Brilliant Cut
Definition
A gemstone cutting style with 57 or 58 triangular and kite-shaped facets arranged to maximize light return (brilliance) and spectral dispersion (fire). The round brilliant is the most popular diamond cut in the world.
The modern round brilliant cut was mathematically optimized by Marcel Tolkowsky in 1919 to maximize the amount of light returned through the top of the stone (brilliance) while creating rainbow flashes (fire). A standard round brilliant has 33 crown facets and 25 pavilion facets, totaling 57 facets (58 with a culet). The cut's proportions — table percentage, crown angle, pavilion angle, girdle thickness — have been refined over decades and are graded by GIA on a scale from Excellent to Poor. The brilliant cutting style has been adapted to other shapes: oval brilliant, pear brilliant, marquise brilliant, and cushion brilliant, all sharing the same faceting principle of triangular and kite-shaped facets radiating from the center.
Usage in the Trade
The round brilliant cut is the standard for diamond engagement rings and accounts for over 50% of all diamonds sold. Modified brilliant cuts (oval, pear, cushion) are also widely used for center stones and colored gemstones.