A radiant cut diamond is a diamond fashioned in the radiant cutting style — a 70-facet mixed cut combining brilliant-cut crown facets with step-cut pavilion facets, set within a rectangular or square outline with cropped corners. The cut was patented in 1977 by Henry Grossbard and has since become one of the most commercially significant fancy shapes alongside the princess and the cushion. Radiant-cut diamonds are particularly favoured for fancy-colour stones and for engagement-ring centre stones where buyers want a non-round outline with brilliant-cut light return.

Cut characteristics

The standard radiant has 70 facets: 25 on the crown, 8 on the girdle, and 37 on the pavilion. The corners are cut square or with small chamfers, producing the characteristic clipped-corner outline that distinguishes radiant from princess (which has sharp 90-degree corners). The crown geometry follows the brilliant-cut model with table, star, bezel, and upper girdle facets; the pavilion uses step-cut horizontal facets interrupted by additional facets at the corners and culet area to generate brilliant-cut light return.

Length-to-width ratio is the principal shape variable. Square radiants run from 1.00 to approximately 1.05; rectangular radiants extend from 1.10 to 1.50 and beyond. The 1.10-to-1.30 range is most common in commercial production and tends to be preferred for centre stones in three-stone settings. The choice of ratio is largely aesthetic, though longer ratios show off colour saturation more effectively in fancy-colour stones.

Optical performance

Radiant-cut diamonds produce more brilliance and fire than emerald cuts and conceal inclusions more effectively than step cuts. The brilliant-cut crown breaks up the long open table view that exposes inclusions in emerald cuts, allowing the radiant to face up cleanly at clarity grades that would be visibly included in a true step cut. This makes the radiant a strong choice for buyers seeking a rectangular outline at SI clarity grades, where the equivalent emerald cut would show eye-visible inclusions through the table.

The trade-off is that radiants do not deliver either the dramatic flash of a round brilliant or the architectural calm of a true emerald cut. Their light performance is brilliant-cut in character but the rectangular outline disperses light somewhat differently than the round, producing a slightly more diffuse appearance overall.

Application to fancy colour

The radiant cut is the dominant cutting style for fancy-colour diamonds, particularly fancy yellow and the rarer fancy pink, fancy blue, and fancy brown grades. The combination of long internal light path and multiple internal reflections through brilliant-cut pavilion facets intensifies perceived colour saturation, allowing a fancy yellow stone to face up one or even two saturation grades higher as a radiant than as a round brilliant of the same rough. Most of the famous large fancy yellow diamonds sold at auction in the past forty years have been cut as radiants for this reason — the cut and the fancy yellow grade are closely associated commercially.

In the trade

Radiant-cut diamonds are routinely available in commercial weights from approximately 0.50 carat upward, with strong availability through the standard diamond grading range from D colour to fancy intense yellow and beyond. Pricing follows the standard 4Cs framework; the radiant cut commands no significant premium or discount relative to other fancy shapes in conventional commercial qualities, but high-quality fancy-colour radiants can trade at substantial premiums driven by colour grade rather than cut.

Further reading

• GIA — diamond cut reference
• GIA — the 4Cs of diamond quality
• GIA Gems & Gemology — fancy colour and fancy shape articles