Brilliant Cut
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Definition
A faceting style with a circular girdle and triangular and kite-shaped facets radiating from the center, designed to maximize light return and sparkle in round stones.
Detailed Explanation
The modern round brilliant cut has 57 or 58 facets (the 58th being an optional culet at the base). It was mathematically optimized for diamond by Marcel Tolkowsky in 1919, with prescribed crown angle (34.5°), pavilion angle (40.75°), and table percentage (53%). These proportions produce maximum brightness and fire by ensuring that light entering the crown undergoes total internal reflection from the pavilion facets before returning through the crown. The round brilliant accounts for the majority of diamonds sold globally, and its proportions are a primary factor in cut grading.