers mathematic modelling software online. Note that as you thicken the girdle the optimum table size increases, explaining why 57% is really the correct table size for a thin to medium girdle. Tolkowsky did all his math without a girdle – it would have been hard enough in the days before computers and calculators!