Portuguese Bird's Nest Cut Diamond: as much scintillation as any cut we measure
Brilliance 85 · Fire 65 · Scintillation 98 · in our census, where the T73 scores 93 · 78 · 80 in diamond
A woven nest of facets that sparkles as finely as anything we measure, and pays for it in diamond with less light, less fire and more leakage than the T73.
Rendered in our 3D Gemstone Simulator from the Portuguese Bird's Nest Cut model, 1.00 ct, studio light.
Portuguese Bird's Nest Cut Diamond
Sixteen-fold and built in tiers, five above the girdle and five below, the Portuguese cut offsets each tier half an index step from its neighbour, so the facets lock together like a woven nest. The model we measured has 177 facets, a 48.9% table, a low 26.0° crown and a 38.0° pavilion, 63.1% deep overall.
It is a long-standing favourite for coloured stones and a showpiece for the faceting machine. In diamond, against the T73 Round Brilliant, it wins one score clearly and loses three.
Is a Portuguese cut good for diamond? Pros and cons
Compared with the T73 Round Brilliant in diamond.
A difference counts from 3 points (Brilliance, Fire, Tilt, Leakage), 5 (Scintillation,
Symmetry), 2 (Spread) 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 diamond (white) against the T73 Round Brilliant in diamond (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 diamond: ahead on 2, level on 2, behind on 4.
Global86, the comparison 90, difference −4
Brilliance85, the comparison 93, difference −8
Fire65, the comparison 78, difference −13
Scintillation98, the comparison 80, difference +18
Spread100, the comparison 100, difference 0
Symmetry100, the comparison 100, difference 0
Shape-norm91, the comparison 100, difference −9
Tilt100, the comparison 92, difference +8
Face-up light census, a different measure from the Cut Grading Tool; Spread and Shape-norm above 100 sit on the ring.
Scintillation 98 against 80 for the T73 Round Brilliant in diamond: 18 points higher
Five tiers above and five below, each offset from the next, give 177 facets against the T73's 73. Our scintillation score rises with that count and tops out here; no cut we measure in diamond scores higher.
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.
Fire 65 against 78 for the T73 Round Brilliant in diamond: 13 points lower
Fire is the largest of its three cons. With so many small facets, the light that returns comes back in many small pieces, and less of it is spread into colour.
Portuguese Bird's Nest Cut in diamond · Fire 65
T73 Round Brilliant in diamond · Fire 78
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.
What helps: For a fine-sparkling round with more fire, DG-Miliano Diamond scores 82 with the same top-of-scale scintillation.
Leakage 13 against 2 for the T73 Round Brilliant in diamond: 11 points higher
In our census 13% of the light escapes through the pavilion, against 2% for the T73. DG-Miliano carries the same number of facets and leaks far less, so the facet count alone does not explain it.
Portuguese Bird's Nest Cut in diamond · Leakage 13
0° · 12% leak
10° · 8% leak
20° · 8% leak
30° · 8% leak
T73 Round Brilliant in diamond · Leakage 2
0° · 4% leak
10° · 2% leak
20° · 9% leak
30° · 14% leak
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: Our data does not point to a pavilion fix: its 38.0° figure sits just under the 38.9° guide minimum for round designs, but we have not measured a steeper version. DG-Miliano Diamond leaks 3% with as many facets.
Brilliance 85 against 93 for the T73 Round Brilliant in diamond: 8 points lower
Brilliance trails the T73 by a clear margin. Much of the gap is the light counted as leakage: light that leaves through the back cannot come up to the eye.
Portuguese Bird's Nest Cut in diamond · Brilliance 85
T73 Round Brilliant in diamond · Brilliance 93
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:DG-Vitruvio Diamond matches its scintillation at 98 and returns 93 brilliance.
Choose the Portuguese cut in diamond for the facet pattern itself: a showpiece of sixteen-fold symmetry whose sparkle tops our scale. Expect a stone with less light and much less colour than a modern round.
For sparkle, yes: Scintillation 98 against 80 for the T73. For light and fire, no: Brilliance 85 and Fire 65, against 93 and 78.
Does a Portuguese cut diamond hold its light when tilted?
Its Tilt score is 100, the top of the scale, but Tilt is the share of its own light a stone keeps, and at 85 brilliance that is a share of a smaller amount. We do not count it as a pro.
How many facets does a Portuguese Bird's Nest cut have?
Our model has 177, in five crown tiers and five pavilion tiers on a sixteen-fold plan.
What does a 6.5 mm Portuguese cut diamond weigh?
1.11 ct: at 63.1% deep it is heavier for its width than the T73.
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.
