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 brilliant cut is built to return light through the crown. Marcel Tolkowsky published the math in 1919, and dealers still reference those proportions at the bench. A standard round brilliant has 57 facets, or 58 if the culet is faceted. The table sits on top. Below it, the crown holds 8 bezel facets, 8 star facets, and 16 upper girdle facets. The pavilion carries 16 lower girdle facets, 8 pavilion mains, and a culet at the point. Each facet angle controls where light exits the stone. Get the angles wrong and light leaks out the pavilion. Get them right and the stone looks alive under store lighting. Round brilliant is the shape. Brilliant cut is the faceting pattern. Princess, cushion, and oval diamonds use modified brilliant faceting on non-round outlines. Same kite-and-triangle logic, different silhouette. Round brilliants command a price premium for two reasons. Rough yield. Cutting a round from an octahedral crystal wastes 40-50% of the original weight. Demand. Over half of engagement ring center stones sold in the US are round brilliants, so cutters optimize production around that shape. GIA grades cut quality from Excellent to Poor on rounds. I've watched buyers ignore cut grade to chase carat weight, then wonder why their 1.00ct looks flat next to a 0.90ct Excellent on the same counter. Cut is the lever most retail shoppers skip. An Excellent cut 0.90ct round at $4,200 can outsparkle a Good cut 1.00ct at $5,800. The faceting style matters more than the outline name on the cert.
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.
Examples
A 1.00ct G VS2 round brilliant with Excellent cut, Excellent polish, and Excellent symmetry runs $5,500-$6,800 at wholesale. Drop cut to Good and the same paper specs can sit $800-$1,200 lower.
A 1.50ct oval modified brilliant at $7,200 next to a 1.50ct round brilliant at $9,400. Same carat, same color and clarity. The round costs more because rough yield is worse and demand is higher.
Princess cuts use modified brilliant faceting on a square outline. A 0.75ct F VS1 princess at $2,400 looks different from a round at the same weight, but both rely on triangular pavilion facets to bounce light back up.
Frequently asked questions
How many facets does a brilliant cut diamond have?
A standard round brilliant has 57 facets, or 58 if the culet is faceted. That breaks down to 33 crown facets (table, bezels, stars, upper girdle) and 25 pavilion facets (lower girdle, mains, culet).
What is the difference between brilliant cut and round cut?
Round cut refers to the circular outline. Brilliant cut refers to the faceting pattern of triangular and kite-shaped facets designed to maximize light return. Most round diamonds are round brilliants, but 'round' describes shape while 'brilliant' describes how the facets are arranged.
Why are brilliant cut diamonds more expensive?
Round brilliants cost more because cutting a round wastes 40-50% of rough diamond weight and because round brilliants dominate engagement ring demand. Cutters charge for lost material, and retailers charge for the shape buyers request most.
Is brilliant cut the same as round?
No. Brilliant cut is a faceting style. Round is a shape. A round brilliant combines both. Princess, cushion, and oval diamonds can also use modified brilliant faceting without being round.