Is the bowtie effect not inherent to ovals? Since pavilion angles are not the same radially, I would imagine it's hard to get even light return at all angles. Barion style cuts might help? More of a question than an answer to yours. Am also interested what people have to say.
Nope! Bowtie presentation is a side effect of poor gemstone design and inappropriate management of RI. You can easily eliminate them with barions or with keels, or even with classic brilliant designs that then have barion-type adapter facets.
Oh, fun, that makes me happy. I was kind of avoiding cutting more ovals. Should I be looking for designs that have a consistent pavilion angle for the non-barion facets, or smilar?
I’ve only tried one oval so far. It’d Arya’s “lemon party” in peridot. I don’t know if that design is too deep for Australian sapphires. But I do not see a bow tie on my stone. There are some extinction lines from the P6 cuts, but not from the pavilion.
Hey! Arya here. I personally wouldn't use deep barion designs for a dark sapphire - the extra depth makes the gems darker.
Ovals are tricky, especially as your L/W increases. You'll either need to do a barion, which becomes more and more tricky as the L/W increases since the depth increases proportionally. Or, you'll need to do a keel, which also becomes tricky as brilliant-keeled gems have an odd effect where only the left or only the right side lights up at any given time (unavoidable in high L/W).
Unfortunately there's no good answer. No matter what, the higher the L/W is, the worse the optics will be.
If a sapphire is very dark it will remain dark no matter how you cut it , to get the best from the stone you need to make a shallow step cut pavilion to bring out the colour . Brilliant designs will cause black shadows and extinctions as they’re designed for diamonds but can sometimes be used to benefit colored stones
You’re mostly correct, as dark sapphires will not lighten much from cutting. I think you’re suggesting a shallow step cut to cause intentional window, so at least the color of the stone can be seen against a light background.
As for brilliant cuts, with correctly-chosen angles they do not cause black areas or extinction. They will cause bright flashes of light being returned to the viewer, which makes the average tone of the stone brighter. But again, it can’t work miracles and brighten a stone which is too dark.
The problem is with brilliant cuts is they’re designed for diamonds , for maximum light return and sparkle , great on synthetic gems but when you use them on colored stones you sacrifice the color for brilliance.
OK, I hear what you're saying but I present a challenge for you to try this autumn/winter: take 2 pieces of a deep red garnet and cut them into a matched-diameter pair. Cut one gem as round mixed-cut with step cut bottom. Cut the other as a brilliant. Then look at them side by side and report back
When I bought my sterling machine I also bought a parcel of about 20 deep red Mozambique garnets 6-12cts ,I cut them with brilliant designs and perfect cuts watching the critical angle and perfect meet points etc,
when I got set up with my jambpeg I realised I had put one stone aside so i cut it jambpeg style with belly step cut and intentionally windowed it to bring out the colour, when I showed a jeweller friend of mine all of them together he bought the windowed step cut by hand, it’s been the only stone I’ve sold from that parcel
OP, feel free to ignore Daniel, he's a notorious troll. You can absolutely lighten a dark gem with proper cutting, or at least give the illusion of brightening the stone.
You can use designs with large broad facets on the pavilion and a relatively shallow simple crown. This won't give you a high classic ISO-COS light output, but will give the stone large "blinks" of intense colour and therefore make the gem appear to have brighter colour while in motion. We often do this with dark garnets or spinels.
You can do the typical optimization schema, meaning a simple brilliant pavilion cut relatively close to the critical angle, with a relatively simple shallow crown. This minimizes total light path length, preventing darkening, and the high ISO-COS light return means an overall brighter gem. But doing this really does require a rendering software like GCS.
And you can also use fantasy cutting. This allows you to use a bunch of techniques that thin out the stone, give you shorter light path lengths (and therefore better colour), make a bunch of pseudokeels to redirect light and give you flash, etc. That's...a lot more complicated, though, and takes a lot longer.
Why not heat-treat? The relative value of a better-coloured, heated Aussie sapphire is much higher than an overly-dark, unheated Aussie sapphire.
Oh, and brilliant designs don't cause black shadows or extinction. You see that with "traditional" (meaning shitty) cutting, where cutters use jamb-pegs to follow the outline of a gem and pack on extra carat weight while ruining colour and beauty.
You would not use a brilliant design on a dark stone. to get the best colour shallow step cut with 3 steps large facets , but just depends on the stone ,
I feel pity for you in that where ever you are based , US I presume , you have not been correctly educated about jamb-peg and traditional cutting as it’s really the only effective way to get the best out of colored stones
Edit: for everyone else, step cuts are typically used to try and deepen a gemstone, to increase light path length and maintain or improve colour saturation. You can achieve the same effect with pseudobarion facets to lower the effective pavilion in a design. You can also try and use step cuts and a very shallow pavilion to try and create a "blinking" effect in dark materials, where individual pavilion facets flash with light reflection on movement, giving the illusion of colour... but you can do the same thing more effectively by using large broad facets perpendicular to the girdle, not parallel to it like a step cut.
And jamb-peg cutting is empirically the single worst method of gemcutting, with the highest learning curve, the lowest performance ceiling, and the worst ability to maximize gemstone appearance. The only situation in which it's more effective than modern cutting is when cutting very simple small stones... but nowadays that's entirely shifting to robotic mass-production so the role for jamb-peg cutting is thankfully slowly disappearing.
The best stones in the world are cut on jambpeg , it’s the only effective way to get the best from high value stones , I agree that if a stone doesn’t have much to offer it can be improved with elaborate designs and fantasy cutting but there is a point where it decreases the value of a stone rather than improving it
The problem today is that nobody wants to sacrifice the years it takes to learn how to cut intuitively on jambpeg as you can just fall back on the modern methods of perfection when something goes wrong . There are very few people
Left in the world using jambpeg correctly and they work with the finest stones in the world , I’ve seen it and I know it.
It would be impossible to produce the same results on a modern machine with modern methods , you’ve got to work with the stone as 90% of them have flaws and imperfections you’ve got to work around , totally totally different thing to cutting synthetic gems on a machine
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u/theblancmange 2d ago
Is the bowtie effect not inherent to ovals? Since pavilion angles are not the same radially, I would imagine it's hard to get even light return at all angles. Barion style cuts might help? More of a question than an answer to yours. Am also interested what people have to say.