Portuguese Bird's Nest Cut Tourmaline: more facets, more sparkle
Brilliance 51 · Fire 12 · Scintillation 98 · in our census, where the T73 scores 86 · 50 · 80 in tourmaline
How the Portuguese Bird's Nest Cut handles light in tourmaline, measured: brilliance 51, fire 12 and 49% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Portuguese Bird's Nest Cut in tourmaline, face-up, from our own tracer at refractive index 1.603. Red, green and blue return light to the eye; gray leaks.
Portuguese Bird's Nest Cut Tourmaline
Tourmaline has a refractive index of 1.603 to 1.655 and a dispersion of 0.017. Its critical angle, from the low end of that range, is 38.6°, so a round design needs a pavilion of at least 38.6° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.629, the midpoint of the published range, and a fire spread of 0.015, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.603, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Portuguese Bird's Nest Cut in tourmaline live. Tourmaline is strongly doubly refractive (birefringence up to 0.040), so its back facets can look doubled. Our census traces one index (1.629), so the doubling is not in these figures.
The Portuguese Bird's Nest Cut has 177 facets, a table of 48.9% of its width and a total depth of 63.1% of its width; its pavilion mains sit at 38.0°. In tourmaline, the census returns 51 of 100 for brilliance and 12 for fire, against 86 and 50 for the T73, our benchmark, in the same stone; the same Portuguese Bird's Nest Cut in diamond reads 85 and 65.
Is tourmaline good in a Portuguese Bird's Nest? Pros and cons, measured
Compared with the T73 Round Brilliant in tourmaline and with the Portuguese Bird's Nest 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 Portuguese Bird's Nest Cut in tourmaline (white) against the T73 Round Brilliant in tourmaline (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 tourmaline: ahead on 2, level on 2, behind on 4.
Global60, the comparison 78, difference −18
Brilliance51, the comparison 86, difference −35
Fire12, the comparison 50, difference −38
Scintillation98, the comparison 80, difference +18
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm54, the comparison 93, difference −39
Tilt100, the comparison 74, difference +26
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; these are the same census figures as our Cut Performance Index.
What the Portuguese Bird's Nest Cut gains in tourmaline
More facets, more sparkle
Scintillation 98 against 80 for the T73 Round Brilliant in tourmaline: 18 points higher
Scintillation follows the number of facets the stone shows: 100 × (1 − e^(−facets / 45)). The Portuguese Bird's Nest Cut has 177 facets and the T73 73, so 98 against 80. It depends on the geometry alone, so it is the same in every stone.
Scintillation follows the number of facets: more facets, more and smaller flashes as the stone moves. Compare the facet counts under the drawings; each drawing shows only the crown. Drawn from each cut's own model.
0.99 ct at 6.5 mm, against 1.11 ct for the same cut in diamond (−11%)
Weight follows specific gravity: 3.13 for tourmaline against 3.52 for diamond, so the same model at the same size weighs 0.99 ct here and 1.11 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
A Portuguese Bird's Nest Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.
What the Portuguese Bird's Nest Cut gives up in tourmaline
Less fire in tourmaline than in diamond
Fire 12 against 65 for the Portuguese Bird's Nest Cut in diamond: 53 points lower
Fire is the share of the returned light that splits into color at the exit facet: the census traces each exit again at the refractive index minus and plus the fire spread (0.015 in tourmaline) and counts a ray as fire when the two directions differ by more than 0.6°. The Portuguese Bird's Nest Cut reads 12 against 65 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders tourmaline's fire live.
The fire figure is the census's, traced at the refractive index minus and plus the fire spread. See the fire in the 3D Gemstone Simulator: the Portuguese Bird's Nest Cut in tourmaline under the sunny-day lighting.
What helps:the Oval Cut reads 80 for fire in tourmaline, the best of the cuts we score there.
Leakage 49 against 13 for the Portuguese Bird's Nest Cut in diamond: 36 points higher
Leakage is the share of the census rays that enter the stone and leave through the pavilion, or through the crown heading down. The Portuguese Bird's Nest Cut leaks 49% in tourmaline against 13% for the same cut in diamond. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Portuguese Bird's Nest Cut in tourmaline · Leakage 49
0° · 66% leak
10° · 52% leak
20° · 41% leak
30° · 40% leak
Portuguese Bird's Nest Cut in diamond · Leakage 13
0° · 13% leak
10° · 8% leak
20° · 8% leak
30° · 8% leak
Each frame is the Light Return map with the stone tilted away from you by the angle shown; gray is leakage. The share under each frame is that picture's own.
What helps:the DG-M5 reads 4% for leakage in tourmaline, the best of the cuts we score there.
Brilliance 51 against 86 for the T73 Round Brilliant in tourmaline: 35 points lower
Brilliance is the share of the 3,200 census rays that enter the stone and come back out of the crown towards the viewer. In tourmaline, whose critical angle is 38.6°, the Portuguese Bird's Nest Cut returns 51 of 100 and the T73 86. The Portuguese Bird's Nest Cut's pavilion mains sit at 38.0°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Portuguese Bird's Nest Cut in tourmaline · Brilliance 51
T73 Round Brilliant in tourmaline · Brilliance 86
Red, green and blue = light returning to the eye; gray = leakage, light that leaves heading down or stays inside. 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:the DG-M5 reads 96 for brilliance in tourmaline, the best of the cuts we score there.
Our verdict on the Portuguese Bird's Nest Cut in tourmaline
Pick the Portuguese Bird's Nest Cut in tourmaline for this: it has more facets to sparkle with and weighs less than in diamond. The catch: it shows less fire than in diamond, leaks more than in diamond and returns less light than the T73.
If that catch matters more to you, the Oval Cut reads 80 for fire in tourmaline, the best of the cuts we score there.
Every figure on this page is from our light census, traced at one refractive index: a simulation of the geometry, not a grading report. The 3D files and cutting files below are the same Portuguese Bird's Nest Cut model we traced.
Portuguese Bird's Nest Cut Tourmaline: questions
Is the Portuguese Bird's Nest a good cut for tourmaline?
In our census the Portuguese Bird's Nest Cut returns 51 of 100 for brilliance and 12 for fire in tourmaline, against 86 and 50 for the T73 in the same stone. Against that round and against the same cut in diamond it has 2 pros and 3 cons by our thresholds; the summary above names them.
What pavilion angle does tourmaline need?
At least 38.6° for a round design: tourmaline's critical angle is 38.6°, from the low end of its refractive index range, and head-on light has to reflect off both sides of the pavilion and leave through the table. The Portuguese Bird's Nest Cut's pavilion mains sit at 38.0°.
How much does a Portuguese Bird's Nest weigh in tourmaline?
At 6.5 mm across, 0.99 ct in tourmaline, against 1.11 ct for the same cut in diamond (-11%): tourmaline's specific gravity is 3.13, diamond's 3.52.
Can I see the Portuguese Bird's Nest in tourmaline in 3D?
Yes: the 3D Gemstone Simulator renders it live, with tourmaline's own refractive index and dispersion. Tourmaline is traced by the same light census as the other gemstones, with its refractive index and fire spread derived from published values, so its scores are on the same scale; the pictures here are our Light Return tracer, and the Cut Performance Wheel sets it against any other cut and stone.
Get the Portuguese Bird's Nest Cut files
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Portuguese Bird's Nest Cut 3D files
The Portuguese Bird's Nest Cut as exact geometry: 177 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
