Cutting strontium titanate
Strontium titanate has a refractive index of 2.409 and a dispersion of 0.190, a specific gravity of 5.13 and a hardness of 5 to 6 on the Mohs scale (cubic crystal system). It is singly refractive. Its critical angle, from the low end of the range, is 24.5°, so a round design needs a pavilion of at least 38.9° for head-on light to reflect off both sides of the pavilion and leave through the table.
We ray trace every cut in strontium titanate with the same light census that scores the other gemstones: one refractive index, 2.409, the midpoint of the published range, and a fire spread of 0.163, 0.86 of the published dispersion, the ratio our seven reference stones follow. Nothing is tuned to a result. Our instrument tools model strontium titanate too, except the dichroscope, polariscope and spectroscope, which need a measured spectrum; its figures live on this page, on each cut's page in strontium titanate, in the Cut Performance Wheel and in the Cut Performance Index.
Strontium titanate has nearly diamond's refractive index (2.409 against 2.417) with about four times its dispersion (0.190 against 0.044): light takes much the same paths as in diamond, and far more of it splits into color.
Strontium titanate optical properties
Published values, as on the strontium titanate glossary page; they change a little from stone to stone. Where a property has a range, we calculate angles from the lower refractive index. It gives the stricter limit. Sources: GIA · Gemdat · geology.com.
The top ten cuts in strontium titanate
In strontium titanate, the Portuguese Bird's Nest Cut performs best of the 23 jewelry cuts we score: 85 for brilliance, 98 for fire and 98 for scintillation. The Cushion Cut follows at 80, 95 and 85, then the Square Cut at 85, 95 and 78.
| Cut | Brilliance | Fire | Scintillation |
|---|---|---|---|
| Portuguese Bird's Nest, Jewelry cut | 85 (T73 benchmark 93) | 98 (T73 benchmark 98) | 98 (T73 benchmark 80) |
| Cushion, Jewelry cut | 80 (T73 benchmark 93) | 95 (T73 benchmark 98) | 85 (T73 benchmark 80) |
| Square, Jewelry cut | 85 (T73 benchmark 93) | 95 (T73 benchmark 98) | 78 (T73 benchmark 80) |
| Trilliant, Jewelry cut | 78 (T73 benchmark 93) | 96 (T73 benchmark 98) | 79 (T73 benchmark 80) |
| Marquise, Jewelry cut | 63 (T73 benchmark 93) | 93 (T73 benchmark 98) | 86 (T73 benchmark 80) |
| DG-Octagonal Kite, House cut | 88 (T73 benchmark 93) | 93 (T73 benchmark 98) | 60 (T73 benchmark 80) |
| Trillion, Jewelry cut | 67 (T73 benchmark 93) | 91 (T73 benchmark 98) | 80 (T73 benchmark 80) |
| Radiant Square, Jewelry cut | 72 (T73 benchmark 93) | 97 (T73 benchmark 98) | 66 (T73 benchmark 80) |
| Asscher, Jewelry cut | 69 (T73 benchmark 93) | 94 (T73 benchmark 98) | 72 (T73 benchmark 80) |
| Octagon, Jewelry cut | 72 (T73 benchmark 93) | 96 (T73 benchmark 98) | 66 (T73 benchmark 80) |
| Emerald Square, Jewelry cut | 64 (T73 benchmark 93) | 98 (T73 benchmark 98) | 72 (T73 benchmark 80) |
| Princess, Jewelry cut | 57 (T73 benchmark 93) | 99 (T73 benchmark 98) | 78 (T73 benchmark 80) |
In strontium titanate, the DG-Vitruvio Cut performs best of the 11 brilliants we score: 93 for brilliance, 98 for fire and 98 for scintillation. The DG-Miliano Cut follows at 95, 95 and 98, then the T105 Round Brilliant Cut at 95, 99 and 90.
| Cut | Brilliance | Fire | Scintillation |
|---|---|---|---|
| DG-Vitruvio, Brilliant | 93 (T73 benchmark 93) | 98 (T73 benchmark 98) | 98 (T73 benchmark 80) |
| DG-Miliano, House cut | 95 (T73 benchmark 93) | 95 (T73 benchmark 98) | 98 (T73 benchmark 80) |
| T105 Round Brilliant, Brilliant | 95 (T73 benchmark 93) | 99 (T73 benchmark 98) | 90 (T73 benchmark 80) |
| DG-M5, House cut | 97 (T73 benchmark 93) | 100 (T73 benchmark 98) | 85 (T73 benchmark 80) |
| DG-Rafaello, House cut | 94 (T73 benchmark 93) | 92 (T73 benchmark 98) | 96 (T73 benchmark 80) |
| DG-Broken Hearts and Arrows, Brilliant | 93 (T73 benchmark 93) | 98 (T73 benchmark 98) | 86 (T73 benchmark 80) |
| T73 Round Brilliant, Benchmark | 93 | 98 | 80 |
| DG-Anteros, Brilliant | 95 (T73 benchmark 93) | 95 (T73 benchmark 98) | 80 (T73 benchmark 80) |
| Old European, Historic cut | 90 (T73 benchmark 93) | 97 (T73 benchmark 98) | 81 (T73 benchmark 80) |
| T57 Round Brilliant, Historic cut | 92 (T73 benchmark 93) | 98 (T73 benchmark 98) | 72 (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 facets give as a stone moves, and we read it from the facets of each cut. We score 37 cuts, the same figures as our Cut Performance Index. The Cut Performance Wheel does not model this stone yet. Mazarin, Peruzzi and Old Mine, historic cushions, are in neither list. Each measured cut’s own page shows its figures in every gemstone we trace. A simulation of the geometry, not a grading report.
Strontium titanate: questions
What pavilion angle should I use for strontium titanate?
For a round design, at least 38.9°. At that angle or steeper, light that arrives straight down reflects off both sides of the pavilion, beyond the critical angle of strontium titanate (24.5°). Then it leaves through the table. The angle is the larger of the critical angle and (180° − critical angle) / 4. Faceters usually cut a degree or two steeper, for light that arrives off the axis. Fancy shapes vary, so every cut page lists its own figure.
What is the critical angle of strontium titanate?
24.5°, from a refractive index of 2.409, the low end of its published range. Light that strikes a facet from inside the stone at less than this angle from the normal of the facet passes out. At a larger angle, it reflects.
Which cuts work best in strontium titanate?
We add brilliance, fire and scintillation together. By that total, the DG-Vitruvio Cut, the DG-Miliano Cut and the T105 Round Brilliant Cut are the best brilliants in strontium titanate. By the same total, the best jewelry cuts are the Portuguese Bird's Nest Cut, the Cushion Cut and the Square Cut. We score 37 cuts in all, and this page ranks the top ten of each.
How much does strontium titanate weigh compared with diamond?
Strontium titanate has a specific gravity of about 5.13, and diamond has 3.52. So a stone of the same size weighs about 1.46 times as much as the diamond.