Standard Round Brilliant with Spiked Mains
GemCad Derived Rendering by Bob Keller
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.
The SRB with Spiked Mains Design File is available for GemCad users.