Bar Rounds by Bob Keller

I've recently begun considering how I might incorporate some of my faceting into jewelry for myself. A tie tack was one obvious candidate. However, I don't wear a tie often - they just don't integrate well with my Tucson "lifestyle". And when I do, nowadays it's almost always a bola. I've been considering how to incorporate some faceting in a bola, but most of my ideas for bolas involve using opaque materials. If I were 30 years younger I might make myself an earring, but here in Tucson, Arizona where you see a lot of cowboy boots, earrings tend to have connotations for guys my age that I'd rather avoid. I've already got the parrot, so when I do finally retire to the South Seas to a life of piracy...

In the meanwhile, I've been considering designing a ring for myself. Of course that had to involve designing the stone as well. The criteria include something different and which will throw broad flashes which are apparent at a distance. I've always liked deeply saturated red stones, but unfortunately my rough box is a little short in the ruby compartment. I figured adapting the design to some red tourmaline or garnet wasn't out of the question once I had refined it.

Bar Round I - designed by Bob Keller ©1999
Angles for R.I. = 1.54 37 facets + 16 facets on girdle = 53
2-fold symmetry 96 index
L/W = 1.000 T/W = 0.727 T/L = 0.727 P/W = 0.466 C/W = 0.237 H/W = (P+C)/W+0.02 = 0.723 P/H = 0.645 C/H = 0.327
Vol./W^3 = 0.260 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 49.9 ISO = 56.2

Pavilion
G1 90.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Cut to equal depth - set size
P1 43.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Meet G1 facets
Crown
C1 60.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Meet G1 facets, level girdle
C2 42.00 24-72 Meet corresponding G1 facets
C3 28.00 24-72 Meet C2, C1
C4 14.00 24-72 Meet C3, C1
T 0.00 Table Meet C4, C1

Bar Round I I'd been playing in GemCad with an idea for the crown of a round stone that employed a parallel set of bars cut across it in a manner forming an oval outline at their intersection with the break facets. It met the criteria of a different appearance and the bar facets would also throw broad surface flashes of reflected light as the stone moved to bring each one into play. I think simpler is often better, so my first approach at putting a pavilion under the crown on a proof stone employed a single tier of 16 facets.

I cut Bar Round I from a clear Mt. Ida point. It is 12mm in diameter and weighs about 6.0 carats. The raytrace wasn't particularly bright at the crown angles I used, but I wasn't too concerned about that with clear material. I was more interested in checking out the potential for reflective patterns and dispersion, and knew I could always make it brighter by lowering the crown. Bar Round I has the surface effect I was after, but the internal reflections and flashes were not as broad as I desired. I figured simply reducing the number of pavilion mains would provide broader flashes.

Shown at right is a very pretty Bar Round I cut from green YAG (yttrium aluminum garnet) by Dick Anderson of Bozeman Montana. YAG is a hard synthetic (8.5) with a relatively high refractive index of about 1.8 that works well with this design. YAG also has a fairly high specific gravity and Dick's 11mm stone weighs about 9 carats.

Bar Round IIa - designed by Bob Keller ©1999
Angles for R.I. = 1.54 45 facets + 16 facets on girdle = 61
2-fold symmetry 96 index
L/W = 1.000 T/W = 0.727 T/L = 0.727 P/W = 0.541 C/W = 0.237 H/W = (P+C)/W+0.02 = 0.798 P/H = 0.678 C/H = 0.296
Vol./W^3 = 0.323 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 59.8 ISO = 67.8

Pavilion
G1 90.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Cut to equal depth - set size
P1 70.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Meet G1 facets
P2 42.00 06-18-30-42-54-66-78-90 Cut to center point
Crown
C1 60.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Meet G1 facets, level girdle
C2 42.00 24-72 Meet corresponding G1 facets
C3 28.00 24-72 Meet C2, C1
C4 14.00 24-72 Meet C3, C1
T 0.00 Table Meet C4, C1

My next pass on GemCad produced the above variation for quartz, which halves the number of pavilion mains to eight, and adds a course of pavilion break facets to create a level girdle and provide a means of mounting at the cardinal indexes. I figured the stepped break facets on the pavilion could be cut at varying depths as dictated by the depth and saturation of the rough.

However, before I got around to proof cutting this variation I acquired a beautiful piece of rose Malaya garnet from Jeff Graham, large enough to cut a clean 10mm or better diameter stone. I had seen one of Jeff's SweetHearts cut from the same material and knew it would cut a superb red gem.

Bar Round IIb - designed by Bob Keller ©1999
Angles for R.I. = 1.72 37 facets + 16 facets on girdle = 53
2-fold symmetry 96 index
L/W = 1.000 T/W = 0.728 T/L = 0.728 P/W = 0.391 C/W = 0.194 H/W = (P+C)/W+0.02 = 0.605 P/H = 0.646 C/H = 0.321
Vol./W^3 = 0.220 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 75.2 ISO = 90.3

Pavilion
G1 90.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Cut to equal depth - set size
P1 38.00 06-18-30-42-54-66-78-90 Cut to equal depth - set culet center point
P2 50.00 96-12-24-36-48-60-72-84 Cut to meet G1 facets
Crown
C1 55.00 96-06-12-18-24-30-36-42-
48-54-60-66-72-78-84-90
Meet G1 facets, level girdle
C2 36.00 24-72 Meet corresponding G1 facets
C3 24.00 24-72 Meet C2, C1
C4 12.00 24-72 Meet C3, C1
T 0.00 Table Meet C4, C1

Synthetic Spinel Bar Round IIb Jeff's rhodolite began burning a hole in my rough box immediately, but I wasn't about to use it for proofing a new cut. Adapting the Bar Round design to the rhodolite required lowering the pavilion and crown angles to increase the brightness and generally optimizing it for deeply saturated material with a refractive index around 1.72.

Bar Round IIb incorporated those changes and the eight main pavilion. I selected some blue synthetic spinel to prototype this variation, as it was comparable to the garnet in terms of RI and saturation, and cut an 11mm stone weighing about 5.4 carats. With an ISO brightness of 90.3 this design has a lot of potential for deeply saturated material. And the eight fold pavilion mains definitely broadened up the internal flashes. However, to my eye not enough of the pavilion facets are "on" at the same time now, and I think some simple elaboration on the pavilion to increase the scintillation of this variation could improve it.

Rhodolite Garnet Bar Round IIbShown at left is an approximately 6.8 mm Bar Round IIb cut from rhodolite garnet by Norm Holbert of Norwich, Connecticut. Norm's Bar Round weighs about 1.3 carats.

While I was working on Bar Round IIb, some other faceters of my acquaintance at Old Pueblo Lapidary Club were cutting and showing off opposed bar cuts and checkerboards. Seeing their stones sparked my curiosity regarding the potential of the Bar Round crown for creating a similar effect when combined with a different pavilion.

Bar Round III - designed by Bob Keller ©1999
Angles for R.I. = 1.54 57 facets + 24 facets on girdle = 81
2-fold symmetry 96 index
L/W = 1.000 T/W = 0.714 T/L = 0.714 P/W = 0.450 C/W = 0.204 H/W = (P+C)/W+0.02 = 0.674 P/H = 0.668 C/H = 0.303
Vol./W^3 = 0.270 Brightness at 0 degrees tilt for R.I. = 1.54
COS = 58.2 ISO = 73.7

Pavilion
G1 90.00 96-04-08-12-16-20-24-28-32-36-40-44-
48-52-56-60-64-68-72-76-80-84-88-92
Cut to equal depth - set size
P1 42 24-72 Meet G1 - form level girdle
P2 42.98 20-28-68-76 Meet G1, P1 - form level girdle
P3 46.08 16-32-64-80 Meet G1, P2 - form level girdle
P4 51.73 12-36-60-84 Meet G1, P3 - form level girdle
P5 60.96 08-40-56-88 Meet G1, P4 - form level girdle
P6 67.79 04-44-52-92 Meet G1, P5 - form level girdle
P7 70.29 96-48 Meet G1, P6 - form level girdle
Crown
C1 55.00 96-04-08-12-16-20-28-32-36-40-44-
48-52-56-60-64-68-76-80-84-88-92
Meet G1, leave approx 2% girdle
C2 40.00 24-72 Meet G1, C1
C3 32.00 24-72 Meet C1, C2
C4 24.00 24-72 Meet C1, C3
C5 16.00 24-72 Meet C1, C4
C6 8.00 24-72 Meet C1, C5
T 0.00 Table Meet C1, C6

Bar Round III is the result of that curiosity. I couldn't resist and cut a 21 carat, 18mm prototype from clear Mt. Ida quartz. While the cut is not unattractive, the round shape and crescent facets interact with the checkerboard pattern created by opposed bar facets on the pavilion and crown, producing a pinched or hourglass distortion in the pattern.

I don't consider this variation particularly successful, as it doesn't stand and deliver on the intended rectilinear checkerboard effect. It is also on the more difficult to cut side with its long keel and paired bars on the pavilion. The keel is prone to chipping - this is remedied for the most part by cutting "into" or leading the lap rather than trailing it per normal practice. Making precise meets along the pavilion keel and girdle can also be challenging, especially on larger stones if your machine is not 'perfectly' aligned.

I think simply cutting a checkerboard crown is a lot more direct and surefire way to get that effect on a round stone. However, the checkers on a checkerboard crown are 'static' - they don't change size and shape the same way internally generated patterns can. To my eye, internal effects created by the interaction of multiple facets are the most elegant and interesting. Unfortunately, they also seem to be the most challenging and unpredictable to design.

Cutting Bar Round III has me interested now in exploring and playing with some opposed bar cuts. However, when I get to that I think I'll also morph my endeavors along those lines out of the Bar Rounds into designs with more rectilinear outlines.

I'm chomping at the bit to cut that rhodolite, but I also learn a great deal from the iterative, reality checking process that accompanies design refinement. I'm also convinced my faceting skills improve with each stone that I cut, although sometimes it doesn't seem that way. So I persuade myself and defer on the rhodolite with the theory that the longer I hold off cutting it, the better it's going to be...


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Bob Keller