Yaw Angst

[michaelgem]

Date: 9/18/2005 7:42:14 AM
Author: beryl

Date: 9/18/2005 4:52:33 AM
Author: Garry H (Cut Nut)

From my knowledge of ETAS, this software approach is more predictive and more valuable than direct observation techniques because the direct techniques do not yet seem to be capable of showing that they can account for all the factors relevant to human perception.

Garry:
. The above is well-written; please tell me what ETAS means. Bruce Harding

ETAS (effective total angular size) is similar to the reflection and refraction pattern projected on a sphere from a beam of light along the line of sight from the observer to the diamond. Sergey calls it the part of space visible through the diamond, because through reverse ray tracing we see that these are the locations that are the source of the light visible in the diamond.

GIA generates a similar pattern and uses it in their DCLR metric.

AGS calls it their Angular Spectrum from which they get the name for their ASET tool (Angular Spectrum Evaluation Tool)

The Gemprint is a monochromatic version projected on a plane rather than a sphere. Makes a nice "fingerprint" for a diamond, as it is unique to each diamond.

I look upon it as the "constellation" of points in the space surrounding the diamond that are being reflected and refracted to your eye from within and without the diamond.

Michael Cowing

PS Note that my explanations here are kept simple, so as not to loose the basic concept in added complexity. Sergey or Garry may wish to elaborate.

 

[Serg]

Thanks, Michael.

I will add a little.

ETAS depends from size virtual facets.

See http://www.gemology.ru/cut/english/conference_posters/4.htm

GIA and AGS similar metrics do not depends from size virtual facets.

ETAS could be static, dinamic, mono, stereo, positive and negative

 

[Rhino]

...

 

[RockDoc]

I am reading this thread with interest watching the conclusions of many experts.


My take on this sort of parallels David''s position, but with a further item of concern.


Let''s for the moment say that the particpants of this thread come to a uniform and universal acceptance of what should or what should not be relevant.


Is this super hair splitting going to really serve as very helpful and informatiive? Are diamond cutters going to avoid "cheating" so that the yaw is all uniform? I would estimate that probably 95% of the folks in the business, don''t comprehend what really well formed H&A images mean or are, much less having the skill to adjust to meet the currently considered "standards" not to mention the willingness to wilfully be blind to the whole situation.

A standard is only a standard if it is practiced. Because of the individual characteristics of the material, its type, the size ( weight ), shape of the uncut material, and its internal structure could make coming to this perfect of an analysis, virtually impossible.

I do however, enjoy what all of you are sharing, and certainly curious and very interested in how the results will be interpreted into the current grading systems.

Further, since it seems that light return is still being calculated, I do have some concerns with the metrics used, as I believe that many other factors need to be addressed than already are.

I am also "super" curious as to the accuracy of what the scanners see. The industry seems to accept that this is "beyond the shadow of a doubt" correct. The published " variances / tolerances" are disclosed but I ponder as we get more in a hair splitting "contest" what the results of these studies will uncover, and will it really serve the interest of the buyer and members of the trade.

Rockdoc

 

[Rhino]

Hi Beryl,

While I am writing my letter on "The Journey to Azimuth" I wanted to respond to your answer.

Thank you for posting this answer but let me share with you my thoughts about what you wrote and how it can be confusing in the minds of some (particularly me).

My question, which I tried to keep as simple as possible ...

quote of Rhino (above):
. 'Question: When this effect of yaw is done on the diamond are the adjoining halves *always* twisted in opposite orientations? Ie. the one on the right is (+) while the other is (-). Is this always the result?'

As I read your responses to this Bruce in the following two posts your answer switches from no to yes to yes. Follow along with me...

First you conclude...

. As indicated above, there are 'infinite fixes' and this is just one. It is not necessary to twist halves 'A' and 'B' in opposite directions but if you look back to Fig.3 of that thread (see next post), you can see, by the phantom outline of the ideal facet, that we must do this to bring the tip of the main back to its 'proper position' on the girdle circle (equal-width scallops on both sides).

It is these answers Bruce that throw me for a loop. First you say "no, it is not necessary to twist them in opposite directions" then in the next breath say "yes, this must be done to bring the main back to its proper position". Since you had concluded with a "yes" I would take it to mean you meant "yes" as your final answer especially when I consider your next post where you state...

". Note that the steeper cutting has widened the lower end of the main. To bring it back to the point of the ideal tip (phantom line) it is necessary to twist both halves toward the main. Other fixes are possible but would not bring the tip back to this point."

So within two posts you state

No: It is NOT necessary. Then....
Yes: It must be done ... then...
Yes: It IS necessary ....

I am making every effort not to misconstrue your words and I don't want to arrive at a faulty conclusion cause if I think you said "yes" I don't want you to point out where you said "It is not necessary..." And if I construe your answer as "no" I don't want you to point to the places you said yes.

Can you understand how simple folk like me ... (who btw LOVES the KISS method) can be confused by these answers?

For sake of simplicity and clarity Bruce I am going to reword this question using the KISS method so there is NO ambiguity. I believe you are here for the same reasons I am. To bring clarity and light. Not heat and confusion.

Question: When this effect of yaw is done on the diamond are the adjoining halves *always* twisted in opposite orientations? Ie. the one on the right is (+) while the other is (-). Is this always the result?'

a. Yes.
b. No.
c. I don't know.

KISS: Choose a. b. or c.

Peace and thanks,

 

[RockDoc]

Hi Beryl et al.


I have a question.....

It appears to me that most if not all cutters when cuting the pavilion of a diamond cut the 8 main facets and then bring in the halves.


Why not do the opposite? Cut the 16 lower girdles first, then incising the mains ( just 8 ) would seem a lot easier to center and be more exacting with the LG length ( or height as some call it) ?


I''ve found this much easier when cutting colored stones. I admit I''ve never cut a diamond, and perhaps there are some issues with dealing with the direction of polish that diamonds require, that colored stones don''t have.

Rockdoc

 

[Rhino]

Hey guys,

While I appreciate this discussion and John’s attempt to bring order, I feel if I do not share a little of what it is we are discovering here, things may go awry and my goal here is not to generate anymore heat, but to shed light.

The subject of azimuth and yaw has drawn much attention as a result of these threads and while certain claims have been made on my end, I have not yet presented any results of the research & studies I am personally conducting as I had planned on publishing the generals of this in our upcoming article on the reflectors and what the differences are between them. So to erase any doubts or misconceptions I feel it is imperative to share the perspective from which I have been approaching this. I realize, through the illustrations and teachings of Bruce, Brian and Paul that we have been approaching this from an entirely different angle and because I have not been approaching this from “the cutters angle” I can understand why any of you, my peers, may perceive my claims as hype. I understand your perspectives now though admittedly it was tough to grasp at first.

This lil letter could properly be termed…

‘Rhino’s Journey to Azimuth”

I think you may find this interesting since I am unfamiliar with the everyday language of cutters and like any other subject I like to keep it simple and explicable in layman’s terminology. I will attempt to avoid what Mike Cowing is referring to as “rocket speak”. Terms like “cheater screw”, “azimuth angles”, “azimuth shift”, “yaw” and whatever else everyone reading didn’t understand … I feel your “angst”.

So I’d like to share a brief history which has led me to this point.

Back in 2001, I had, of necessity constructed a lens for photographic purposes to both view and photograph phenomena I was observing through the FireScope ™. Since I was making this from scratch and from different materials I thought to myself “What is it about the FireScope™ that I would change?” After determining the changes I proceeded to construct our DiamXray/LightScope technology to help me better understand the phenomena I was observing in another completely unrelated yet very much related technology, which at first seemed totally at odds with FireScope technology. That was the BrillianceScope.

After working with our new invention for some time I immediately began to make correlations with the optical designs I was observing through LightScope and how it impacted BrillianceScope results, but even more importantly … what correlated with the eyes of my clients since the goal here (and that of any research science) should be to better serve our fellow man. This was no secret here and when I was discovering and noting those correlations I had published the results of my findings in our present tutorial on “The FireScope/IdealScope” which show these correlations between the 2 technologies developed by firms that did not necessarily see eye to eye. Certain members of this forum have literally watched the evolution of my learning process with these technologies so none of this is secret information. You can ask Garry, Leonid, Mike Cowing and other researchers who have been following my work over the course of the time that I have been participating on the forums.

One of the notable differences I had discovered with our new invention was that I was able to distinguish sharp contrast differences between reflections that were happening on the pavilion and since that time I had been noting how they affect results on various other technologies we use in our exam BUT MORE IMPORTANTLY the face up appearance in various light conditions. What Mike Cowing properly refers to as “direct assessment”.

You see… the focus of my studies … the angle of perception from which I am and have always approached the study of diamonds has been almost exclusively through the crown. Why the crown? To me the reasons are obvious.

I can understand the perspective of analyzing the pavilion through an H&A viewer even more now and to a greater extent but this has not been the venue that God has seen fit to guide me in my research. Before I proceed John posed a couple of questions which I’d like to share my answers on …

(1) Can we have a discourse of fine make cut/craftsmanship and arrive at a definition of what is observed as yaw?

Yes and I am eager to learn more. This is why I am asking the questions I am about this phenomena and how they relate to the numerical/geometric measurements noted in Bruce’s graphic. No disagreement here Sir John. We’re on the same page.

(2) Can we agree that the simplest way to observe pavilion facet construction details (NOT performance) is with a H&A viewer?

At this point in time my answer would be a definite yes. I am very young in my research on azimuth and yaw and its impact on the optical signature so if you were to ask me this question a year from now my answer might change or it might not.

(3) Knowing we can see it through a H&A viewer - Which of the scanning machines, if any, pick it up?

At this point in time my conviction is that Helium does it best however I am told that Sarin is working on this to a greater extent and we have seen improvements in the models due to tweaks we have incorporated into the software. As stated earlier by me in this thread, answering the last question demonstrates precisely what each of these scanners see. That is why I feel compelled to share my journey here. My prayer is the conclusion of this letter will better help in this understanding of “what a scanner sees” and bring peace to the “angst” this has conjured up on the hearts of some here, including me.

(4) FINALLY (save it for last) - What potential does yaw have to influence light performance?

We are getting there my friend. 

Ok… back to the journey.

As I think back to the infancy of observing differences in optical signatures a very vivid moment stands out in my mind and is, I believe the very first time I was observing azimuth shift in an ideal cut resulting in leakage. Mike C … you were standing beside me too. It was at the EightStar Symposium you and I had attended when I was an 8* dealer and when you were under their employ. Richard was showing us a stone that did not qualify for being an 8* and asked us if we could identify *why*. I immediately noted the phenomena and if you remember correctly Mike I think both you and I photographed it under the FireScope. Do you remember that?
It was then the question formed in my mind… How can a diamond with ideal proportions (ideal slope angles) have this leakage (thus impacting light performance) within a round brilliant cut?!?! I recall Richard saying “It is because the facet was twisted” and that was the end of it but I never forgot.

I have studied in great length how the minor facets impacted the optical signature and the changes that occurred in that signature and how it impacted the metrics of brilliance, fire and scintillation (I published the results of this study in our tutorial on the minor facets) but there was still this other facet of my study I just could not understand and thought perhaps it had to do with the *twist* reported on a Sarin which it turns out not to be.

You see … as a retail jeweler who has taken the GIA courses on diamond grading/advanced diamond grading and reading many other materials, the subject of azimuth angles is rarely if ever discussed. Few retail jewelers and many within the trade just don’t know. So when I had 2 diamonds with identical or virtually identical proportions regarding slope angles yet were getting different (sometimes drastic) optical results I could point out the differences in the optical signature but I did not know what was causing those differences. I refer to the graphic below.

 

[Rhino]

Note the contrast between the depths of the reds under the tables in these 2 examples. This correlates directly to the *intensity* at which light is exiting the diamond. Note the crown angles are identical and within .01 of a degree. There is a difference in slope angles on the pavilion. The slightly steeper slope angles of the stone on the right cause those dark red spikes to not extend as further down the pavilion as the stone on the left.

That is a change in the optical signature due to slope angles and the north/south orientation. Garry and I are aware that some stones, when hitting that critical 41 degree angle (can cause more leakage).

That is not the point of this study however.

Note the lower girdle adjacent to the main at the 1:30 position. That reflection is altered causing light leakage within the diamond and alters the optical signature as observed in DiamXray. The opposite lower halves are altered to some degree as well to a more minor extent but that (at 1:30) is the most obvious altercation and reminds me back to what me and Mike were observing to a lesser extent 5 years ago through the FireScope™.

 

[Rhino]

A twist has occurred in the geometric plane which is reflected in the optical signature.
How do I know this?

Enter Helium.

Here are the azimuth deviations from ideal on the diamonds as *seen* by Helium.

(By the way I have generated DiamCalc files on each of these diamonds through the Helium software which allows you to print out full reports including azimuth angles and how far they deviate from ideal as well as slope angles and every other frog hair you can imagine on each of these stones. The DiamCalc files are yours for the asking and at the completion of this short article I will be forwarding to Garry, Sergey, Brian, & John these files. I have these 4 emails on hand but anyone else … Mike Cowing, Bruce Harding, Strmrdr, Valeria, Belle … if you would like to study the results of my findings these files show all the details and then some which you can compare to actual photography through DiamXray/LightScope for comparison. We’re not done yet though.

Note on the 1.33ct F VS2 (stone on the right) that one lower half deviates from ideal a full 1.27 degrees (not even to the extreme Bruce used in his graphic on yaw which deviate around 4-5 degrees).

 

[Rhino]

Here is azimuth deviation from ideal on the stone with the altered signature. Note the lower half that deviates 1.27 degrees in red.

 

[Rhino]

Is this lower half the offending facet I am observing in the face up view through LS? How do I know for sure? Quite simple actually. Load the model into DiamCalc and click on the facets. Due to the lens construction, lighting environment and tireless man hours we have duplicated what is now the default view in DiamCalc.

Compare.

Are they exactly identical? No. Which picture takes preference to the actual optics? The photo of the actual diamond of course.

 

[Rhino]

What does Helium see?
What does Sarin see?
What does OGI see?
What does any non contact measuring device see?

I can answer these questions in profound detail by simply comparing the models generated by each scanner and comparing those results to the actual photograph of the stone taken by duplicating the exact (or dam close) environment reflected in the DiamCalc lighting environment.

Want to know if Helium sees shift in slope angles to the nth degree? Identify it through the pavilion, send it here. We’ll photograph the optical signature and *if* the results can be observed through the crown we’ll know beyond a shadow of a doubt if Helium can see it. At this point and in this illustration I have used a diamond with azimuth shift in a lower half facet which was notably different than the others. An easy learning example. I have been extremely busy as of late so my research in this study is young and I have a long way to go but I believe I am on the right track. 

Next I will seek out a stone that has the characteristics John pointed out in the original yaw thread and post the results as time allows. According to John’s, Brian’s and Bruce’s posts it appears when yaw occurs there are 3 facets that shift in azimuth. If I can identify one (and even tell you its orientation (+) or (-), I feel confident I can identify three … through the crown.

Another question I sought answers to which were formed in my mind was …

To what extent is light reduced on the offending (twisted) facet? Here is some interesting stuff I did with DiamCalc.

• Load the 1.33ct F VS2 into DiamCalc.
• Put the setting on “Draft + Double Reflection”
• Turn on “Single Ray Trace”
• Take the beam of light and focus it on the offending reflection.
• Note the output.
• Take that same beam of light and focus it on a non-offending facet (with minimal azimuth deviation from ideal).
• Note the output.

The following graphics show this step by step procedure and the results.

Am I onto something? I refer to you, my peers.

 

[Rhino]

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[Rhino]

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[Rhino]

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[Rhino]

...

 

[Rhino]

...

 

[Rhino]

At earliest convenience I''ll address some of the other points raised by Dave Atlas, Mike C, Rock and others. Anyone who would like the DiamCalc files generated from the Helium software can pm me and check off the email option and I''ll forward the 2 examples used in this study. I am interested to hear your input.

Warm regards,
Jonathan

 

[aljdewey]

GEOX.

 

[RockDoc]

Rhino.

Interesting results on the two stone ray traces you posted. In looking at these two, I am wonder why the "shift" from the spectral colors on the 46% ray break at the facet surface, and why the change from the beam in the second result break into the spectral colors away from the surface.


It would also be interesting to see the Sarin MFG report showing the twist data, and Sarin''s wire frame deviations, as opposed to the Helium report as well as the OGI reports.


It would be interesting to also see the meet points generated by each scannerfor both the pavilion and the crowns. .


Also is you have an eightstar what each different scanner "sees" with one of those stones. It appears that sometimes the Sarin may sometimes have difficulty in accurately reading the break faceting, and wonder if the Helium recognizes and images this situation properly.

Rockdoc

 

[Rhino]

Also guys...

As of late I have been really trying to be more sensitive on my delivery. I apologize if at any point I come off sounding as if we were not face to face where you could see facial expressions etc and the feelings/expressions in my heart. I am excited to share the discoveries we are making and realize my tone may not have
come off good so if not I mean no offense.

Peace,
Jonathan

 

[Midnight]

Jonathan,

Can you please post the H&A photo displaying the offending facet/"twist"/"yaw" to correlate with the Lightscope of your example.

 

[Rhino]

Here it is Midnight.

 

[Rhino]

Here is arrows. I just tried to upload the GemAdvisor file but the Gem Advisor file generated by Helium is too large to post on this forum as its file size is greater than 300kb. A Scan from the Sarin and resultant Gem Advisor is much smaller and can upload to the forum.

Perhaps we should test the same stone on the Sarin and see what the Sarin sees?

 

[Midnight]

Jonathan,

Thanks for the generated H&A pics...but John and Brian might want to see the "real" H&A photos

to be scientifically consistent for comparison purposes. Do you still have the original H&A photo file on this diamond to post? I only suggest to help make your presentation more complete.

 

[Garry H (Cut Nut)]

Roc and Rhino - this is the leaky stone

 

[Garry H (Cut Nut)]

this is the same stone rotated 45 degrees.
Now you can better compare the 2 ray traces.
(Rhino sent me the dmc file)
(I also set the reflections to 9 and the minimal intensity to 0% - these controls are under Options - toptool bar > Advanced > Ray tracing, then the left side of the dialogue box)

Hopew this helps

 

[Rhino]

Date: 9/17/2005 7:30:26 AM
Author: oldminer
Rhino;

I know you are pursuing the quest for knowledge. This is commendable. However, think of the consequences to marketing if one is to separate quality of cut well beyond what people can visually appreciate in any way. I''m not saying that perfecting ways of detecting cutting perfection are at all bad, but can you imagine consumers belieiving they want optically pure diamonds for no other reason than for technical reasons?

Diamonda re a natural product and cut by people. They will have certain characteristics due to their initial cost and difficulty in cutting them which make each one what some might call a small work of art. Will yaw and twist be for cutting development? That sounds like a positive step.
If it enters the world of diamond grading, it may be suggested that it is beyond the realm of practical needs.

I find these threads of interest and mind expanding, but is anyone saying this is consumer oriented? I would hope this is cutter directed.

Hi Dave,

Thanks for your input. These aspects are really not things that would be noticeable to the naked eye Dave, particularly in the example given. That stone is no less beautiful because of one azimuth twist on a lower half, however we have learned from this example that one faceted twisted beyond 1 degree (and less than 1.5) does impact optical symmetry by making one heart inconsistent with the rest. Optical symmetry purists take note of things like this.

I guess one question that begs an answer is ... how much of this stuff has to be present before it begins impacting face up appearance? How many facets must be *twisted* or how much "yaw" must take effect before impacting face up to the layman? 1? 2? 10? These are questions we will try to seek the answers to as we continue our study here but I would say up front, slope will impact face up appearance more dramatically before azimuth will.

The reason this is of interest to me (correllating numbers to optics) is because many of the folks who come here come here with what? Numbers. The more numbers, the easier it is to assess how this stone may appear in various lighting conditions and the person coming to these forums are better served from an informational standpoint. IMO that reflects good on PriceScope. The more educated we all become on the subject the better people are served which is why I really do enjoy the input of all here. In GIA''s cut grading system, even though they are rounding I am happy to see them take into account more of these numbers (particularly lower half and star lengths). Even if a person does not agree with all the elements of the GIA Cut System I think it is great that they will be including that data on their reports and any expert here can, with those additional numbers share their professional opinion with more confidence regarding their experience with that type of stone.

I guess I think along these terms a little because of the industry we are in and the critical details that go into seperating monetary values between VVS1, VVS2 etc. D-E, etc. I too would consider these splitting a frogs hair but when you think of the changes in value Dave ... should not cut be looked at as critically?

Peace,

 

[Rhino]

Date: 9/17/2005 7:45:25 AM
Author: beryl
. Amen, Mr. Atlas. Every stone should be unique, just as people are. Vive la difference.
. This type of ''techie'' talk is not for the consumer. Most of my discussions are off-line with cutters or graders but in this case I jumped-in to help Rhino understand what Brian and John were trying to say. Leonid could make another section of PriceScope for this stuff, but there wouldn''t be enough interest - as happened when DiamondTalk created ''Lapidary'' section for my stuff in late 2002.

PS: I had no knowledge of my illustration being copyrighted; I made it for Brian to help him explain.

Bruce, Brian, John and Paul,

I just wanted to thank you guys for posting what you did and helping me to understand. Without your efforts I would have had no concept of your perspective. One day I''d love to see some of this in action at the wheel over some coffee.

 

[Rhino]

Hey Mike,

I believe, as Bruce does, that any twist, (call it yaw if you must), in the pavilion mains will have uncompensatable consequences in the face-up arrow pattern as well as the face-down hearts pattern.

Couple of questions on the brain as you say this is ...

If we twist a main on a virtual diamond will it *always* result in yaw?

If we twist a main on a real diamond will it always result in yaw?

I''ll do it in diamcalc on the virtual and ask for Johh/Brian/Bruce''s input.