Cut registry › Jewellery cuts › Radiant
Jewellery cuts · Square brilliant
The hybrid.
The radiant was invented to put a brilliant’s light inside a step cut’s outline. It succeeds, and it is also the shape on this site where proportions matter most.
The short version
A radiant cut diamond is a square or rectangular stone with truncated corners and brilliant-style faceting throughout, typically carrying 70 facets.
It was designed to combine the outline of an emerald cut with the light return of a brilliant, which makes it the only true hybrid in common production.
Definition
Henry Grossbard developed the radiant in 1977, working on a problem the trade had not solved: rectangular diamonds looked elegant but returned comparatively little light, because step faceting is not designed to return it. His answer was to keep the cut-cornered rectangular outline and replace the step facets with brilliant ones.
The result behaves like a brilliant and looks like a step cut from above. Its many small pavilion facets scatter light into a continuous glitter with no readable pattern, which the trade calls crushed ice. That is the opposite of the princess, where a well-cut stone shows a distinct X through the table.
Two practical consequences follow. The cut corners make a radiant substantially more durable than a princess, which has no protection at its four points. And the faceting concentrates body colour, which makes a radiant superb for fancy yellows and a liability for white stones, where it shows warmth sooner than an oval or a round would.
Proportions
Commonly cited ranges against our measured reference stone. Read the note below the table before reading the light figures: this is the one shape here where our reference geometry sits well away from a well-cut market stone.
| Measure | Commonly cited | Our reference stone | What it does |
|---|---|---|---|
| Length-to-width | 1.00 to 1.05 square; 1.15 to 1.35 elongated | 1.28 | Both are common and neither is standard. |
| Depth | 60% to 70% | 53.8% | Above about 70% the stone reads smaller than its weight. |
| Table | 60% to 70% | 50.5% | The flat top, as a share of the width. |
| Pavilion angle | not commonly published | 30.3° | Shallow here, and that is what the figures below reflect. |
| Facets | 70 | 60 | Counted as facets that actually reach the surface. |
A caveat we would rather publish than bury. Our reference radiant carries a pavilion angle of 30.3°. In diamond, total internal reflection needs 24.4° of clearance, and a pavilion this shallow sends a great deal of light straight out of the bottom of the stone. The figures in the next section are therefore a measurement of this geometry at these proportions, and not a verdict on radiants as a class. A radiant cut to a proper pavilion angle will not read like this.
Light
Measured on the census that runs on every cut on this site: 3,200 rays face-up, 2,200 at 20° tilt, on exact facet geometry, against T57 as the standard.
| Material | Useful light | Leak | Fire | Scintillation | Global | vs the standard |
|---|---|---|---|---|---|---|
| Diamond | 31.55% | 41.49% | 76.55 | 73.64 | 65.14 | −23.46 |
| Moissanite | 33.18% | 36.68% | 91.66 | 73.64 | 69.20 | −20.62 |
| Cubic zirconia | 33.18% | 46.75% | 90.97 | 73.64 | 68.06 | −23.72 |
| T57 standard, diamond | 92.28% | 1.88% | 78.85 | 71.82 | 88.61 | 0.00 |
Our reference radiant returns 31.55% of entering light usefully and leaks 41.49%, against the standard’s 92.28% and 1.88%. That is the weakest light return of any jewellery cut we publish, and it is a direct consequence of the shallow pavilion noted above rather than of anything intrinsic to the radiant design.
We are publishing it because it makes the usual depth advice concrete. Guides tell you a shallow radiant looks spready and a deep one looks small. The measured version is blunter: on a radiant, shallow is not spready. It is leaky. More than a third of the light entering this stone leaves through the bottom, where nobody can see it.
One figure here must not be read as a virtue. The radiant’s tilt retention reads at the scale’s ceiling of 100, but tilt retention is a ratio of what survives to what was there to begin with. On a stone returning 31.55% face-up, holding all of it under tilt means there was little left to lose. Take it as an artefact of a low baseline, not as stability.
Variants
The library carries both an elongated radiant and a square one, and the contrast makes the caveat above concrete rather than theoretical.
| Geometry | Facets | Useful light | Leak | Fire | Global | What differs |
|---|---|---|---|---|---|---|
| Radiant on this page | 60 | 31.55% | 41.49% | 76.55 | 65.14 | The reference stone every other figure here describes. |
| Square radiant | 49 | 72.42% | 12.37% | 62.12 | 76.82 | The square version, and a proper pavilion angle. It leaks a third of what the elongated reference stone does. |
Same family, same faceting idea, and a pavilion angle that actually works. This is what the warning above means in practice: the difference between these two rows is almost entirely one angle, and no grading report records it. The square radiant has its own page.
Against the standard
Light return. 92.28% for the round against 31.55% for our reference radiant, with the pavilion-angle caveat above attached to that comparison.
Sparkle character. 60 facets against 57, giving 73.64 on scintillation against 71.82. Its character is a continuous crushed-ice glitter rather than the round’s readable pattern.
Colour. The radiant concentrates body colour where a round disperses it, so a white radiant usually needs a higher colour grade than a round of the same size. In a warm metal, H or I is generally safe, because the setting masks what the stone concentrates.
Durability. The truncated corners make a radiant the most robust of the square-ish brilliants, and considerably safer than a princess.
Clarity. The crushed-ice scatter hides inclusions well, so a radiant is forgiving where an emerald cut is not.
Price. Generally less per carat than a comparable round, because the shape retains more rough.
The baseline for all of this is the round brilliant itself. Its facet plan is set out in the anatomy of a round brilliant, and the measured standard we compare against is T57, the stone Tolkowsky published in 1919.
Materials
In moissanite our reference radiant returns 33.18% for 69.20 Global. Moissanite has a higher refractive index than diamond, so its critical angle is smaller, and a shallow pavilion costs slightly less in it than in diamond: the leak falls from 41.49% to 36.68%.
In cubic zirconia it returns 33.18% for 68.06 Global, leaking 46.75%. Zirconia’s lower index means an even larger critical angle, and the shallow pavilion costs more there than anywhere else. That progression is the clearest illustration on this site of why a facet plan has to be drawn for the material it will be cut in.
Watch it happen for this shape in the Index.
Trade-offs
Questions
The questions buyers actually ask, answered in full. Where the answer is ours to prove, the figure is measured on the Index; where it is an established gemological fact, it is stated as one.
A radiant cut diamond is a square or rectangular stone with truncated corners and brilliant-style faceting throughout, typically carrying 70 facets. Henry Grossbard developed it in 1977 to give a rectangular diamond the light return of a brilliant rather than of a step cut.
Corners and pattern. A radiant has cut, truncated corners, which makes it markedly more durable; a princess has sharp corners that sit on cleavage planes and chip. Optically a well-cut princess shows a readable X through the table, where a radiant produces a continuous crushed-ice glitter with no pattern at all.
Usually higher than for a round of the same size. The radiant’s faceting concentrates body colour rather than dispersing it, which is exactly why it is the preferred cut for fancy yellows and exactly why a white radiant shows warmth sooner. In yellow gold, H or I is generally safe because the metal masks what the stone concentrates.
Commonly cited as 60% to 70% for both. Depth above roughly 70% makes a radiant look smaller than its carat weight suggests, because the extra weight sits below the table. Going shallow is not the safe alternative it sounds like: our reference radiant has a shallow pavilion of 30.3° and leaks 41.49% of the light entering it, against 1.88% for a round brilliant.
Both 1.00 to 1.05 for a square radiant and 1.15 to 1.35 for an elongated one are common, and neither is the standard. It is an outline preference. Our reference radiant sits at 1.28.
No. GIA issues cut grades for round brilliants only. That absence matters more on a radiant than on most shapes, because the cut is unusually sensitive to pavilion angle and there is no grade to catch a bad one.
Yes. The many small pavilion facets scatter light into a continuous glitter with no calm windows in it, so inclusions have plenty of visual noise to hide behind. A radiant is one of the more forgiving shapes on clarity.
Yes, and they are the most durable of the square and rectangular brilliants. The truncated corners remove the exposed points that make a princess vulnerable, so a radiant needs no special protective setting.
They share a family of outline and nothing else. Both are rectangular with cut corners. An emerald cut has step facets, flat planes in tiers, which produce broad slow flashes. A radiant has brilliant facets, which scatter light into fine continuous sparkle. They look entirely different in the hand.
Generally yes, per carat. A cut-cornered rectangle retains considerably more of the original rough than a round does, and that saving reaches the price.
Next
See the whole set on the jewellery cuts index, or the measured house and historic cuts in the cut registry.
Method
Monte-Carlo on exact facet geometry: 3,200 rays face-up plus 2,200 at 20° tilt, cosine-weighted from a 7° near-vertical cone. Useful light is what exits through the crown within 64° of vertical. The same protocol runs on every cut on this site, so the figures are comparable to each other.
They measure our reference geometry for the shape at the proportions listed above, not an average of stones on the market. A radiant cut to different proportions will read differently. Treat them as a like-for-like comparison between shapes, not as a grade for any individual stone.
Engine estimates, ±2 points, not lab-certified grades. We do not publish the Index symmetry axis on these pages: it scores facet regularity within each pavilion family, which is meaningful for a round brilliant and misleading for a shape whose pavilion is deliberately irregular.
73.64 here against the standard’s 71.82. The term is 100(1−e−n/45) on the count of facets that actually reach the surface, so it is a pure function of facet count and nothing else.