---
title: "Portuguese Bird's Nest Cut Iolite: Pros, Cons and Scores"
description: "Portuguese Bird's Nest Cut in iolite: brilliance 37, fire 10, leakage 63%, 2 pros and 3 cons against the T73, from our ray-traced light census."
url: https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest
image: https://digitalgemology.com/img/stone-cuts/portuguese-birds-nest-iolite-og.jpg?v=f2936744
---

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# Portuguese Bird's Nest Cut Iolite: lighter than the same cut in diamond

**Buy (instant download, personal-use license):** [Portuguese Bird's Nest Cut 3D files, €9.99 · Personal use](https://digitalgemology.lemonsqueezy.com/checkout/buy/260cf8a0-6a47-4ff7-91e0-e41657dd7730) · [Portuguese Bird's Nest Cut cutting files, €6.99 · Personal use](https://digitalgemology.lemonsqueezy.com/checkout/buy/57a8bbc7-5d29-4910-9a85-9c0656d946a0) · [Get the cube free](https://digitalgemology.lemonsqueezy.com/checkout/buy/2d1ab55f-2bd6-4897-a4cd-f3320f54e99e)

Brilliance 37 · Fire 10 · Scintillation 98 · in our census, where the T73 scores 72 · 58 · 80 in iolite

How the Portuguese Bird's Nest Cut handles light in iolite, measured: brilliance 37, fire 10 and 63% leakage, set against the T73 in the same stone and against the same cut in diamond.

[Get the files](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest#buy) [Open it in the Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=portuguese-birds-nest&stone=iolite&ct=1.00&view=angle&lighting=studio&turn=0) [All cuts in iolite](https://digitalgemology.com/gemstones/iolite)

Light Return map of the Portuguese Bird's Nest Cut in iolite, face-up, from our own tracer at refractive index 1.542. Red, green and blue return light to the eye; gray leaks.

## Portuguese Bird's Nest Cut Iolite

Iolite has a refractive index of 1.542 to 1.551 and a dispersion of 0.017. Its critical angle, from the low end of that range, is 40.4°, so a round design needs a pavilion of at least 40.4° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.547, 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 1.542, 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 iolite live.

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 iolite, the census returns 37 of 100 for brilliance and 10 for fire, against 72 and 58 for the T73, our benchmark, in the same stone; the same Portuguese Bird's Nest Cut in diamond reads 85 and 65.

## Is iolite good in a Portuguese Bird's Nest? Pros and cons, measured

### Pros

- [Lighter than the same cut in diamond](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest#pro-weight) 0.83 vs 1.11 ct
- [More facets, more sparkle](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest#pro-scint) 98 vs 80

### Cons

- [Less fire in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest#con-fire) 10 vs 65
- [Leaks more in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest#con-leak) 63 vs 13
- [Dimmer in iolite than in diamond](https://digitalgemology.com/gemstones/iolite/portuguese-birds-nest#con-brilliance) 37 vs 85

Compared with the T73 Round Brilliant in iolite 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](https://digitalgemology.com/about/how-we-measure).

## All eight scores against the T73

At a glance: the Portuguese Bird's Nest Cut in iolite (white) against the T73 Round Brilliant in iolite (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 iolite: ahead on 2, level on 2, behind on 4.

- Global 54, the comparison 74, difference −20
- Brilliance 37, the comparison 72, difference −35
- Fire 10, the comparison 58, difference −48
- Scintillation 98, the comparison 80, difference +18
- Spread 100, the comparison 100, difference 0
- Symmetry 100, the comparison 100, difference 0
- Shape-norm 39, the comparison 77, difference −38
- Tilt 100, the comparison 81, difference +19

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](https://digitalgemology.com/tools/cut-performance-wheel?cut=portuguese-birds-nest&stone=iolite); these are the same census figures as our [Cut Performance Index](https://digitalgemology.com/learn/cut-performance-index).

## What the Portuguese Bird's Nest Cut gains in iolite

### Lighter than the same cut in diamond

**0.83 ct** at 6.5 mm, against 1.11 ct for the same cut in diamond (−26%)

Weight follows specific gravity: 2.61 for iolite against 3.52 for diamond, so the same model at the same size weighs 0.83 ct here and 1.11 ct in diamond, 6.5 mm across. Nothing about the light changes with it.

*Weight of a 6.5 mm Portuguese Bird's Nest Cut: 0.83 ct in iolite, 1.11 ct in diamond*

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

[Try it yourself: Weights in every gemstone on the Portuguese Bird's Nest Cut page](https://digitalgemology.com/cuts/portuguese-birds-nest#stones)

### More facets, more sparkle

**Scintillation 98** against 80 for the T73 Round Brilliant in iolite: 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.

*Facet diagram of the Portuguese Bird's Nest Cut: its crown, seen face-up, 177 facets in all*

Portuguese Bird's Nest Cut · 177 facets · Scintillation 98

*Facet diagram of the T73 Round Brilliant: its crown, seen face-up, 73 facets in all*

T73 Round Brilliant · 73 facets · Scintillation 80

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.

[Try it yourself: Compare the Scintillation spoke in the Cut Performance Wheel](https://digitalgemology.com/tools/cut-performance-wheel?cut=portuguese-birds-nest&stone=iolite)

## What the Portuguese Bird's Nest Cut gives up in iolite

### Less fire in iolite than in diamond

**Fire 10** against 65 for the Portuguese Bird's Nest Cut in diamond: 55 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 iolite) and counts a ray as fire when the two directions differ by more than 0.6°. The Portuguese Bird's Nest Cut reads 10 against 65 for the same cut in diamond. The figure is the census's; the 3D Gemstone Simulator renders iolite'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](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=portuguese-birds-nest&stone=iolite&ct=1.00&view=up&lighting=sun&turn=0): the Portuguese Bird's Nest Cut in iolite under the sunny-day lighting.

**What helps:** [the Oval Cut](https://digitalgemology.com/gemstones/iolite/oval) reads 82 for fire in iolite, the best of the cuts we score there.

[Try it yourself: See the fire in the 3D Gemstone Simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=portuguese-birds-nest&stone=iolite&ct=1.00&view=up&lighting=sun&turn=0)

### Leaks more in iolite than in diamond

**Leakage 63** against 13 for the Portuguese Bird's Nest Cut in diamond: 50 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 63% in iolite 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 iolite · Leakage 63

0° · 68% leak

10° · 58% leak

20° · 53% leak

30° · 48% 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](https://digitalgemology.com/gemstones/iolite/dg-m5) reads 15% for leakage in iolite, the best of the cuts we score there.

[Try it yourself: Tilt it yourself in the simulator's light map](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=portuguese-birds-nest&stone=iolite&ct=1.00&view=up&map=1&turn=0)

### Dimmer in iolite than in diamond

**Brilliance 37** against 85 for the Portuguese Bird's Nest Cut in diamond: 48 points lower

The same cut in diamond returns 85. Iolite bends light less than diamond: its critical angle is 40.4°, diamond's 24.4°, so a pavilion facet has to be steeper before light reflects off it rather than passing out. The Portuguese Bird's Nest Cut's pavilion returns less of iolite's light than of diamond's, as the two maps show.

Portuguese Bird's Nest Cut in iolite · Brilliance 37

Portuguese Bird's Nest Cut in diamond · Brilliance 85

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](https://digitalgemology.com/gemstones/iolite/dg-m5) reads 85 for brilliance in iolite, the best of the cuts we score there.

[Try it yourself: Open this Light Return map in the simulator](https://digitalgemology.com/tools/3d_gemstone_simulator?cut=portuguese-birds-nest&stone=iolite&ct=1.00&view=up&map=1&turn=0)

## Our verdict on the Portuguese Bird's Nest Cut in iolite

Pick the Portuguese Bird's Nest Cut in iolite for this: it weighs less than in diamond and has more facets to sparkle with. The catch: it shows less fire than in diamond, leaks more than in diamond and returns less light than in diamond.

If that catch matters more to you, [the Oval Cut](https://digitalgemology.com/gemstones/iolite/oval) reads 82 for fire in iolite, 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 Iolite: questions

### Is the Portuguese Bird's Nest a good cut for iolite?

In our census the Portuguese Bird's Nest Cut returns 37 of 100 for brilliance and 10 for fire in iolite, against 72 and 58 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 iolite need?

At least 40.4° for a round design: iolite's critical angle is 40.4°, 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 iolite?

At 6.5 mm across, 0.83 ct in iolite, against 1.11 ct for the same cut in diamond (-26%): iolite's specific gravity is 2.61, diamond's 3.52.

### Can I see the Portuguese Bird's Nest in iolite in 3D?

Yes: the 3D Gemstone Simulator renders it live, with iolite's own refractive index and dispersion. Iolite 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

*6 formats* *Millimeters* *Watertight*

### 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.

- **STEP** Exact faceted solid for CAD
- **3DM** Rhino, closed mesh on its own layer
- **STL** Watertight mesh for printing and casting
- **OBJ** Mesh for modeling and rendering
- **FBX** Blender, 3ds Max, Maya, Cinema 4D, Unity, Unreal
- **GLB** Web, AR and quick previews

€9.99 · [Personal use](https://digitalgemology.com/licence) [Buy the 3D files](https://digitalgemology.lemonsqueezy.com/checkout/buy/260cf8a0-6a47-4ff7-91e0-e41657dd7730)

*GemCad* *96 index*

### Portuguese Bird's Nest Cut cutting files

The Portuguese Bird's Nest Cut as a faceting design: 161 + 16 girdles = 177 facets, 96 index, 16-fold mirror-image symmetry, ready for the machine.

- **.asc** GemCad design file, 96 index gear
- **.csv** Tier table: angles, indices and cutting order
- **Diagram** Printable faceting diagram

€6.99 · [Personal use](https://digitalgemology.com/licence) [Buy the cutting files](https://digitalgemology.lemonsqueezy.com/checkout/buy/57a8bbc7-5d29-4910-9a85-9c0656d946a0)

Not sure the files open in your software? [Get the cube free](https://digitalgemology.lemonsqueezy.com/checkout/buy/2d1ab55f-2bd6-4897-a4cd-f3320f54e99e): the same six formats, for your email address, used only to send them ([privacy](https://digitalgemology.com/privacy#free-sample)).

Questions before you buy? [Email us](mailto:support@digitalgemology.com).

## More gemstones and cuts

[Iolite: optical properties and the top ten cuts](https://digitalgemology.com/gemstones/iolite) · [The Portuguese Bird's Nest Cut: specifications, model and files](https://digitalgemology.com/cuts/portuguese-birds-nest)

### Other cuts in iolite

- [T73 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t73-round-brilliant)
- [T105 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t105-round-brilliant)
- [DG-Vitruvio](https://digitalgemology.com/gemstones/iolite/dg-vitruvio)
- [DG-Anteros](https://digitalgemology.com/gemstones/iolite/dg-anteros)
- [DG-Broken Hearts and Arrows](https://digitalgemology.com/gemstones/iolite/dg-broken-hearts-and-arrows)
- [Baguette Cut](https://digitalgemology.com/gemstones/iolite/baguette)
- [Emerald Cut](https://digitalgemology.com/gemstones/iolite/emerald-cut)
- [Marquise Cut](https://digitalgemology.com/gemstones/iolite/marquise)
- [Oval Cut](https://digitalgemology.com/gemstones/iolite/oval)
- [Pear Cut](https://digitalgemology.com/gemstones/iolite/pear)
- [Radiant Cut](https://digitalgemology.com/gemstones/iolite/radiant)
- [Rectangle Cut](https://digitalgemology.com/gemstones/iolite/rectangle)
- [Teardrop Cut](https://digitalgemology.com/gemstones/iolite/teardrop)
- [Asscher Cut](https://digitalgemology.com/gemstones/iolite/asscher)
- [Cushion Cut](https://digitalgemology.com/gemstones/iolite/cushion)
- [Emerald Square Cut](https://digitalgemology.com/gemstones/iolite/emerald-square)
- [Princess Cut](https://digitalgemology.com/gemstones/iolite/princess)
- [Radiant Square Cut](https://digitalgemology.com/gemstones/iolite/radiant-square)
- [Square Cut](https://digitalgemology.com/gemstones/iolite/square)
- [Triangle Cut](https://digitalgemology.com/gemstones/iolite/triangle)
- [Trilliant Cut](https://digitalgemology.com/gemstones/iolite/trilliant)
- [Trillion Cut](https://digitalgemology.com/gemstones/iolite/trillion)
- [Hexagon Cut](https://digitalgemology.com/gemstones/iolite/hexagon)
- [Octagon Cut](https://digitalgemology.com/gemstones/iolite/octagon)
- [Old Single Cut](https://digitalgemology.com/gemstones/iolite/old-single)
- [Mazarin Cut](https://digitalgemology.com/gemstones/iolite/mazarin)
- [Peruzzi Cut](https://digitalgemology.com/gemstones/iolite/peruzzi)
- [Old Mine Cut](https://digitalgemology.com/gemstones/iolite/old-mine)
- [Old European Cut](https://digitalgemology.com/gemstones/iolite/old-european)
- [T57 Round Brilliant](https://digitalgemology.com/gemstones/iolite/t57-round-brilliant)
- [DG-M5](https://digitalgemology.com/gemstones/iolite/dg-m5)
- [DG-Miliano](https://digitalgemology.com/gemstones/iolite/dg-miliano)
- [DG-Rafaello](https://digitalgemology.com/gemstones/iolite/dg-rafaello)
- [DG-Bowtie](https://digitalgemology.com/gemstones/iolite/dg-bowtie)
- [DG-Elongated Hexagon](https://digitalgemology.com/gemstones/iolite/dg-elongated-hexagon)
- [DG-Octagonal Kite](https://digitalgemology.com/gemstones/iolite/dg-octagonal-kite)

### The Portuguese Bird's Nest Cut in other gemstones

- [Diamond](https://digitalgemology.com/gemstones/diamond/portuguese-birds-nest)
- [Moissanite](https://digitalgemology.com/gemstones/moissanite/portuguese-birds-nest)
- [Cubic Zirconia](https://digitalgemology.com/gemstones/cubic-zirconia/portuguese-birds-nest)
- [Ruby](https://digitalgemology.com/gemstones/ruby/portuguese-birds-nest)
- [Sapphire](https://digitalgemology.com/gemstones/sapphire/portuguese-birds-nest)
- [Emerald](https://digitalgemology.com/gemstones/emerald/portuguese-birds-nest)
- [Amethyst](https://digitalgemology.com/gemstones/amethyst/portuguese-birds-nest)
- [Topaz](https://digitalgemology.com/gemstones/topaz/portuguese-birds-nest)
- [Spinel](https://digitalgemology.com/gemstones/spinel/portuguese-birds-nest)
- [Demantoid](https://digitalgemology.com/gemstones/demantoid/portuguese-birds-nest)
- [Zircon](https://digitalgemology.com/gemstones/zircon/portuguese-birds-nest)
- [Tourmaline](https://digitalgemology.com/gemstones/tourmaline/portuguese-birds-nest)
- [Peridot](https://digitalgemology.com/gemstones/peridot/portuguese-birds-nest)
- [Tanzanite](https://digitalgemology.com/gemstones/tanzanite/portuguese-birds-nest)
- [YAG](https://digitalgemology.com/gemstones/yag/portuguese-birds-nest)
- [Pyrope](https://digitalgemology.com/gemstones/pyrope/portuguese-birds-nest)
- [Almandine](https://digitalgemology.com/gemstones/almandine/portuguese-birds-nest)
- [Spessartine](https://digitalgemology.com/gemstones/spessartine/portuguese-birds-nest)
- [Grossular](https://digitalgemology.com/gemstones/grossular/portuguese-birds-nest)
- [Chrysoberyl](https://digitalgemology.com/gemstones/chrysoberyl/portuguese-birds-nest)
- [Kunzite](https://digitalgemology.com/gemstones/kunzite/portuguese-birds-nest)
- [Morganite](https://digitalgemology.com/gemstones/morganite/portuguese-birds-nest)
- [GGG](https://digitalgemology.com/gemstones/ggg/portuguese-birds-nest)
- [Strontium titanate](https://digitalgemology.com/gemstones/strontium-titanate/portuguese-birds-nest)
- [Synthetic rutile](https://digitalgemology.com/gemstones/synthetic-rutile/portuguese-birds-nest)