Gypsy
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Yssie... can I get your advice on these numbers.
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Gypsy
Super_Ideal_Rock
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Gypsy
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Dreamer_D
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You did not ask me, but I'll chime in anyways 
It is an interesting combination. The depth of the stone is fairly shallow for a old cut, and actually is more like a modern RB. The pavilion angke is also shallower than I would expect in an old cut, reflecting the depth I guess. The lower halves are short but not super short. But the crown is classic old cut in terms of its angle, though the table is not as small as we sometimes see on OECs. I think the end result will be a pretty balanced cut in terms of colored and white light, because we usually talk about how a shallower depth produces white light (a la a 60/60 type stone), but the steep crown and smaller table would suggest plenty of colored light.
Wait I am having deja vu, I might have already said all this somewhere else Ah well, still fun to discuss!
It is an interesting combination. The depth of the stone is fairly shallow for a old cut, and actually is more like a modern RB. The pavilion angke is also shallower than I would expect in an old cut, reflecting the depth I guess. The lower halves are short but not super short. But the crown is classic old cut in terms of its angle, though the table is not as small as we sometimes see on OECs. I think the end result will be a pretty balanced cut in terms of colored and white light, because we usually talk about how a shallower depth produces white light (a la a 60/60 type stone), but the steep crown and smaller table would suggest plenty of colored light.
Wait I am having deja vu, I might have already said all this somewhere else
Ah well, still fun to discuss!
Dreamer_D
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I didn't forget - I've just been disgustingly busy this week and my PSing has been limited to lurking by kindle
Okay, so - lots of ideas. Basically I'd agree with Dreamer, with some additions and caveats - my reasoning is simplistic but I don't have DiamCalc and DH would have my head if I splurged, so I've got exaggerated paper drafts, and anything involved at this level is kinda putting lipstick on a pig anyway... Sorry in advance if I ramble, and consider all appropriate disclaimers included...
Some articles that might be interesting -
(I used the dispersion curve on Pg2) http://www.gia.edu/research-resources/cut-microsite-pdfs/diamond-optics-part-2.pdf
http://www.gia.edu/research-resources/cut-microsite-pdfs/diamond-optics-part-1.pdf
http://www.pricescope.com/journal/fractioning_color_gem
One thing I learnt today: Tolkowski considered dispersion at only the final diamond-air boundary, as the ray exits the stone.
From the first article above -
Red (B line) : wavelength=690, Refractive Index N=2.407, CritAngle(CA)= arcsin(Nr/Ni)=24.57deg
Green (D line) : wavelength=590, N=2.417, CA=24.44deg
Violet (G line) : wavelength=430, N=2.452, CA=24.07deg
N(air)=1
Reflectivity = [(Ni-Nr)/(Ni+Nr)]^2 = [(1-2.42)/(1+2.42)]^2 ~ 17%
I'm just going to simplify the question and deal with coloured light first, it's easier to take care of what's there than to isolate what isn't! So, if I wanted to see lots of coloured light:
1. Better to have a flat exit surface or a curved one (made from many smaller angled flat surfaces) like your super high crown?
For diffuse lighting environments composed of infinite point sources better to have the combination of angled surfaces, because dispersions exiting near those angle boundaries are more likely to have room to travel forward without intersecting and interacting with other dispersions. Adjacent dispersions exiting a flat surface will eventually re-combine - *when* depends on how close they are, and what you see - whether you bisect a single dispersion and see colour or see an intersection or addition to white depends on how far away you are.
Better the curved surface in spotlights, too, for the same reasons, though it'd matter rather less since there are fewer individual dispersions so they already have some space.
Octonus ray tracing video w/ static pav and changing crown: http://www.cutstudy.com/cut/english/dc/images/movie/Diamond_RayTracing_CA=30-40_PA=40.70_crown-moving_size_400-400_100frames_10fps.gif
2. Better to have a shallow or steeper pavilion surface, considering only internal affairs?
This one's a bit more complicated. A pipe, for example, that allows TIR means that dispersions have endless opportunity to associate internally, so what meets the diamond-air exit surface is likely to be a white mumbo jumbo. A very shallow bowl on the other hand means fewer dispersions re-combine internally, so what meets the exit diamond-air bound is likely to be an unadulterated reflection of the initial entering refraction... Well, sorta. It depends on the specifics of the shape, too.
A deep 8-walled pyramid would allow more rays to not intersect than a deep 50-walled pyramid, which has many more internal surfaces and angled facet-meets at which adjacent rays immediately combine. And the area near the culet in an RB is a hub of activity, lots of primary rays pass through this region at least once - by cutting out a chunk of it with a large open culet you're avoiding a number of primary (and secondary and tertiary) path intersections -
First pic is a pink tourmaline w/ a blue culet from this thread [URL='https://www.pricescope.com/community/threads/calling-all-faceters-show-us-the-weird-ones.144623/']https://www.pricescope.com/community/threads/calling-all-faceters-show-us-the-weird-ones.144623/[/URL] - and it looks blue! Second is of my 0.8ct 60/60 type, I painted just culet w/ OPI California Raspberry, and it reflects around
Long lower halves that reach toward the culet decrease angular difference between adjacent pavilion facets, add facet area, add more angled facet-meet area, and basically transform the stone from a few-walled pyramid into a many-walled pyramid that facilitates white light return, given that if rays intersect sooner than later they're more likely to fully intersect - or partially intersect and propagate in strange ways - just because they're so much smaller in width/scope. All of which points to this thing being a fireball at non-over-obstructing distances.
BUT -
A shallow bowl by definition isn't deep, and with short lgfs it's like an 8-walled pyramid at the bottom, then a many-walled pyramid - lots of *spacing*, despite considerable angular difference around. There is, fundamentally, less angled facet-meet in this type of faceting pattern than in another type, like on the R. below vs. on the L. Those angled facet-meet lengths force internal dispersion intersection (whereas angled facet-meet lengths on the crown coax dispersion travel without intersection). Which means that in diffuse types of light there are fewer (certainly tertiary) internal reflections, and assuming this holds true for non-diffuse types of lights, it implies that many rays are coming to the exit diamond-air bound essentially intact, and with smaller dispersion spreads. Those spreads would increase when the ray actually exits but if they're smaller to start with your odds of catching "white" instead of colour *are* higher at a given distance X. And since there've been fewer internal reflections and so less energy loss at all those diamond/air meetings, the exiting rays are higher energy - more powerful, and more bright.
And it's not just how much angled facet-meet area there is, it's how it cuts across the facets, too - the pic on the L might show more overall facet-meet region, but those areas are close to each other, and leave lots of open space in the middle, so rays that hit near the facet-meet boundaries will intersect quickly, and rays that hit in the middle can travel further without interference. Assuming there's no crown - it's just pavilion with a flat top - there'd be a staggering of when you see white vs. when you see colour, depending on where you look and what distance you're looking from. In the stone on the R the facet-meets cut across the facets evenly, so rays would intersect more "evenly", for lack of better wording - so what you see (again assuming no crown material) is less staggering of where and when you see white vs. colour. So there should be, objectively, a region of space wherein you're able to see a *larger number* of intact dispersions through a variety of lighting coming from a stone with unevenly spaced out angled facet-meets than from a stone with evenly spaced angled facet-meets.
Then we add the fact that the more powerful emission is true of both white or coloured light output, and the fact that a higher-energy output is Brighter, and our eyes interpret Brighter as Lighter, and even Lighter as Whiter, and we wind up with
A) why stones with giant chunky facets seem to throw off pastels,
B) why what white exit refractions there are are super-powered, so bright and blinding that they're all you can focus on, and you might completely miss some other weaker coloured outputs,
C) That what the stone is doing and what our eyes interpret the stone to be doing aren't ever going to perfectly match!
So long story short - I agree with Dreamer, I think whatever the diamond is doing, what you SEE (from relatively far away) coming out through a variety of lighting types will be a mix of both white and colour at the same time, from different parts of the stone... as opposed to another type of stone which might have more of a split personality in those various lighting types. From up close when obstruction starts to kick in I imagine it's less balanced - either white or colour at a time, but with a decent chance of seeing either until the lighting gets extreme...
Well, that was definitely a ramble. Oh well. Thoughts, observations? Andrey how about diamcalc licenses for 15k posts?
Okay, so - lots of ideas. Basically I'd agree with Dreamer, with some additions and caveats - my reasoning is simplistic but I don't have DiamCalc and DH would have my head if I splurged, so I've got exaggerated paper drafts, and anything involved at this level is kinda putting lipstick on a pig anyway... Sorry in advance if I ramble, and consider all appropriate disclaimers included...
Some articles that might be interesting -
(I used the dispersion curve on Pg2) http://www.gia.edu/research-resources/cut-microsite-pdfs/diamond-optics-part-2.pdf
http://www.gia.edu/research-resources/cut-microsite-pdfs/diamond-optics-part-1.pdf
http://www.pricescope.com/journal/fractioning_color_gem
One thing I learnt today: Tolkowski considered dispersion at only the final diamond-air boundary, as the ray exits the stone.
From the first article above -
Red (B line) : wavelength=690, Refractive Index N=2.407, CritAngle(CA)= arcsin(Nr/Ni)=24.57deg
Green (D line) : wavelength=590, N=2.417, CA=24.44deg
Violet (G line) : wavelength=430, N=2.452, CA=24.07deg
N(air)=1
Reflectivity = [(Ni-Nr)/(Ni+Nr)]^2 = [(1-2.42)/(1+2.42)]^2 ~ 17%
I'm just going to simplify the question and deal with coloured light first, it's easier to take care of what's there than to isolate what isn't! So, if I wanted to see lots of coloured light:
1. Better to have a flat exit surface or a curved one (made from many smaller angled flat surfaces) like your super high crown?
For diffuse lighting environments composed of infinite point sources better to have the combination of angled surfaces, because dispersions exiting near those angle boundaries are more likely to have room to travel forward without intersecting and interacting with other dispersions. Adjacent dispersions exiting a flat surface will eventually re-combine - *when* depends on how close they are, and what you see - whether you bisect a single dispersion and see colour or see an intersection or addition to white depends on how far away you are.
Better the curved surface in spotlights, too, for the same reasons, though it'd matter rather less since there are fewer individual dispersions so they already have some space.
Octonus ray tracing video w/ static pav and changing crown: http://www.cutstudy.com/cut/english/dc/images/movie/Diamond_RayTracing_CA=30-40_PA=40.70_crown-moving_size_400-400_100frames_10fps.gif
2. Better to have a shallow or steeper pavilion surface, considering only internal affairs?
This one's a bit more complicated. A pipe, for example, that allows TIR means that dispersions have endless opportunity to associate internally, so what meets the diamond-air exit surface is likely to be a white mumbo jumbo. A very shallow bowl on the other hand means fewer dispersions re-combine internally, so what meets the exit diamond-air bound is likely to be an unadulterated reflection of the initial entering refraction... Well, sorta. It depends on the specifics of the shape, too.
A deep 8-walled pyramid would allow more rays to not intersect than a deep 50-walled pyramid, which has many more internal surfaces and angled facet-meets at which adjacent rays immediately combine. And the area near the culet in an RB is a hub of activity, lots of primary rays pass through this region at least once - by cutting out a chunk of it with a large open culet you're avoiding a number of primary (and secondary and tertiary) path intersections -
First pic is a pink tourmaline w/ a blue culet from this thread [URL='https://www.pricescope.com/community/threads/calling-all-faceters-show-us-the-weird-ones.144623/']https://www.pricescope.com/community/threads/calling-all-faceters-show-us-the-weird-ones.144623/[/URL] - and it looks blue! Second is of my 0.8ct 60/60 type, I painted just culet w/ OPI California Raspberry, and it reflects around
Long lower halves that reach toward the culet decrease angular difference between adjacent pavilion facets, add facet area, add more angled facet-meet area, and basically transform the stone from a few-walled pyramid into a many-walled pyramid that facilitates white light return, given that if rays intersect sooner than later they're more likely to fully intersect - or partially intersect and propagate in strange ways - just because they're so much smaller in width/scope. All of which points to this thing being a fireball at non-over-obstructing distances.
BUT -
A shallow bowl by definition isn't deep, and with short lgfs it's like an 8-walled pyramid at the bottom, then a many-walled pyramid - lots of *spacing*, despite considerable angular difference around. There is, fundamentally, less angled facet-meet in this type of faceting pattern than in another type, like on the R. below vs. on the L. Those angled facet-meet lengths force internal dispersion intersection (whereas angled facet-meet lengths on the crown coax dispersion travel without intersection). Which means that in diffuse types of light there are fewer (certainly tertiary) internal reflections, and assuming this holds true for non-diffuse types of lights, it implies that many rays are coming to the exit diamond-air bound essentially intact, and with smaller dispersion spreads. Those spreads would increase when the ray actually exits but if they're smaller to start with your odds of catching "white" instead of colour *are* higher at a given distance X. And since there've been fewer internal reflections and so less energy loss at all those diamond/air meetings, the exiting rays are higher energy - more powerful, and more bright.
And it's not just how much angled facet-meet area there is, it's how it cuts across the facets, too - the pic on the L might show more overall facet-meet region, but those areas are close to each other, and leave lots of open space in the middle, so rays that hit near the facet-meet boundaries will intersect quickly, and rays that hit in the middle can travel further without interference. Assuming there's no crown - it's just pavilion with a flat top - there'd be a staggering of when you see white vs. when you see colour, depending on where you look and what distance you're looking from. In the stone on the R the facet-meets cut across the facets evenly, so rays would intersect more "evenly", for lack of better wording - so what you see (again assuming no crown material) is less staggering of where and when you see white vs. colour. So there should be, objectively, a region of space wherein you're able to see a *larger number* of intact dispersions through a variety of lighting coming from a stone with unevenly spaced out angled facet-meets than from a stone with evenly spaced angled facet-meets.
Then we add the fact that the more powerful emission is true of both white or coloured light output, and the fact that a higher-energy output is Brighter, and our eyes interpret Brighter as Lighter, and even Lighter as Whiter, and we wind up with
A) why stones with giant chunky facets seem to throw off pastels,
B) why what white exit refractions there are are super-powered, so bright and blinding that they're all you can focus on, and you might completely miss some other weaker coloured outputs,
C) That what the stone is doing and what our eyes interpret the stone to be doing aren't ever going to perfectly match!
So long story short - I agree with Dreamer, I think whatever the diamond is doing, what you SEE (from relatively far away) coming out through a variety of lighting types will be a mix of both white and colour at the same time, from different parts of the stone... as opposed to another type of stone which might have more of a split personality in those various lighting types. From up close when obstruction starts to kick in I imagine it's less balanced - either white or colour at a time, but with a decent chance of seeing either until the lighting gets extreme...
Well, that was definitely a ramble. Oh well. Thoughts, observations? Andrey how about diamcalc licenses for 15k posts?
Dreamer_D
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mrssalvo
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Gypsy
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I liked the nail polished stone. Just the commitment of it, made me smile.
Thank you very much Yssie. I'm unfortunately not sure what you said, for the most part. I don't speak math and reflection theory. But it sounds like the stone is pretty good. And that's all I wanted a second (since I had Dreamers thoughts) opinion one.
Thank you very much Yssie. I'm unfortunately not sure what you said, for the most part. I don't speak math and reflection theory. But it sounds like the stone is pretty good. And that's all I wanted a second (since I had Dreamers thoughts) opinion one.
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Gypsy
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Yssie|1323319136|3076809 said:Gypsy|1323318803|3076801 said:
I'd buy it too... for some reason I thought you already had it!
I already bought it
. It's now been polished by BGD and the chip has been removed and replaced with a full faceted girdle. So I'm pretty happy. Good performance (head obstruction though it may show) and now it's been rehabbed. I only lost a point in weight to it too. So pretty happy.
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I'd be concerned with obstruction and darkness under the table. Shallow pavilion won't be helped by shorter halves it will make it more noticeable. Tall crown helps but not likely to completely remove your head reflection but do ask your cutter for thier input on this.
If you plan on wearing it as a pendant no problem.
Colored Light would be more noticeable than Tolk Round due to shorter lower halves and taller crown.
Gypsy
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Yssie|1323320052|3076820 said:
I have a couple. Brian wasn't there the day the stone was back from the recut, and I needed it sent to the setter ASAP so, the pictures are nice but not as nice as BGD's normal photography.
It does have obstruction under the table and shows darkness in some environments (and you can see it in the picture). But it is fine FOR ME on a ring-- it's MORE than beautiful enough for a ring. I wore it around on my fingers for three days before purchasing it. In all lighting conditions.
I don't expect an old cut stone to perform like an AV, I like the personality, and that includes the flashes of darkness under the table.
Dreamer_D
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Gypsy
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Dreamer_D
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The nice thing about obstruction is that it's only obstructing if there's something to obstruct it, and when there is that something is usually your head and usually neither it nor your finger are motionless So, really, a stone that's capable of getting blue all over with contrast is also capable of getting red with direct light and green with indirect light with a bit of tilt, so I'm not surprised it's a bright little creature when you move it around! And no mush... I loathe mush. I use a piece of printer paper with a grid of pinholes to photograph through sometimes, and stones look so awfully boring without any contrast.
So, really, a stone that's capable of getting blue all over with contrast is also capable of getting red with direct light and green with indirect light with a bit of tilt, so I'm not surprised it's a bright little creature when you move it around! And no mush... I loathe mush. I use a piece of printer paper with a grid of pinholes to photograph through sometimes, and stones look so awfully boring without any contrast.
Gypsy
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bmg|1323321847|3076846 said:Tilt it 10 degrees in any direction and I bet the mains under the table flash on as well. Am I right Gypsy?
Totally right bmg. It lights up when you move it. Really super bright. It's a stone that benefits from my shaking hands (I have pretty bad tension tremors at times). LOL.
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Past, Present, Future: The Meaning of Three-Stone Engagement Rings
Past, Present, Future: The Meaning of Three-Stone Engagement Rings - 04/14
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