The Standard Round Brilliant and Some Common Variations
Standard Round Brilliant “Classic” – GemCad Derived Renderings by Bob Keller bkeller@rockhounds.com | |
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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 | |||
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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” | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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) | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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 | |
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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 | |||
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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. |