Radiant Cut Sapphire: Pros, Cons & Light Leakage

The radiant puts a brilliant facet plan under the outline of a step cut, cropped corners and all. Our model is 1.284 to 1 and 53.8% deep, with 74 facets.

Sapphire gains two things in this cut, fire and face-up size, both against the T73. It also has the second-lowest brilliance in our sapphire census, after DG-Bowtie, and the highest leakage of any cut we measure in sapphire.

Is sapphire good in a radiant cut? Pros and cons

Pros

Nearly twice the T73's fire 69 vs 37
Faces up larger for its weight 118 vs 100

Cons

Under a third of the T73's light 26 vs 94
Two-thirds of the light leaks 67 vs 5
Heavier than a diamond radiant of the same width 1.78 vs 1.56 ct
A little less sparkle than the round 74 vs 80

Compared with the T73 Round Brilliant in sapphire and with the Radiant Cut in diamond. A difference counts from 3 points (Brilliance, Fire, Tilt, Leakage), 5 (Scintillation, Symmetry), 4% (face-up size per carat) or 5% (weight); Tilt counts as a pro only for a stone within 5 points of the brilliance it is compared with. How we measure.

All eight scores against the T73

At a glance: the Radiant Cut in sapphire (white) against the T73 Round Brilliant in sapphire (dashed): solid white where it reaches further, hatched where it falls short. Each pro and con is explained, with pictures, below.

Against the T73 Round Brilliant in sapphire: ahead on 3, behind on 5.

Global59, the comparison 79, difference −20
Brilliance26, the comparison 94, difference −68
Fire69, the comparison 37, difference +32
Scintillation74, the comparison 80, difference −6
Spread105, the comparison 100, difference +5
Symmetry99, the comparison 100, difference −1
Shape-norm31, the comparison 102, difference −71
Tilt100, the comparison 75, difference +25

Face-up light census, a different measure from the Cut Grading Tool; Spread and Shape-norm above 100 sit on the ring. Spread is the census's estimate from depth alone; the face-up size in the pros and cons is measured from each model's outline.

Open it in the Cut Performance Wheel

What a sapphire gains as a radiant

Nearly twice the T73's fire

Fire 69 against 37 for the T73 Round Brilliant in sapphire: 32 points higher

Fire 69 against 37, the third-highest score we measure in sapphire, after the oval and DG-Elongated Hexagon. Read it beside the brilliance: the colour comes from a stone that returns little light overall, 26.

Radiant cut in sapphire face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 69) — Look at the coloured flashes: those are fire. Same light, same size, same face-up angle; rendered by our 3D Gemstone Simulator from each cut's own model.

T73 round brilliant in sapphire face-up under a single bright light: a render from our simulator, its coloured flashes are the fire (score 37) — Look at the coloured flashes: those are fire. Same light, same size, same face-up angle; rendered by our 3D Gemstone Simulator from each cut's own model.

Try it yourself: See the fire in the 3D Gemstone Simulator

Faces up larger for its weight

Face-up size 118 against 100 for the T73 Round Brilliant in sapphire (T73 = 100): 18% more face-up area for the same weight

Measured from each model's outline, it carries less weight under each square millimetre of its face than the T73. Only the marquise and the rectangle face up larger for their weight among the cuts we measure.

Radiant Cut · 6.63 x 3.61 mm at 1.00 ct · Face-up size 118

T73 Round Brilliant · 6.21 mm at 1.00 ct · Face-up size 100

Both stones weigh 1.00 ct in sapphire and are drawn to the same scale in millimetres, from each cut's own model. Face-up size is the outline's area per carat, with the T73 at 100: a deeper stone, or a rounder outline, spreads less area for its weight.

Try it yourself: See its size at 1.00 ct in sapphire in the 3D Gemstone Simulator

Where the radiant costs a sapphire

Under a third of the T73's light

Brilliance 26 against 94 for the T73 Round Brilliant in sapphire: 68 points lower

Brilliance 26 against 94. The same radiant in diamond returns 32, so the design is dim in both stones; sapphire's lower refractive index, 1.762–1.770 against diamond's 2.417, takes a little more.

Radiant cut in sapphire face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 26) — Red, green and blue = light returning to the eye; grey = light leaving through the pavilion. This is the head-on view; the Brilliance score averages a wider cone of light, so the score can differ from what one picture shows.

T73 round brilliant in sapphire face-up Light Return map: red, green and blue show where the light returns from, grey shows where it leaks (Brilliance 94) — Red, green and blue = light returning to the eye; grey = light leaving through the pavilion. This is the head-on view; the Brilliance score averages a wider cone of light, so the score can differ from what one picture shows.

What helps: For a cornered outline with far more light, the Cushion Cut Sapphire returns 88; the Radiant Square Cut Sapphire, the same idea on a square, returns 76.

Try it yourself: Open this Light Return map in the simulator

Two-thirds of the light leaks

Leakage 67 against 5 for the T73 Round Brilliant in sapphire: 62 points higher

67% of the light in our census leaves through the pavilion, where the T73 loses 5%. The diamond radiant loses 41%, so the stone adds a good deal to what the design already lets out.

Radiant cut in sapphire tilted 0 degrees: Light Return map, 70% of the face leaking — Each frame is the Light Return map with the stone tilted away from you by the angle shown; grey is light leaving through the pavilion. The share under each frame is that picture's own.

Radiant cut in sapphire tilted 10 degrees: Light Return map, 63% of the face leaking — Each frame is the Light Return map with the stone tilted away from you by the angle shown; grey is light leaving through the pavilion. The share under each frame is that picture's own.

What helps: Size changes nothing here: the same angles leak the same share in a smaller stone. The Cushion Cut Sapphire leaks 11%, DG-M5 Sapphire 0%.

Try it yourself: Tilt it yourself in the simulator's light map

Heavier than a diamond radiant of the same width

1.78 ct at 6.5 mm, against 1.56 ct for the same cut in diamond (+14%)

At 6.5 mm wide, our radiant weighs 1.78 ct in sapphire and 1.56 ct in diamond: sapphire's specific gravity is 4.00, diamond's 3.52.

A Radiant Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.

What helps: Order it by length and width, not carats.

Try it yourself: Weights in all seven gemstones on the Radiant Cut page

A little less sparkle than the round

Scintillation 74 against 80 for the T73 Round Brilliant in sapphire: 6 points lower

Scintillation 74 against 80. It carries 74 facets to the T73's 73, laid out on a rectangle; the gap is a few points.

Radiant Cut · 74 facets · Scintillation 74

T73 Round Brilliant · 73 facets · Scintillation 80

Scintillation follows the number of facets: more facets, more and smaller flashes as the stone moves. Count the facets in each crown. Drawn from each cut's own model.

What helps: For more sparkle with corners, the Cushion Cut Sapphire scores 85.

Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel

Who a radiant sapphire suits

The radiant suits a sapphire chosen for flashes of colour and a large face for its weight, in a design where light return is not the point. In our census it is the weakest sapphire cut at keeping light inside the stone.

For a cornered sapphire with light, the Cushion Cut Sapphire. For the most light of all, DG-M5 Sapphire. In diamond the radiant gains fire, 77, and a little light, 32.

Radiant Cut Sapphire: questions

Is a radiant cut good for sapphire?

For fire and size, yes: Fire 69 against 37 and Face-up size 118. For light, no: Brilliance 26, with 67% leaking.

Why does a radiant sapphire look dark?

Two-thirds of its light, 67% in our census, escapes through the pavilion; a T73 Round Brilliant in sapphire loses 5%.

Radiant or cushion for a sapphire?

The cushion returns far more light (88 against 26) and leaks less (11% against 67%); the radiant has more fire, 69 against 36, and faces up larger.

What does a 6.5 mm wide radiant sapphire weigh?

About 1.78 ct; a diamond radiant of the same width is 1.56 ct.

Get the Radiant Cut files

6 formatsMillimetresWatertight

Radiant Cut 3D files

The Radiant Cut as exact geometry: 74 planar facets, real-world scale, ready for CAD, rendering, printing and casting.

STEPExact faceted solid for CAD
3DMRhino, closed mesh on its own layer
STLWatertight mesh for printing and casting
OBJMesh for modelling and rendering
FBXBlender, 3ds Max, Maya, Cinema 4D, Unity, Unreal
GLBWeb, AR and quick previews

€9.99 · Personal useBuy the 3D files

In preparation

Radiant Cut cutting files

The faceting design for the Radiant Cut is in preparation. It will include the GemCad file, the tier table and a printable diagram.

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More gemstones and cuts

Sapphire: optical properties and the top ten cuts · The Radiant Cut: specifications, model and files

Radiant Cut Sapphire: almost twice the round's fire, and a larger face for its weight