Old Mine Cut Demantoid: what our light census measures
Brilliance 56 · Fire 78 · Scintillation 81 · in our census, where the T73 scores 97 · 84 · 80 in demantoid
How the Old Mine Cut handles light in demantoid, measured: brilliance 56, fire 78 and 41% leakage, set against the T73 in the same stone and against the same cut in diamond.
Light Return map of the Old Mine Cut in demantoid, face-up, from our own tracer at refractive index 1.881. Red, green and blue return light to the eye; gray leaks.
Old Mine Cut Demantoid
Demantoid has a refractive index of 1.881 to 1.888 and a dispersion of 0.057. Its critical angle, from the low end of that range, is 32.1°, so a round design needs a pavilion of at least 37.0° for head-on light to reflect off both sides of the pavilion and leave through the table. We trace it with one index, 1.885, the midpoint of the published range, and a fire spread of 0.049, 0.86 of the published dispersion. Every picture here is our Light Return tracer at 1.881, and every figure is from the same light census that scores the other gemstones; the 3D Gemstone Simulator shows the Old Mine Cut in demantoid live.
The Old Mine Cut has 74 facets, a table of 60.3% of its width and a total depth of 65.6% of its width; its pavilion mains sit at 44.4°. In demantoid, the census returns 56 of 100 for brilliance and 78 for fire, against 97 and 84 for the T73, our benchmark, in the same stone; the same Old Mine Cut in diamond reads 59 and 72.
Is demantoid good in an Old Mine? Pros and cons, measured
Compared with the T73 Round Brilliant in demantoid and with the Old Mine 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.
All eight scores against the T73
At a glance: the Old Mine Cut in demantoid (white) against the T73 Round Brilliant in demantoid (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 demantoid: ahead on 2, behind on 6.
Global74, the comparison 90, difference −16
Brilliance56, the comparison 97, difference −41
Fire78, the comparison 84, difference −6
Scintillation81, the comparison 80, difference +1
Spread98, the comparison 100, difference −2
Symmetry90, the comparison 100, difference −10
Shape-norm88, the comparison 104, difference −16
Tilt100, the comparison 79, difference +21
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; these are the same census figures as our Cut Performance Index.
What the Old Mine Cut gains in demantoid
Against the T73 in demantoid and the same cut in diamond, no figure of the Old Mine Cut is ahead by the thresholds above. Its figures are in the wheel and the FAQ; Demantoid ranks every cut we score in demantoid.
What the Old Mine Cut gives up in demantoid
Returns less light than the T73 in demantoid
Brilliance 56 against 97 for the T73 Round Brilliant in demantoid: 41 points lower
Brilliance is the share of the 3,200 census rays that enter the stone and come back out of the crown towards the viewer. In demantoid, whose critical angle is 32.1°, the Old Mine Cut returns 56 of 100 and the T73 97. The Old Mine Cut's pavilion mains sit at 44.4°, the T73's at 40.8°. The maps below show where each stone's light returns from and where it leaks.
Old Mine Cut in demantoid · Brilliance 56
T73 Round Brilliant in demantoid · Brilliance 97
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.
Leakage 41 against 3 for the T73 Round Brilliant in demantoid: 38 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 Old Mine Cut leaks 41% in demantoid against 3% for the T73 in demantoid. Grey in the maps below is leaking light; the share under each picture is that picture's own.
Old Mine Cut in demantoid · Leakage 41
0° · 45% leak
10° · 39% leak
20° · 30% leak
30° · 33% leak
T73 Round Brilliant in demantoid · Leakage 3
0° · 1% leak
10° · 6% leak
20° · 17% leak
30° · 29% 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.
Symmetry 90 against 100 for the T73 Round Brilliant in demantoid: 10 points lower
Symmetry reads how evenly the pavilion facets of each design family are cut: 100 − 6 × their scatter in degrees. The Old Mine Cut reads 90, the T73 100. It depends on the geometry alone, so it is the same in every stone.
Old Mine Cut · 74 facets · Symmetry 90
T73 Round Brilliant · 73 facets · Symmetry 100
Symmetry scores how regular the pavilion facets are within the design. Compare how evenly the facets repeat around each pavilion. Drawn from each cut's own model.
1.32 ct at 6.5 mm, against 1.21 ct for the same cut in diamond (+9%)
Weight follows specific gravity: 3.85 for demantoid against 3.52 for diamond, so the same model at the same size weighs 1.32 ct here and 1.21 ct in diamond, 6.5 mm across. Nothing about the light changes with it.
A Old Mine Cut 6.5 mm across, weighed from the model's measured volume and each stone's specific gravity.
Against the T73 in demantoid and the same cut in diamond, no figure of the Old Mine Cut is ahead by our thresholds. The catch: it returns less light than the T73, leaks more light than the T73, has a less regular pavilion than the T73 and weighs more than in diamond.
If that catch matters more to you, the DG-Broken Hearts and Arrows reads 97 for brilliance in demantoid, 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 Old Mine Cut model we traced.
Old Mine Cut Demantoid: questions
Is the Old Mine a good cut for demantoid?
In our census the Old Mine Cut returns 56 of 100 for brilliance and 78 for fire in demantoid, against 97 and 84 for the T73 in the same stone. Against that round and against the same cut in diamond it has 0 pros and 4 cons by our thresholds; the summary above names them.
What pavilion angle does demantoid need?
At least 37.0° for a round design: demantoid's critical angle is 32.1°, 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 Old Mine Cut's pavilion mains sit at 44.4°.
How much does a Old Mine weigh in demantoid?
At 6.5 mm across, 1.32 ct in demantoid, against 1.21 ct for the same cut in diamond (+9%): demantoid's specific gravity is 3.85, diamond's 3.52.
Can I see the Old Mine in demantoid in 3D?
Yes: the 3D Gemstone Simulator renders it live, with demantoid's own refractive index and dispersion. Demantoid 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 Old Mine Cut files
6 formatsMillimetersWatertight
Old Mine Cut 3D files
The Old Mine Cut as exact geometry: 74 planar facets, real-world scale, ready for CAD,
rendering, printing and casting.
Save with a bundle: the Old Mine Cut 3D and cutting files are also in Historic Cuts Complete, 6 cuts for €29.99 until 1 December, then €39.99 (€101.88 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).
