3D model and faceting diagram · 73 facets · 8.15 x 8.15 mm
The same 1919 round brilliant proportions as the T57, with a sixteen-facet girdle band: 57 facets plus 16 girdle facets. Most round brilliants are finished this way today.
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The same 1919 round brilliant proportions as the T57, with a sixteen-facet girdle band: 57 facets plus 16 girdle facets. Most round brilliants are finished this way today.
Choose it when you want the published proportions and a girdle that a setter can seat and a polisher will recognize.
Measured from the delivered model, not quoted from a standard.
The T73 Round Brilliant Cut performs best in cubic zirconia, where its brilliance and fire together are highest: 98 for brilliance and 87 for fire. Its fire peaks in moissanite, at 97. In diamond it scores 93 for brilliance and 78 for fire. It is the benchmark that the Cut Performance Wheel compares every cut with. Its scintillation, 80, comes from its pattern of facets, so it is the same in every stone.
| Gemstone | Brilliance | Fire | Scintillation |
|---|---|---|---|
| Diamond | 93 | 78 | 80 |
| Moissanite | 86 | 97 | 80 |
| Cubic Zirconia | 98 | 87 | 80 |
| Ruby | 94 | 37 | 80 |
| Sapphire | 94 | 37 | 80 |
| Emerald | 78 | 39 | 80 |
| Amethyst | 72 | 36 | 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 T73 Round Brilliant 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.
| Stone | Refractive index | Critical angle | Pavilion reflecting head-on light | Weight at this size | Verdict |
|---|---|---|---|---|---|
| Diamond | 2.417 | 24.4° | 100% | 1.99 ct | Holds head-on light |
| Moissanite | 2.648 to 2.691 | 22.2° | 100% | 1.82 ct | Holds head-on light |
| Cubic Zirconia | 2.15 to 2.18 | 27.7° | 100% | 3.28 ct | Holds head-on light |
| Ruby | 1.762 to 1.770 | 34.6° | 100% | 2.26 ct | Holds head-on light |
| Sapphire | 1.762 to 1.770 | 34.6° | 100% | 2.26 ct | Holds head-on light |
| Emerald | 1.577 to 1.583 | 39.4° | 100% | 1.54 ct | Holds head-on light |
| Amethyst | 1.544 to 1.553 | 40.4° | 100% | 1.50 ct | Holds head-on light |
Head-on light, first reflection. The 3D Gemstone Simulator traces the full Light Return in each of these gemstones.
The T73 Round Brilliant 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 73 planar facets.
Yes. The cutting files contain a GemCad .asc design (57 + 16 girdles = 73 facets, 96 index, 8-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, Emerald, Amethyst, the whole pavilion reflects head-on light.
We check it facet by facet against the 3D model that it was written from. Every crown and pavilion facet within 0.009° of the 3D model (average under 0.001°); girdle facets within 0.016°. 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 8.15 x 8.15 x 5.03 mm, which is 1.99 ct in diamond. At the same size, it weighs 1.82 ct in moissanite, 3.28 ct in cubic zirconia, 2.26 ct in ruby, 2.26 ct in sapphire, 1.54 ct in emerald, 1.50 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.
Free lessons that use this cut, with videos where they have one.
The T73 Round Brilliant Cut as exact geometry: 73 planar facets, real-world scale, ready for CAD, rendering, printing and casting.
The T73 Round Brilliant Cut as a faceting design: 57 + 16 girdles = 73 facets, 96 index, 8-fold mirror-image symmetry, ready for the machine.
Save with a bundle: the T73 Round Brilliant Cut 3D files are also in Jewelry Essentials 3D, 10 cuts for €29.99 until 1 December, then €39.99 (€99.90 as single files). Buy the bundle.
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.