The Standard Round Brilliant and Some Common Variations

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The Standard Round Brilliant and Some Common Variations



Standard Round Brilliant “Classic” – GemCad Derived Renderings by Bob Keller bkeller@rockhounds.com
Angles for R.I. = 1.54 57 facets + 16 facets on girdle = 73
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.516 T/L = 0.516 P/W = 0.466 C/W = 0.218 H/W = (P+C)/W+0.02 = 0.704 P/H = 0.662 C/H = 0.309
Vol./W^3 = 0.236 Brightness at 0 degrees tilt for R.I. = 1.54 COS = 40.6% ISO = 46.5%

Pavilion
pb 45.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 43.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
Crown
cb 47.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 42.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 27.00 06-18-30-42-54-66-78-90 Cut to meet cm,cb
t 0.00 Table Cut to meet s,cm
This Standard Round Brilliant is shown with proportions and angles typical of that recommended for quartz in the classic literature such as Long and Steele’s. It has 8-fold symmetry, 8 pavilion main facets meeting at the culet, 16 pavilion break facets, 16 girdle facets, 16 crown break facets, 8 crown main facets, 8 star facets and 1 table facet which spans about 50 percent of the overall width at the girdle. Note that the height of the crown is approximately one-third of the overall height, and that the pavilion break facets extend approximately three-fifths of the distance from the girdle to the culet.

SRB Variation “Lowboy”

SRB Variation 'Lowboy'

SRB Variation “Lowboy”
Angles for R.I. = 1.54 57 facets + 16 facets on girdle = 73
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.546 T/L = 0.546 P/W = 0.435 C/W = 0.121 H/W = (P+C)/W+0.02 = 0.575 P/H = 0.755 C/H = 0.210
Vol./W^3 = 0.187 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 82.2% ISO = 87.2%
Pavilion
pb 43.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 41.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
Crown
cb 32.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 28.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 13.00 06-18-30-42-54-66-78-90 Cut to meet cm,cb
t 0.00 Table Cut to meet s,cm
The most fundamental variations of the SRB share the same indexes for all the facets but vary the angles with which they are cut. Design analysis done with raytracing and light modeling software demonstrates that lower angles are generally brighter angles within the performance envelopes. This ‘lowboy’ variation is cut with the pavilion mains at 41° – half a degree above the critical angle for quartz, and also employs substantially reduced crown angles compared to the ‘classic’ SRB. Note that the lower angles yield COS and ISO brightness values which are approximately double that of the classic, albeit arguably at the expense of other desirable properties.

SRB Variation with Unstacked Mains

SRB Variation with Unstacked Mains

SRB Variation with Unstacked Mains
Angles for R.I. = 1.54 57 facets + 16 facets on girdle = 73
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.477 T/L = 0.477 P/W = 0.466 C/W = 0.218 H/W = (P+C)/W+0.02 = 0.704 P/H = 0.662 C/H = 0.309
Vol./W^3 = 0.236 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 39.1% ISO = 44.2%
Pavilion
pb 45.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 43.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
Crown
cb 47.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 42.00 06-18-30-42-54-66-78-90 Cut to meet cb,g
s 27.00 96-12-24-36-48-60-72-84 Cut to meet cm,cb
t 0.00 Table Cut to meet s,cm
Another fundamental variation of the SRB ‘unstacks’ the pavilion and crown main facets, which are cut on the same indexes and ‘stacked’ in the classic version. This variation has no doubt been accidentally executed more than a few times by faceters who intended to cut the stacked version and somehow got off a cog when they aligned after transferring the stone.

SRB Variation with Spiked Mains

SRB Variation with 'Spiked' Mains

SRB Variation with Spiked Mains
Angles for R.I. = 1.54 57 facets + 16 facets on girdle = 73
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.559 T/L = 0.559 P/W = 0.458 C/W = 0.160 H/W = (P+C)/W+0.02 = 0.638 P/H = 0.718 C/H = 0.251
Vol./W^3 = 0.209 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 47.0% ISO = 50.9%
Pavilion
pb 43.50 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 42.50 96-12-24-36-48-60-72-84 Cut to meet pb,g
Crown
cb 42.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 36.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 22.00 06-18-30-42-54-66-78-90 Cut to meet cm,cb
t 0.00 Table Cut to meet s,cm
This simple variation of the SRB reduces the difference in elevation angle between the pavilion break and main facets from 2° in the classic version to 1° in the spiked mains variation, which produces deeper breaks and a tighter, more acutely shaped starburst pattern at the culet.

SRB Variation with Vertically Split Mains

SRB Variation with Vertically Split Mains

SRB Variation with Vertically Split Mains
Angles for R.I. = 1.54 73 facets + 16 facets on girdle = 89
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.597 T/L = 0.597 P/W = 0.449 C/W = 0.157 H/W = (P+C)/W+0.02 = 0.626 P/H = 0.717 C/H = 0.251
Vol./W^3 = 0.209 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 42.7% ISO = 56.8%
Pavilion
pb 44.50 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 42.00 01-11-13-23-25-35-37-47-49-59-61-71-73-83-85-95 Cut to meet pb,g
Crown
cb 42.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 38.00 01-11-13-23-25-35-37-47-49-59-61-71-73-83-85-95 Cut to meet cb,g
s 22.00 06-18-30-42-54-66-78-90 Cut to meet cm,cb
t 0.00 Table Cut to meet s,cm
This variation of the SRB doubles the number of main facets from 8 to 16 by splitting them vertically – instead of cutting 1 main facet at 96° as with the classic version, 2 main facets are cut at 95° and 1°, instead of 1 at 12°, 2 at 11° and 13° and so forth. The mains can be split on the pavilion only, crown only, or both. Adding more facets by splitting the mains increases the scintillation and is one way of adapting or scaling the SRB for use with larger stones.

SRB Variation with Horizontally Split Mains

SRB Variation with Horizontally Split Mains

SRB Variation with Horizontally Split Mains
Angles for R.I. = 1.54 73 facets + 16 facets on girdle = 89
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.528 T/L = 0.528 P/W = 0.487 C/W = 0.172 H/W = (P+C)/W+0.02 = 0.680 P/H = 0.717 C/H = 0.253
Vol./W^3 = 0.227 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 34.7% ISO = 38.2%
Pavilion
pb 47.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm1 45.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
pm2 43.00 96-12-24-36-48-60-72-84 Cut to meet pb, pm1
Crown
cb 47.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm1 38.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
cm2 34.00 96-12-24-36-48-60-72-84 Cut to meet cb,cm1
s 25.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm1,cm2
t 0.00 Table Cut to meet s,cm2
This variation of the SRB doubles the number of main facets from 8 to 16 by splitting them horizontally with the pairs of mains cut at the same index but different angles. The mains can be split on the pavilion only, crown only, or both. Adding more facets by splitting the mains increases the scintillation and is one way of adapting or scaling the SRB for use with larger stones.

SRB Variation – Mixed Cut with Pavilion Step at Girdle

SRB Variation - Mixed Cut with Pavilion Step at Girdle

SRB Variation – Mixed Cut with Pavilion Step at Girdle
Angles for R.I. = 1.54 73 facets + 16 facets on girdle = 89
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.529 T/L = 0.529 P/W = 0.578 C/W = 0.136 H/W = (P+C)/W+0.02 = 0.734 P/H = 0.788 C/H = 0.185
Vol./W^3 = 0.271 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 59.4% ISO = 63.2%
Pavilion
pb1 44.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
pb2 65.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb1
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb2
pm1 42.00 96-12-24-36-48-60-72-84 Cut to meet pb1,pb2
Crown
cb 34.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 30.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 15.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm
t 0.00 Table Cut to meet s,cm
This variation of the SRB adds a course of trapezoidal, relatively steep, step cut facets between the girdle and the triangular shaped pavilion break facets. It is considered to be a mixed cut, combining both step and brilliant cut facets. This cut can be useful for increasing yield and color saturation if you have deep rough. Steeper angles on the step cut will produce a brighter stone, but mounting practicalities generally dictate against extreme step angles.

SRB Variation – Mixed Cut with Step Framed Table

SRB Variation - Mixed Cut with Step Framed Table

SRB Variation – Mixed Cut with Step Framed Table
Angles for R.I. = 1.54 65 facets + 16 facets on girdle = 81
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.517 T/L = 0.517 P/W = 0.450 C/W = 0.113 H/W = (P+C)/W+0.02 = 0.584 P/H = 0.772 C/H = 0.194
Vol./W^3 = 0.189 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 72.2% ISO = 75.9%
Pavilion
pb1 44.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb2
pm1 42.00 96-12-24-36-48-60-72-84 Cut to meet pb1,pb2
Crown
cb 34.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 28.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 15.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm
f 10.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm
t 0.00 Table No meets!
This variation of the SRB adds a course of thin trapezoidal, step cut ‘frame’ facets between the table and the triangular shaped star facets. It is considered to be a mixed cut, combining both step and brilliant cut facets. Note that the table is not required to meet with the crown stars or mains when it is framed in this manner.

SRB Variation – Doubled Mains and Stars

SRB Variation - Doubled Mains and Stars

SRB Variation – Doubled Mains and Stars
Angles for R.I. = 1.54 81 facets + 16 facets on girdle = 97
16-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.618 T/L = 0.618 P/W = 0.442 C/W = 0.134 H/W = (P+C)/W+0.02 = 0.596 P/H = 0.742 C/H = 0.224
Vol./W^3 = 0.197 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 64.4% ISO = 68.1%
Pavilion
pb 42.50 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 41.50 96-06-12-18-24-30-36-42-48-54-60-66-72-78-84-90 Cut to meet pb,g
Crown
cb 38.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 35.00 96-06-12-18-24-30-36-42-48-54-60-66-72-78-84-90 Cut to meet cb,g
s 27.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet cb,cm
t 0.00 Table Cut to meet s,cm
This variation of the SRB doubles the number of main and star facets in each course. Note that in this variation the symmetry increases from 8 fold to 16 fold – there are 16 each pavilion main, pavilion break, girdle, crown break, crown main and star facets. Increasing the number of facets increases the scintillation and is a way of scaling up the SRB to work with larger stones.

SRB Variation – 12 Fold Symmetry

SRB Variation - 12 Fold Symmetry

SRB Variation – 12 Fold Symmetry
Angles for R.I. = 1.54 85 facets + 24 facets on girdle = 109
12-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.603 T/L = 0.603 P/W = 0.450 C/W = 0.139 H/W = (P+C)/W+0.02 = 0.609 P/H = 0.739 C/H = 0.228
Vol./W^3 = 0.203 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 62.8% ISO = 66.3%
Pavilion
pb 43.00 02-06-10-14-18-22-26-30-34-38-42-46-
50-54-58-62-66-70-74-78-82-86-90-94
Cut to temporary center point
g 90.00 02-06-10-14-18-22-26-30-34-38-42-46-
50-54-58-62-66-70-74-78-82-86-90-94
Cut to meet pb
pm 42.00 96-08-16-24-32-40-48-56-64-72-80-88 Cut to meet pb,g
Crown
cb 37.00 02-06-10-14-18-22-26-30-34-38-42-46-
50-54-58-62-66-70-74-78-82-86-90-94
Cut to meet g – level girdle
cm 35.00 96-08-16-24-32-40-48-56-64-72-80-88 Cut to meet cb,g
s 18.00 04-12-20-28-36-44-52-60-68-76-84-92 Cut to meet cb,cm
t 0.00 Table Cut to meet s,cm
This variation of the SRB increases the number of facets in each course by 50% by increasing the symmetry from 8 fold to 12 fold. Increasing the number of facets increases the scintillation and is a way of scaling up the SRB to work with larger stones.

SRB Variation – 16 Fold Symmetry

SRB Variation - 16 Fold Symmetry

SRB Variation – 16 Fold Symmetry
Angles for R.I. = 1.54 113 facets + 32 facets on girdle = 145
16-fold, mirror-image symmetry 64 index
L/W = 1.000 T/W = 0.629 T/L = 0.629 P/W = 0.442 C/W = 0.109 H/W = (P+C)/W+0.02 = 0.572 P/H = 0.774 C/H = 0.191
Vol./W^3 = 0.186 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 89.8% ISO = 93.8%
Pavilion
pb 42.00 01-03-05-07-09-11-13-15-17-19-21-23-25-27-29-31-
33-35-37-39-41-43-45-47-49-51-53-55-57-59-61-63
Cut to temporary center point
g 90.00 01-03-05-07-09-11-13-15-17-19-21-23-25-27-29-31-
33-35-37-39-41-43-45-47-49-51-53-55-57-59-61-63
Cut to meet pb
pm 41.50 64-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60 Cut to meet pb,g
Crown
cb 32.00 01-03-05-07-09-11-13-15-17-19-21-23-25-27-29-31-
33-35-37-39-41-43-45-47-49-51-53-55-57-59-61-63
Cut to meet g – level girdle
cm 30.50 64-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60 Cut to meet cb,g
s 25.00 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62 Cut to meet cb,cm
t 0.00 Table Cut to meet s,cm
This variation of the SRB doubles the number of facets in each course by increasing the symmetry from 8 fold to 16 fold. Increasing the number of facets increases the scintillation and is a way of scaling up the SRB to work with larger stones. Note that this variation is cut with a 64 index.

SRB Variation – 6 Fold Symmetry – Split crown mains

SRB Variation - 6 Fold Symmetry - Split Crown Mains

SRB Variation – 6 Fold Symmetry – Split Crown Mains
Angles for R.I. = 1.54 49 facets + 12 facets on girdle = 61
6-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.352 T/L = 0.352 P/W = 0.435 C/W = 0.194 H/W = (P+C)/W+0.02 = 0.649 P/H = 0.670 C/H = 0.299
Vol./W^3 = 0.206 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 62.6% ISO = 68.7%
Pavilion
pb 43.00 04-12-20-28-36-44-52-60-68-76-84-92 Cut to temporary center point
g 90.00 04-12-20-28-36-44-52-60-68-76-84-92 Cut to meet pb
pm 41.00 96-16-32-48-64-80 Cut to meet pb,g
Crown
cb 38.00 04-12-20-28-36-44-52-60-68-76-84-92 Cut to meet g – level girdle
cm1 32.00 08-24-40-56-72-88 Cut to meet cb,g
cm2 28.00 08-24-40-56-72-88 Cut to meet cb,cm1
s 18.00 96-16-32-48-64-80 Cut to meet cb,cm1,cm2
t 0.00 Table Cut to meet s,cm2
This variation of the SRB decreases the number of facets in each course by 25% by decreasing the symmetry from 8 fold to 6 fold. Decreasing the number of facets decreases the scintillation and is a way of scaling down the SRB to work with smaller stones. This variation also employs unstacked, horizontally split crown mains.

SRB Variation – Apex Facets Replacing Table

SRB Variation - Apex Facets Replacing Table

SRB Variation – Apex Facets Replacing Table
Angles for R.I. = 1.54 64 facets + 16 facets on girdle = 80
8-fold, mirror-image symmetry 96 index
L/W = 1.000 P/W = 0.405 C/W = 0.155 H/W = (P+C)/W+0.02 = 0.580 P/H = 0.698 C/H = 0.268
Vol./W^3 = 0.180 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 88.4% ISO = 93.8%
Pavilion
pb 41.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 39.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
Crown
cb 34.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 28.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 15.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm
a 10.00 06-18-30-42-54-66-78-90 Cut to meet s,cm
This variation of the SRB replaces the table with apex facets. Apex facets are smaller and easier to polish on larger stones. The angled apex facets refract incident light at a different angle internally than a 0° table, allowing further reduction in the angles of the pavilion facets to values that would dump light and ‘fisheye’ or ‘window’ with a conventional table. Note the brightness figures for this variation and angles employed.

SRB Variation – Pavilion Star (Zircon Cut)

SRB Variation - Pavilion Star (Zircon Cut)

SRB Variation – Pavilion Star (Zircon Cut)
Angles for R.I. = 1.54 73 facets + 16 facets on girdle = 89
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.516 T/L = 0.516 P/W = 0.462 C/W = 0.218 H/W = (P+C)/W+0.02 = 0.700 P/H = 0.660 C/H = 0.311
Vol./W^3 = 0.236 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 41.1% ISO = 46.6%
Pavilion
pb 45.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 43.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
z 41.00 02-10-14-22-26-34-38-46-50-58-62-70-74-82-86-94 Cut to meet pm,culet
Crown
cb 47.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 42.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 27.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm
t 00.00 table Cut to meet s,cm
This variation of the SRB adds an extra course of facets to the pavilion at the culet, forming a starburst pattern and adding an embellishing accent. In the variation illustrated the accent facets are split vertically, and it is often referred to as the ‘Zircon Cut’ variation of the SRB.

SRB Variation – Pavilion Star Frosted or Dark

SRB Variation - Pavilion Star Frosted or Dark

SRB Variation – Pavilion Star Frosted or Dark
Angles for R.I. = 1.54 65 facets + 16 facets on girdle = 81
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.543 T/L = 0.543 P/W = 0.442 C/W = 0.137 H/W = (P+C)/W+0.02 = 0.600 P/H = 0.738 C/H = 0.229
Vol./W^3 = 0.195 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 64.2% ISO = 68.3%
Pavilion
pb 43.50 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to temporary center point
g 90.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet pb
pm 42.00 96-12-24-36-48-60-72-84 Cut to meet pb,g
f 38.00 06-18-30-42-54-66-78-90 Cut to meet pm,culet
Crown
cb 36.00 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 Cut to meet g – level girdle
cm 31.00 96-12-24-36-48-60-72-84 Cut to meet cb,g
s 18.00 06-18-30-42-54-66-78-90 Cut to meet cb,cm
t 00.00 table Cut to meet s,cm
This variation of the SRB adds an extra course of facets to the pavilion, forming a starburst pattern and adding an embellishing accent at the culet. In the variation illustrated the accent facets are cut below the critical angle so they will intentionally window and create a ‘dark star’ accent when they are polished. These facets can also be left unpolished to create a frosted effect on the culet accent.

SRB Variation – Highlight Breaks

SRB Variation - Highlight Breaks

SRB Variation – Highlight Breaks
Angles for R.I. = 1.54 73 facets + 24 facets on girdle = 97
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.508 T/L = 0.508 P/W = 0.450 C/W = 0.154 H/W = (P+C)/W+0.02 = 0.624 P/H = 0.721 C/H = 0.246
Vol./W^3 = 0.205 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 66.5% ISO = 70.8%
Pavilion
g 90.00 02-06-10-14-18-22-26-30-34-38-42-46-
50-54-58-62-66-70-74-78-82-86-90-94
Cut to equal depth, establish size
pm 42.00 96-12-24-36-48-60-72-84 Cut to equal depth, establish girdle
pb 43.00 02-10-14-22-26-34-38-46-50-58-62-70-74-82-86-94 Meet g,pm
ph 43.53 06-18-30-42-54-66-78-90 Meet g,pb,pm
Crown
cm 32.00 96-12-24-36-48-60-72-84 Cut to equal depth – establish upper girdle line
cb 34.50 02-10-14-22-26-34-38-46-50-58-62-70-74-82-86-94 Cut to meet g,cm
ch 36.22 06-18-30-42-54-66-78-90 Cut to meet g,cb
s 18.00 06-18-30-42-54-66-78-90 Cut to meet ch,cb,cm
t 00.00 table Cut to meet s,cm
This variation of the SRB splits the break facets with a third facet instead of a single dividing ridge. Note there are 24 equal girdle segments in this variation instead of the usual 16 with an 8-fold symmetry SRB. Adding more facets by “fanning out” the breaks increases the scintillation and is one way of adapting or scaling the SRB for use with larger stones.

SRB Variation – Highlight Breaks and Stars

SRB Variation - Highlight Breaks and Stars

SRB Variation – Highlight Breaks and Stars
Angles for R.I. = 1.54 89 facets + 24 facets on girdle = 113
8-fold, mirror-image symmetry 96 index
L/W = 1.000 T/W = 0.592 T/L = 0.592 P/W = 0.450 C/W = 0.128 H/W = (P+C)/W+0.02 = 0.598 P/H = 0.753 C/H = 0.213
Vol./W^3 = 0.199 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 69.9% ISO = 73.6%
Pavilion
g 90.00 02-06-10-14-18-22-26-30-34-38-42-46-
50-54-58-62-66-70-74-78-82-86-90-94
Cut to equal depth, establish size
pm 42.00 96-12-24-36-48-60-72-84 Cut to equal depth, establish girdle
pb 43.00 02-10-14-22-26-34-38-46-50-58-62-70-74-82-86-94 Meet g,pm
ph 43.53 06-18-30-42-54-66-78-90 Meet g,pb,pm
Crown
cm 32.00 96-12-24-36-48-60-72-84 Cut to equal depth – establish upper girdle line
cb 35.50 02-10-14-22-26-34-38-46-50-58-62-70-74-82-86-94 Cut to meet g,cm
ch 38.09 06-18-30-42-54-66-78-90 Cut to meet g,cb
s 24.00 02-10-14-22-26-34-38-46-50-58-62-70-74-82-86-94 Cut to meet ch,cb,cm
sh 20.60 06-18-30-42-54-66-78-90 Cut to meet s,ch,cb,cm
t 00.00 table Cut to meet s,cm
This variation of the SRB ‘highlights’ the stars in addition to splitting the break facets with a third facet instead of a single dividing ridge. Note there are 24 equal girdle segments in this variation instead of the usual 16 with an 8-fold symmetry SRB. Adding more facets by “fanning out” the breaks and stars increases the scintillation and is one way of adapting or scaling the SRB for use with larger stones.