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cut tech thread: virtual facet size

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strmrdr

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Something that Iv been thinking about is virtual facet size vs viewing distance.
Peter talking about virtual facets in the vid and Garry''s discussion of shallow stones got me thinking about it.

For example are larger virtual facet sizes an advantage in the longer viewing distance when mounted in pendants and earrings.
I do know that a well cut asscher when moved can send out a huge flash of attention getting fire, larger than pretty much any other diamond Iv seen.

As distance increases the eyes ability to separate fine details rapidly falls off.

2nd part of the question would be: virtual facet size and fire, it seems like the stones with large virtual facets Asschers, EC and oec mostly return fire but are not the brightest stones around.
Do larger virtual facets decrease white light return and increase fire?

3rd part and if I had DC working I would look into it:
What has the greatest effect on virtual facet size in the standard RB cut?
lgf% is one.
Does high crowns with shallow pavilions increase them?
 

adamasgem

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Date: 12/20/2006 11:57:47 AM
Author:strmrdr
Something that Iv been thinking about is virtual facet size vs viewing distance.
Peter talking about virtual facets in the vid and Garry''s discussion of shallow stones got me thinking about it.

For example are larger virtual facet sizes an advantage in the longer viewing distance when mounted in pendants and earrings.
I do know that a well cut asscher when moved can send out a huge flash of attention getting fire, larger than pretty much any other diamond Iv seen.

As distance increases the eyes ability to separate fine details rapidly falls off.

2nd part of the question would be: virtual facet size and fire, it seems like the stones with large virtual facets Asschers, EC and oec mostly return fire but are not the brightest stones around.
Do larger virtual facets decrease white light return and increase fire?

3rd part and if I had DC working I would look into it:
What has the greatest effect on virtual facet size in the standard RB cut?
lgf% is one.
Does high crowns with shallow pavilions increase them?
The greatest effects are due to the general lack of opticall symmetry and mis-alignments. I haveshown this in my fire performance photos..where you see broadflash fire, every real facet lighting up with one purer color, instead of smaller areas of color of muted colors
 

Regular Guy

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Sorry for the sidebar, but...does "optical symmetry" vary one to one, or randomly, with physical and meet point symmetry, as a) you mean it and b) as I hope is it is meant as it is also discussed here.

If one to one, or close to it...is this just a situation of talking about: me, myself & I, from the point of view of different aspects? I''m guessing these are different...enough...causing the differential in language.

But even if not one to one...won''t there be a relationship between all three? A likelihood that high symmetry in one will suggest high symmetry in the other?

Many thanks!
 

Garry H (Cut Nut)

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Date: 12/20/2006 11:57:47 AM
Author:strmrdr


3rd part and if I had DC working I would look into it:
What has the greatest effect on virtual facet size in the standard RB cut?
lgf% is one.
Does high crowns with shallow pavilions increase them?
High crown shallow pav = FIC = more virtual facets because the greater interactions with the pavilion.

At a greater distance the visible flashes of fire become more distinct because there is less mixing of colors on the retina. Closer up though we can see more virtual smaller facets that become impossible to resolve otherwise.

Sergey is working on contrast to account for this in a beta verrsion of DiamCalc that i sam using - it is much better - but still not quite sure about it. It is ''normalized'' to tolkowsky results for the same sized stone.
 

adamasgem

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Date: 12/20/2006 12:38:08 PM
Author: Regular Guy
Sorry for the sidebar, but...does ''optical symmetry'' vary one to one, or randomly, with physical and meet point symmetry, as a) you mean it and b) as I hope is it is meant as it is also discussed here.

If one to one, or close to it...is this just a situation of talking about: me, myself & I, from the point of view of different aspects? I''m guessing these are different...enough...causing the differential in language.

But even if not one to one...won''t there be a relationship between all three? A likelihood that high symmetry in one will suggest high symmetry in the other?

Many thanks!
Ira.. There are some catch 22''s..
1) Because of mesurement errors, what may in actuality be perfect physical symmetry may not show up as so in scanners
2) Perfect physical symmetry MAY NOT show up as perfect optical symmetry because of strain
3) Slightly imperfect physical symmetry can be balanced by cutting compensation to produce virtual optical symmetry

In a strain free stone, perfect physical symmetry = perfect optical symmetry
 

Regular Guy

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Thanks, Marty. And...do either of these 2 types of symmetry map onto the labels for symmetry given by the labs (meet point symmetry?).

...and p.s. how common or uncommon is strain? Generally? And, is it reported on a lab report? How would it be observed?
 

adamasgem

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Date: 12/20/2006 4:51:58 PM
Author: Regular Guy
Thanks, Marty. And...do either of these 2 types of symmetry map onto the labels for symmetry given by the labs (meet point symmetry?). I don''t believe so, in general. Bill Bray''s Brayscore takes into account the workmanship issues such as this.

...and p.s. how common or uncommon is strain? Generally? I think Rockdoc would have some better comments on that issue. And, is it reported on a lab report? No How would it be observed? Crossed polars ie with a Polariscope, better under a microscope with crossed polars
 

Garry H (Cut Nut)

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Date: 12/20/2006 4:05:54 PM
Author: adamasgem

2) Perfect physical symmetry MAY NOT show up as perfect optical symmetry because of strain

In a strain free stone, perfect physical symmetry = perfect optical symmetry
Marty we had some great debates on the ''strain'' issue some years back.

Strain causes such a slight difference in Refractive Index of diamonds as to make a visible difference if one were to be examining a diamond on earth from the moon (with such a huge telescope, that would infact negate the effect anyway).

Sergey and Yuri weighed in with evidence to support this - so please read some of the old threads before we raise this debate again.
 

JohnQuixote

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Date: 12/20/2006 12:38:08 PM
Author: Regular Guy
Sorry for the sidebar, but...does ''optical symmetry'' vary one to one, or randomly, with physical and meet point symmetry, as a) you mean it and b) as I hope is it is meant as it is also discussed here.

That explanation celebrated its two-year anniversary last month. Since then I''ve developed better graphics and elaboration (including mention of the Firescope, which was the first popularized optical symmetry device). I''ll post the new version in this thread.

* Leonid - the info Ira linked can''t be added-to now. If you deem the post below better-suited to replace it, please move it there at your leisure. Thanks.
 

adamasgem

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Date: 12/20/2006 5:12:38 PM
Author: Garry H (Cut Nut)

Date: 12/20/2006 4:05:54 PM
Author: adamasgem

2) Perfect physical symmetry MAY NOT show up as perfect optical symmetry because of strain

In a strain free stone, perfect physical symmetry = perfect optical symmetry
Marty we had some great debates on the ''strain'' issue some years back.

Strain causes such a slight difference in Refractive Index of diamonds as to make a visible difference if one were to be examining a diamond on earth from the moon (with such a huge telescope, that would infact negate the effect anyway).

Sergey and Yuri weighed in with evidence to support this - so please read some of the old threads before we raise this debate again.
Well Garry, I''ve SEEN stones with strain visible WITHOUT crossed polars..
And my statement stands on technical fact, regardless of what you chose to believe.
Too much Sun in the land down under, me thinks..
 

Garry H (Cut Nut)

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Date: 12/20/2006 5:26:04 PM
Author: adamasgem

Date: 12/20/2006 5:12:38 PM
Author: Garry H (Cut Nut)


Date: 12/20/2006 4:05:54 PM
Author: adamasgem

2) Perfect physical symmetry MAY NOT show up as perfect optical symmetry because of strain

In a strain free stone, perfect physical symmetry = perfect optical symmetry
Marty we had some great debates on the ''strain'' issue some years back.

Strain causes such a slight difference in Refractive Index of diamonds as to make a visible difference if one were to be examining a diamond on earth from the moon (with such a huge telescope, that would infact negate the effect anyway).

Sergey and Yuri weighed in with evidence to support this - so please read some of the old threads before we raise this debate again.
Well Garry, I''ve SEEN stones with strain visible WITHOUT crossed polars..
And my statement stands on technical fact, regardless of what you chose to believe.
Too much Sun in the land down under, me thinks..
I know what you mean - often associated with strong graining and fluoro cluodiness - I knocked back a D SI1 strong blue (called Medium by HRD) that had no kick even though the cutting was very optically symmetrical. The price was great - but obviously the stone keeps getting knocked back.

But this is a seperate issue to the idea that strain results in differing symetry appearance becuase of variations in RI 9which is what I assume you mean?)

Weather has been mild here and there is little sun as it is blocked by smoke from bush fires (forest in your lanuage)
 

adamasgem

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Date: 12/20/2006 5:49:24 PM
Author: Garry H (Cut Nut)

Date: 12/20/2006 5:26:04 PM
Author: adamasgem


Date: 12/20/2006 5:12:38 PM
Author: Garry H (Cut Nut)



Date: 12/20/2006 4:05:54 PM
Author: adamasgem

2) Perfect physical symmetry MAY NOT show up as perfect optical symmetry because of strain

In a strain free stone, perfect physical symmetry = perfect optical symmetry
Marty we had some great debates on the ''strain'' issue some years back.

Strain causes such a slight difference in Refractive Index of diamonds as to make a visible difference if one were to be examining a diamond on earth from the moon (with such a huge telescope, that would infact negate the effect anyway).

Sergey and Yuri weighed in with evidence to support this - so please read some of the old threads before we raise this debate again.
Well Garry, I''ve SEEN stones with strain visible WITHOUT crossed polars..
And my statement stands on technical fact, regardless of what you chose to believe.
Too much Sun in the land down under, me thinks..
I know what you mean - often associated with strong graining and fluoro cluodiness -Also because of HPHT I knocked back a D SI1 strong blue (called Medium by HRD) that had no kick even though the cutting was very optically symmetrical. The price was great - but obviously the stone keeps getting knocked back.

But this is a seperate issue to the idea that strain results in differing symetry appearance becuase of variations in RI 9which is what I assume you mean?) Yup.. theoretically I am correct.

Weather has been mild here and there is little sun as it is blocked by smoke from bush fires (forest in your lanuage) Sounds like parts of California sometimes. Weather sucked generally in New Zealand two weeks ago, but there was no bush fires..
 

strmrdr

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Date: 12/20/2006 12:20:10 PM
Author: adamasgem

Date: 12/20/2006 11:57:47 AM
Author:strmrdr
Something that Iv been thinking about is virtual facet size vs viewing distance.
Peter talking about virtual facets in the vid and Garry''s discussion of shallow stones got me thinking about it.

For example are larger virtual facet sizes an advantage in the longer viewing distance when mounted in pendants and earrings.
I do know that a well cut asscher when moved can send out a huge flash of attention getting fire, larger than pretty much any other diamond Iv seen.

As distance increases the eyes ability to separate fine details rapidly falls off.

2nd part of the question would be: virtual facet size and fire, it seems like the stones with large virtual facets Asschers, EC and oec mostly return fire but are not the brightest stones around.
Do larger virtual facets decrease white light return and increase fire?

3rd part and if I had DC working I would look into it:
What has the greatest effect on virtual facet size in the standard RB cut?
lgf% is one.
Does high crowns with shallow pavilions increase them?
The greatest effects are due to the general lack of opticall symmetry and mis-alignments. I haveshown this in my fire performance photos..where you see broadflash fire, every real facet lighting up with one purer color, instead of smaller areas of color of muted colors
assume perfect optical symmetry what is the effect of larger virtual facets?
 

Garry H (Cut Nut)

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Date: 12/20/2006 5:59:24 PM
Author: adamasgem

Date: 12/20/2006 5:49:24 PM
Author: Garry H (Cut Nut)

But this is a seperate issue to the idea that strain results in differing symetry appearance becuase of variations in RI (which is what I assume you mean?) Yup.. theoretically I am correct.
Hooray, you have just discovered a learning opportunity Marty.

Do some searches and read the old threads.

Until then there is no point rehashing old information.
No more comments until then
 

adamasgem

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Date: 12/20/2006 6:05:53 PM
Author: strmrdr


Date: 12/20/2006 12:20:10 PM
Author: adamasgem


The greatest effects are due to the general lack of opticall symmetry and mis-alignments. I haveshown this in my fire performance photos..where you see broadflash fire, every real facet lighting up with one purer color, instead of smaller areas of color of muted colors
assume perfect optical symmetry what is the effect of larger virtual facets?
Storm.. later on today we'll have two large uploads showing the ASET virtual facet images versus tilt (look angle), courtesy of Peter Yantzer of AGS. Leonid has kindly uplaod the first of the two comparisons, the first one is at www.pricescope.com/uploads/p4075t53c345s50lg80-combine_lg.gif wwhich shows the ASET 30, 40 Fire and Reverse Fire Renderings (lighting acceptance zones).

While on vacation Peter said he would also try to generate the misaligned pavilion case, which would, in my opinion, tend to increase the number of virtual facets.

In the meantime, I guess I could comment, that the observability of virtual facets, will of course be a function of the lighting envirionment and the resultant contrast generated for the image.

I believe Fire Performance Images can best show the effects of virtual facets, as each virtual facet seems to light up a different color, as shown in this saturation enhanced photograph below. Logically, the larger the virtual facet, the higher the probability for one to "see" it, either via black/white contrast (scintilation) or by catching the fire.

Smaller virtual facets will not be able to be resolved as you move away from the stone, probably because of color mixing, the pinfire versus broadflash opal analogy.. either internally in the stone or externally to the retina (or camera lens) to create the composite color seen. If each point on the lens (human or camera) focuses the same color on a retina point projected from a point on the stone, you will "see" that pure color hue.

To me, it is a complex interaction of the envirionment (lighting), the geometrical optics of the stone, the internal absorption within the stone, and the viewer's position, pupil size (intensity adaptation) and retinal sensitivity, not easily explained.

Pictures are worth a thousand words.

The more uniform and diffuse the lighting envirionment (lack of contrast) the more the lack of contrast in the refracted (+reflected) projection from the stone. If the stone strongly internally absorbs a color (such as blue in cape series diamonds) than tat color will not be "seen" , except that portion reflected from the surface of the stone (glare).













20034002.gif
 

adamasgem

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Here are the links to the virtual facet ASET images versus tilt (5 degree increments) courtesy of Peter Yantzer of AGS Laboratory.
.
Thanks also to Leonid for uploading the large files...

The file naming conventions define the parameters..
Symmetrical..

Both have 53 Table size, 80% Lower Girdle facet length

Nominal Tolkowsky

40.75 pavilion angle 34.5 Crown
www.pricescope.com/uploads/p4075t53c345s50lg80-combine_lg.gif

40.4 pavilion angle 36.5 Crown Angle


www.pricescope.com/uploads/p404t53c365s50lg80-combined.gif

These ASET images show the regions where the virtual facet is collecting the light...

One has to realize that NO stone has "perfect" physical symmetry, nor can one "really" measure the stone, and that ANY small measurement error may propogate into a substantailly different rendering, ASET or phototreal, and by their vary nature, these analyses are qualitative...

EVEN physical devices, especially like a small Hearts and Arrows Viewer are limited, as relative size of the stone to the device (~1" diameter in the H&A case) alters the input ray coloration (image) and that two IDENTICALLY cut stones of different sizes will present different images..

The larger the device, the smaller the contrast (color) cutoffs and the less sensitive the visual presentation is versus stone size..

One can only do the "job" consistently by software, and even then the limitations of the scanners come into play..

One small note for the community is that while in Israel I visited Sarin, and they have made great improvements in their scanner recognition software with regard to being able to "accurately" scan the EightStar and NewLine class of stones, and I believe the software upgrades will be distributed shortly.. I will be discussing some minor issues with them, and will be interested to see comparisons of the scans among various vendors on the same stone (Helium/OGI/Sarin {in alphabetical order]). More on this in a new thread..



 

strmrdr

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Thank you Peter, Marty and Leonid!!!

I love images because its one of the ways I learn best.
Looking over the fire maps it sure is interesting and once Iv had some time to think about it will post comments and questions.
 

strmrdr

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Date: 12/21/2006 9:57:29 AM
Author: adamasgem

One small note for the community is that while in Israel I visited Sarin, and they have made great improvements in their scanner recognition software with regard to being able to 'accurately' scan the EightStar and NewLine class of stones, and I believe the software upgrades will be distributed shortly.. I will be discussing some minor issues with them, and will be interested to see comparisons of the scans among various vendors on the same stone (Helium/OGI/Sarin {in alphabetical order]). More on this in a new thread..

Way kewl I cant wait for Jon to get his hands on it and generate some helium and sarin DC models for the same stone!
Will be interesting to see if it helps with asschers also.
 

Rhino

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A peek to the future ...

Thanks for putting me onto this thread Marty. Here is a scan of the same stone, which happens to be an EightStar on the 3 scanners. All with the most current updates.

As Marty pointed out Sarin is releasing an update which is not yet distributed to improve modeling. I would add that OGI is as well and I''m expecting an updated scanner as well as updated software from them within the next week or two. These first screen shots are with the current OGI.

You''ll note in this first screenshot taken within the OGI software itself it''s difficulty resolving the upper half facets becuase their angles are so so close to the actual crown mains. Stones like this are the hardest for a scanner to detect however OGI has pointed out to me that their scanner does indeed *see* these facets but the model in the current software isn''t showing them. More on this in the next graphic.

eightstarmodel01.jpg
 

Rhino

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Interestingly this file is generated from the same scan except as observed via OGI''s Web Viewer software. Each upper half facet is resolved and each upper half angle can easily be read by simply clicking on the facet. To my knowledge these software changes will be reflected in the update that''s on its way.

Marty, look at the meet point faceting as well.

The OGI generates .stl files also and when I attempted an import into DiamCalc, for some reason it wouldn''t let me import the file. I was able to open the .stl file with a program Pete had turned me onto called "Solid View" and the model appeared as it does in the first graphic I posted above.

When I saw the model here generated by the OGI and if this is reflected in the new updates coming down the pike, I thought this was an excellent improvement and I look forward to getting their updated scanner/software on this.

Sarin next...

OGINEW8STAR.gif
 

Rhino

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Here a Sarin on the same stone. It''ll be interesting to see the updates on this and if they improve.

8starsarintweak.gif
 

Rhino

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Here''s a gem advisor file (small version) as generated from a Helium scan of the same stone. This is one reason (amongst many others) why Helium is king IMO when it comes to the details given in a diamond report. If you have DiamCalc you can drag and drop this file into DiamCalc and see the wire mesh of it.
 

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Serg

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re:"'Marty, look at the meet point faceting as well.



The OGI generates .stl files also and when I attempted an import into DiamCalc, for some reason it wouldn't let me import the file. I was able to open the .stl file with a program Pete had turned me onto called "Solid View" and the model appeared as it does in the first graphic I posted above.



When I saw the model here generated by the OGI and if this is reflected in the new updates coming down the pike, I thought this was an excellent improvement and I look forward to getting their updated scanner/software on this"'

Rhino,

please scan diamond with just good meet points faceting ( +-20 microns) and publish same OGI image.
There is easy to receive model with perfect meet points faceting( simple rounded). One algorithm for excellent and good symmetry, other for bad symmetry. But all good will come to excellent

 

Rhino

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Will do Serg. As soon as I find time tomorrow I''ll try and post it for a comparison. I think I know what you''re getting at.

Best regards,
 

adamasgem

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Date: 12/21/2006 5:33:57 PM
Author: Garry H (Cut Nut)
i am flat out - but will come back when have time

intersting
is peter going to do one with twisted facet alignment? He said he would try to create one..

This is the right thing to do for +10ct round stones I I think that might be too much of a generality Garry, but I know what you are thinking and might tend to agree with you, but I don''t know the tradeoffs between extra virtual facets due to alignment and a different facet arrangement to get a different "look" (balance between broadflash fire and scintillation).

I guess the question you are getting at there, is what is the optimum size of the mirrors on a disco ball versus the diameter of the ball??


Have you seen the American Star?


 

adamasgem

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Date: 12/21/2006 8:16:33 PM
Author: Rhino
Interestingly this file is generated from the same scan except as observed via OGI''s Web Viewer software. Each upper half facet is resolved and each upper half angle can easily be read by simply clicking on the facet. To my knowledge these software changes will be reflected in the update that''s on its way.

Marty, look at the meet point faceting as well.

The OGI generates .stl files also and when I attempted an import into DiamCalc, for some reason it wouldn''t let me import the file. I was able to open the .stl file with a program Pete had turned me onto called ''Solid View'' and the model appeared as it does in the first graphic I posted above.

When I saw the model here generated by the OGI and if this is reflected in the new updates coming down the pike, I thought this was an excellent improvement and I look forward to getting their updated scanner/software on this.

Sarin next...
Would you email me the stl file..
 

Rhino

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Hey Serg,

Here''s an example. This is the OGI screen shot taken from the Web Viewer software. Gem file next.

br91symm.jpg
 

Rhino

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Here''s the GA file generated from Helium. I''ve inspected this stone carefully comparing to the Helium model. It''s spot on regarding the meet points, truncated facets, etc.
 

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