3D model and faceting diagram · 177 facets · 7.90 x 7.90 mm
The traditional Portuguese cut: sixteen-fold, with five crown tiers and five pavilion tiers. Each tier is offset half an index step from the tier above, so the facets interlock into a woven 'bird's nest'.
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The traditional Portuguese cut: sixteen-fold, with five crown tiers and five pavilion tiers. Each tier is offset half an index step from the tier above, so the facets interlock into a woven 'bird's nest'.
It has well over a hundred facets. It is a showpiece for the faceting machine and a long-standing favorite for colored stones.
Measured from the delivered model, not quoted from a standard.
The Portuguese Bird's Nest Cut performs best in moissanite, where its brilliance and fire together are highest: 82 for brilliance and 95 for fire. In diamond it scores 85 for brilliance and 65 for fire, against 93 and 78 for the T73 benchmark. Its scintillation, 98, comes from its pattern of facets, so it is the same in every stone.
| Gemstone | Brilliance | Fire | Scintillation |
|---|---|---|---|
| Diamond | 85 (T73 benchmark 93) | 65 (T73 benchmark 78) | 98 (T73 benchmark 80) |
| Moissanite | 82 (T73 benchmark 86) | 95 (T73 benchmark 97) | 98 (T73 benchmark 80) |
| Cubic Zirconia | 83 (T73 benchmark 98) | 79 (T73 benchmark 87) | 98 (T73 benchmark 80) |
| Ruby | 69 (T73 benchmark 94) | 16 (T73 benchmark 37) | 98 (T73 benchmark 80) |
| Sapphire | 69 (T73 benchmark 94) | 16 (T73 benchmark 37) | 98 (T73 benchmark 80) |
| Emerald | 42 (T73 benchmark 78) | 2 (T73 benchmark 39) | 98 (T73 benchmark 80) |
| Amethyst | 37 (T73 benchmark 72) | 1 (T73 benchmark 36) | 98 (T73 benchmark 80) |
Brilliance is the share of face-up light that the stone returns. Fire is the share of that light that splits into color. Both come from our face-up light census. Scintillation is the sparkle that the facets give as the stone moves, and we read it from its facets. They are the same figures as the Cut Performance Wheel, where you can compare the Portuguese Bird's Nest Cut with any other cut. A simulation of the geometry, not a grading report.
The same geometry behaves differently in every material. Light that meets a pavilion facet at less than the critical angle of the stone does not reflect. It passes straight out of the back and shows face-up as a window. For each stone, we measured how much of the pavilion of this model, seen face-down, is steeper than that angle. We also measured what the model weighs at its reference size. The pavilion mains of this design sit at 38.0°. A round design needs at least 40.4° in amethyst for head-on light to reflect off both sides of the pavilion and leave through the table. So it is worth making the mains steeper for emerald, amethyst.
| Stone | Refractive index | Critical angle | Pavilion reflecting head-on light | Weight at this size | Verdict |
|---|---|---|---|---|---|
| Diamond | 2.417 | 24.4° | 100% | 2.00 ct | Holds head-on light |
| Moissanite | 2.648 to 2.691 | 22.2° | 100% | 1.83 ct | Holds head-on light |
| Cubic Zirconia | 2.15 to 2.18 | 27.7° | 100% | 3.30 ct | Holds head-on light |
| Ruby | 1.762 to 1.770 | 34.6° | 100% | 2.27 ct | Holds head-on light |
| Sapphire | 1.762 to 1.770 | 34.6° | 100% | 2.27 ct | Holds head-on light |
| Emerald | 1.577 to 1.583 | 39.4° | 78% | 1.55 ct | Steepen the pavilion |
| Amethyst | 1.544 to 1.553 | 40.4° | 78% | 1.51 ct | Steepen the pavilion |
Head-on light, first reflection. The 3D Gemstone Simulator traces the full Light Return in each of these gemstones.
The Portuguese Bird's Nest Cut stone by stone: what each gemstone gains and loses in this cut, measured.
Open it in the 3D Gemstone Simulator. Set its carat, color, clarity and cut grade in any of seven gemstones. Turn it under ten kinds of light, and watch its 3D gemstone report change as you go. Free, in your browser.
Six formats. STEP is the exact faceted solid for CAD, and 3DM is for Rhino. STL and OBJ are meshes. FBX is for Blender, 3ds Max, Maya, Cinema 4D, Unity and Unreal. GLB is for the web and AR. All are in millimeters at real-world scale, with 177 planar facets.
Yes. The cutting files contain a GemCad .asc design (161 + 16 girdles = 177 facets, 96 index, 16-fold mirror-image symmetry) and a printable faceting diagram. They also contain a tier table in CSV, with the angles, indices and cutting order.
We measured the pavilion of this model against the critical angle of each stone. In Diamond, Moissanite, Cubic Zirconia, Ruby, Sapphire, the whole pavilion reflects head-on light. In Emerald, Amethyst, part of the pavilion lets light out of the back, so we advise a steeper pavilion. The pavilion mains of this design sit at 38.0°. A round design needs at least 40.4° in amethyst for head-on light to reflect off both sides of the pavilion and leave through the table. So it is worth making the mains steeper for emerald, amethyst.
We check it facet by facet against the 3D model that it was written from. Every crown and pavilion facet within 0.001° of the 3D model (average under 0.001°). The angles are the ones you set on the machine. The 3D model is the same stone that you render or set.
The model measures 7.90 x 7.90 x 4.99 mm, which is 2.00 ct in diamond. At the same size, it weighs 1.83 ct in moissanite, 3.30 ct in cubic zirconia, 2.27 ct in ruby, 2.27 ct in sapphire, 1.55 ct in emerald, 1.51 ct in amethyst. You can scale it uniformly to any size: the weight follows the cube of the size.
Yes. The mesh is watertight and manifold, with outward normals and no duplicate vertices, so it prints and casts without repair. Use the STEP file when you need the exact faceted solid in CAD.
The Portuguese Bird's Nest Cut as exact geometry: 177 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
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.
Not sure the files open in your software? Get the cube free: the same six formats, for your email address, used only to send them (privacy).
Questions before you buy? Email us.