Girdle Treatments: Cheated Girdles, Tweaked Girdles, Digging & Painting

[Garry H (Cut Nut)]

Ignore this post and attachment- there is a problem with these files; Vladimir will fix it for the next full release of DiamCalc 2.4

 

[Garry H (Cut Nut)]

This stone is deeply dug out - if you open this Gem adviser file you will see what I mean.
It has Tolkowsky proportions - but leaks like a seive.
Turn the stone and look at its girdle - and look at the DiamCalc light return scores and contrast.

You will see the most important light return - stereo moving thru 30 degrees - is down to .88 - 12% below - but the contrast is up to 1.03 because the leakage bumps it up.

(For DiamCalc 2.4Beta users - Dear Garry, Thank you for informing us about this issue.

It seems that the current release of GemAdviser is not able to read properly Brilliant cuts with extra parameters that were introduced in the beta of DiamCalc. This issue will be fixed and two programs will be synchronized when the full DiamCalc2.4 is released.

Though... There is a workaround method. After you created the necessary cut in DiamCalc export it into GemCad ASCII or DXF file. (Menu Cut > Export cut). Then import it back. Then export the model to GEM file as usual. Hope it helps.
Vladimir)

 

[JohnQuixote]

For those keeping track at home: Garry''s "Dug Out Deeply from DXF"

Main crown angle is 34.5

 

[JohnQuixote]

The UGs are all 48.84 degrees. This is a variance of 14.34 degrees, or "whopping!"

Note: This cheated diamond was created virtually in DC, so it's uniform all the way around - thus the 48.84 can be used as an average. The tweaked examples used on page 1 were scans of actual diamonds, so the avg was used (the difs can be found on the Sarin screen shots on page 1).

 

[JohnQuixote]

DiamCalc ideal-scope and ASET simulations

 

[JohnQuixote]

DiamCalc estimation

Date: 11/21/2005 2:08:42 AM
Author: Garry H (Cut Nut)

You will see the most important light return - stereo moving thru 30 degrees - is down to .88 - 12% below - but the contrast is up to 1.03 because the leakage bumps it up.

 

[JohnQuixote]

And... DC pavilion patterning (of course, in this DC-created diamond the facets will be perfectly uniform)

 

[Rhino]

Hi John,

A poster recently quoted this thread which reminded me of it and thought I might share some of my finds with regards to what you have posted. In the example you gave, specifically the one on digging is at fault so I thought I''d just clarify. We have clients who consult the Gem Advisor files and the images they produce and we''ve been getting some clients who were confused by your example which is another reason I''d like to clarify.

In the digging example (btw thank you kindly for the GA file) the stone you provide as the example I find actually isn''t dug out at all. Sergey and Garry can correct me if I''m wrong of course but on dug out stones the girdle is always thicker at the mains and not the halves. In your dug out example the girdle is actually thicker at the halves and not the mains (which is in fact evidence of just the opposite ... painting).

This graphic below shows an example of the profiles of both a painted and dug out stone which would not make GIA Ex grade.

 

[Rhino]

This is the profile of the example you had given which was confusing some folk.

The example Garry provided is an example of some extreme digging. We see this alot on common commercial stuff. Please dont'' take my criticism in the wrong spirit John. Just trying to help.

Kind regards,

 

[Rhino]

Here are the GA files for your inspection. Both are precision cut goodies but suffer in the optics department due to the painting/digging. This is of the dug out stone.

 

[Rhino]

Here''s of the painted (similar to your example). BTW I like how you compiled the data John. Good job.

 

[JohnQuixote]

Date: 5/19/2006 5:10:27 PM
Author: Rhino

This is the profile of the example you had given which was confusing some folk.

The example Garry provided is an example of some extreme digging. We see this alot on common commercial stuff. Please dont' take my criticism in the wrong spirit John. Just trying to help.

Kind regards,

Rhino, I have no problem with peer review. After seeing the April GIA diagrams your example is a good one. I can explain why mine from last November confused you:

To a diamond cutter, when you ‘dig’ the angle is made steeper. ‘Painting on’ makes the angle more flat. Below are illustrations showing that in both our examples this is the case, as was discussed on page 1. Look at the orange lines and you’ll see what I mean. Sometimes terms used upstream, where cutters say one thing, differ from downstream (you may recall the ‘cheated girdle' vs. 'cheating screw' discussion). Being downstream, and not being a cutter, there is no reason you would have known this.

I have no argument with the GIA definition and I think your illustration is more appropriate for the thread. I’ll find an example with a girdle profile thicker at the bezels and switch it out for the one used earlier. I appreciate you bringing it up.

 

[JohnQuixote]

I took your stones and rotated the illustrations so the halves are straight-on. Now you can see the similarities to the prior example in how they were ‘taken’ or run on the polishing wheel (compare the orange lines to those above).

 

[JohnQuixote]

This is an unrealistic example. The orange lines show very steep (dig) vs. very flat (paint) taken to extremes.

 

[JohnQuixote]

Date: 5/19/2006 5:24:06 PM
Author: Rhino

Here's of the painted (similar to your example). BTW I like how you compiled the data John. Good job.

The additions are good. Thank you, Rhino.

Back when this thread was posted it was to illustrate techniques of cutters, using simple examples to help average people understand steep vs. flat. We were not using girdle profiles to identify the stone, just showing how a diamond cutter digs and paints (those polish diagrams are simplified as well).

I recall you contacting me and Garry some months ago saying ‘friends at GIA’ emailed you about this thread but you could not identify anything specific. When I asked you to elaborate you didn’t want to reveal their identities and I heard nothing further until reading this. NOW I understand why the question mark appeared over your head.

I’ll get an example conforming to the GIA lexicon posted on page 1 as time permits. Thanks for the alert.

 

[He Scores]

John and Rhino...I doo hope to get to talk to you in Las Vegas.

I'd just like to add to this fine discussion. No criticism is intended but just to open up some minds to the art of diamond cutting.

Painting and digging are not products of just a girdle facets angle. The STRAIGHTNESS of that particular facet is just as important when the cutter makes an adjustment to the facet. In fact, at a certain point in it's size a brilliandeering facet cannot be 'dug' simply by increasing the angle without dire consequences like missing the midpoint in the main facet. It's interesting that many performance models assume that facets are straight with each other when trying to determine the direction of light (Ray Tracing) just as one angle of main is used from the averages of all. Major differences can occur in all the cases.

The face up view that has been marketed heavily by some manufactures of "premium" cut stones should not be the end all for what a diamond looks like. While pasting top halves may allow for less light leakage when viewed in one particular position, it cuts down on the definition between the mains and themselves(like John appropriately pointed out) and this makes for a lack of what I call "scintillation" or the reflection of light off the facet surfaces (or whatever the hot topic name for it is in the labs). In addition to that, to some there is beauty in a straight and even girdle all around rather than thinner or thicker at the point under the halves. On the other hand, "digging" even slightly reduces the angle between each half in a set with a similar reduction of facet reflection.

The Tolkowsky Model is a compromise between all of the above factors, including the face up appearance and that's why I think it will always have a larger market share than just the performance stones.

Also John, just for your edification, the direction in which a facet is polished (read aligned with the wheel) has no primary and direct relationship with the angle the facet is made on. This alignment is dictated by the granular structure of the diamond and MAY however, be influenced by angle but not in every case.

This is pretty ecclisiastical, so I'll stop. However, I think all you "cut nuts" should take time out and sit at the wheel with a cutter and learn how to cut. It can only add to your already broad understanding of workmanship.


Bill Bray
Diamond Cutter

 

[JohnQuixote]

Hi Bill,

Back in November Brian Gavin warned me that a technical 'cutter shoe' could drop in this thread.

That's the danger of simplifying the extremely complex. When questions were raised on the forums the info and diagrams here went up with the intent of helping consumers with a mental picture.

Date: 5/22/2006 4:38:05 PM
Author: He Scores

Painting and digging are not products of just a girdle facets angle. The STRAIGHTNESS of that particular facet is just as important when the cutter makes an adjustment to the facet. In fact, at a certain point in it's size a brilliandeering facet cannot be 'dug' simply by increasing the angle without dire consequences like missing the midpoint in the main facet. It's interesting that many performance models assume that facets are straight with each other when trying to determine the direction of light (Ray Tracing) just as one angle of main is used from the averages of all. Major differences can occur in all the cases.

One challenge in trying to represent this is that the rules are limitless in reality, but more limiting and subject to nature's whims at the wheel. It's not possible with a real diamond to adjust a wire frame thicker or thinner like anyone can do in software. On the wheel you can only adjust angles (steep or flat) or cheat (left to right). Even knowing this, most people don't understand the way a facet runs on the wheel.

You said:

Also John, just for your edification, the direction in which a facet is polished (read aligned with the wheel) has no primary and direct relationship with the angle the facet is made on. This alignment is dictated by the granular structure of the diamond and MAY however, be influenced by angle but not in every case.

Understood. I previously said:

Date: 5/21/2006 8:35:45 PM
Author: JohnQuixote

Back when this thread was posted it was to illustrate techniques of cutters, using simple examples to help average people understand steep vs. flat. We were not using girdle profiles to identify the stone, just showing how a diamond cutter digs and paints (those polish diagrams are simplified as well).

The diagrams were created to give understanding to the average person: For instance, in order for the diamond to be polished we gave an example of painting from star to girdle...In reality it may still be taken from the girdle side, but because the angle is so flat and so little material is taken from the girdle, the simplified drawing was to demonstrate the principal.

This is pretty ecclisiastical, so I'll stop. However, I think all you 'cut nuts' should take time out and sit at the wheel with a cutter and learn how to cut. It can only add to your already broad understanding of workmanship.

Bill Bray
Diamond Cutter

I will give you hallelujah.

Actually, I work with a cutter every day, but regrettably he won't trust me with rough yet.

Actually, we do intend for me to sit at the wheel with him sometime. I don't know if you have met Brian Gavin, my boss: He is a 5th generation cutter - you know, played with rough like some kids play with marbles... He began producing 'A Cut Above' diamonds with his first company, Alpha Creations, in Houston back in the late 90s, buying rough on the open market. Now our production has moved to Antwerp, where he is a consultant for the factory.

Thanks for the acknowledgment and the input. Any further comments you have are welcome. I'll be in Vegas Thurs-Tues.

 

[JohnQuixote]

Date: 5/22/2006 4:38:05 PM
Author: He Scores

The face up view that has been marketed heavily by some manufactures of 'premium' cut stones should not be the end all for what a diamond looks like. While pasting top halves may allow for less light leakage when viewed in one particular position, it cuts down on the definition between the mains and themselves(like John appropriately pointed out) and this makes for a lack of what I call 'scintillation' or the reflection of light off the facet surfaces (or whatever the hot topic name for it is in the labs). In addition to that, to some there is beauty in a straight and even girdle all around rather than thinner or thicker at the point under the halves. On the other hand, 'digging' even slightly reduces the angle between each half in a set with a similar reduction of facet reflection.

The Tolkowsky Model is a compromise between all of the above factors, including the face up appearance and that's why I think it will always have a larger market share than just the performance stones.

Painting and performance qualities: I believe this is impacted by distance to the diamond as well as the optical symmetry. Within robust proportions sets painting can maximize beauty. It may or may not even be visually distinguishable from non-painting; as must be reiterated, it depends on how much. It is possible to over-paint, and it’s possible to do this with traditional brillianteering too. Too much painting results in less definition of the bezel facets. The opposite is going too far in the traditional manner (digging), which can result in performance issues or even a knife-edge girdle. In either situation, when quality control is present, the diamond can be beautiful. It all boils down to the quality and care of the manufacturer handling the stone.

Premium painted diamonds I am experienced with (examples with great optical symmetry) have more brightness & less dispersion the closer you get, but at farther distances you see larger flashes of dispersion/broad-flash fire. Close up contrast - again, with good OS - is wonderful. It is a hot topic at AGS. Experts are finding that it may be more appropriate to say the quality of scintillation influences your ability to see fire (or not). If the ‘virtual’ facets - reflections and double reflections, etc. - are too small, you may see more white sparkle and not fire. This makes sense. The opposite would be old European cuts with large facets where you will see abundant fire and not so much white scintillation.

Relative to all of this, the optical symmetry theories being discussed are fantastic, and right up my alley. Marty Haske is thinking along the same lines here (this is opinion, not strict science): If you get a ray of light in and out of a diamond faster it doesn’t lose energy and the dispersion won’t mix with the fresnel (secondary) reflections so much. This may result in purer spectral hues and more energy leaving the diamond. It makes sense when you consider the notable ability to see broad-flash fire from far away in diamonds with certain configurations plus high levels of optical symmetry. The longer the ray stays inside the stone the more the colors mix and more energy is lost so you see less pure hues. This would explain why dispersion in diamonds with poor optical symmetry sometimes takes on a muddy look. It meshes with what some notable cutters and scientists have been musing for some time.

 

[He Scores]

Oh ...and John.

Visit me and I''ll have you cutting on a diamond before your first cup of coffee gets cold.

It won''t score very high on BrayScore but you''ll be able to say you did it.


Bill