Yaw Angst

[michaelgem]

>I do not mean to intrude in the 'scanner' discussion with these comments so it will be one post and out.
Michael, perhaps if you have comments you will bump either the minor facet thread - or Beryl's azimuth shift/yaw thread? John

The way the forum ages a thread, bumping an old thread does not keep it current very long. These posts seem aged to the back of the bus, so I'll start a new topic. MDC

> here is one set of prior illustrations: minor facet thread page 4 Another set, explaining how his/Paul's observations relate to analysis: minor facet thread page 5. John

I just read these threads and received a very clear and concise, one page, explanation from Bruce at https://www.pricescope.com/community/threads/azimuth-shift-yaw.33257/ .


I now understand the facet twist that is referred to as yaw. As I understand it, what Brian and John call yaw is basically an index 'cheat' or azimuth shift followed by a compensating slope change, so that the facet 'meet points' are maintained. Very clever move, and hard for a scanner or optical comparator to detect, except by girdle measurements. I presume it is done to dig a facet to remove some imperfection or to get a stubborn facet to polish on a 2 or 3-point diamond.


Do Helium’s, Sarin’s or OGI’s scanner software use girdle measurements along with slope measurements to accurately determine the correct slope and azimuth of twisted facets such as these?

Does everyone have the same opinion concerning the impact on diamond beauty or light performance caused by such a twist? It would seem that unless compensating twists were made in opposing facets, the arrow pattern would be disturbed.


Do optically symmetric H&A diamonds have twists that are compensated for and thus not noticed? If the light performance is not affected, does it matter, and what amount of twist would be apparent or materially impact light performance?

What say everyone?
Michael Cowing

 

[michaelgem]

Any change in the facet plane from standard slopes and indexes during gemstone cutting can be uniquely described as a combination of a slope and or azimuth change. These angle changes correspond to the two angle settings on a facetting machine.

Here are definitions of movements of an object such as a plane or rocket: Pitch is up and down like a box lid. Yaw is left and right like a door on hinges, and roll is rotation.

So Pitch = slope. Azimuth or rotation angle = roll.

On a facetting machine the 'cheater' is a screw adjustment allowing deviations from standard indexes. Unlike a pitch or slope change, yaw, defined above as left and right movement, would appear, in relation to a faceting machine, to not change the facet plane at all.

As I understand it, what Brian and John call yaw is basically an index 'cheat' or azimuth shift followed by a compensating slope change, so that the facet 'meet points' are maintained.

If we are compelled to use 'rocket speak' it would appear that the facet twist called yaw is better described to be roll with a compensating change in pitch rather than yaw.

Why not substitute a simple generic term like twist instead of the rocket speak?

Michael Cowing

 

[Rhino]

Michael,

In answer to your first post, I have been collecting graphics, photographs and data to present as a conclusion to all these threads. Brian and I got into a heated discussion on the topic to the point where he exclaimed it is *impossible* for me to do and used some very colorful words.

Hehe... I got so frustrated. I about have all the data collected and I had already began a private letter which I was going to send to you, Garry, Sergey, AGS laboratories and certain research gemologists at GIA whom I know concerning discoveries we are making here with some of the devices you''ve mentioned for a peer review. Because I''m either off my rocker (as Brian suggested in that minor facets thread

) or I am onto something.

If I am too busy tomorrow I''ll have to post it Sunday as or if I can break away from family time as I''ll have my work laptop at home with me. I was going to post it under the thread "what a scanner sees" since I am approaching all of this from a very different angle than what has been introduced by Bruce, Brian and others.

I understand 100% what Brian and John were teaching from the minor facets thread now. Bruce & Paul introduced other elements that kinda threw me off a bit regarding the change in slope, doubling of a facet etc. (which even you admitted ... confusing stuff).

My collegues have been taking the "geometric approach" plus Brian''s optical exam through an H&A viewer on the pavilion. BTW Brian''s discovery takes the science of an H&A viewer to a whole new level when you think about it as this analysis directly shows the optical results of the geometric details Bruce & Paul were pointing out in their illustrations. LOL... I GET IT.

Now I would like to introduce my angle/perspective on all of this but not in the manner that Brian, John, Paul & Ringo ... woops... Bruce did.

My approach is through the crown. Mike ... direct assessment but on a more critical level.

Tools: Helium, DiamCalc, LightScope. 2 technologies developed by Sergey & the MSU staff. Anyone can tell you I had absolutely no involvement in the development of those technologies (except perhaps the now default graphic for IS/FS views in DC which is most similar to our photography than anything else on the planet). LightScope, developed by myself. (I may soon change the name to DiamXray and introduce a different color that may make it easier to point out the features I am examining and patent it). These 3 technologies developed on opposite sides of the planet all correllate. This is the fascinating thing TO ME about the research I am conducting in our lab.

Lord willing I''ll have the time tomorrow. belle... if you are reading this, this is the topic I am talking about. What thread do you think would be most appropriate to post the material? I thought the scanner sees thread because if a person is only focusing on the numbers a scanner produces they would be missing the point and actually introduces "another perspective" the scanner sees than what is being discussed. I want to take this deeper.

What I find a little ironic in all of this ... and you may laugh (I know I did) ... the past 2 weeks ... I swear to you and forum members have seen me go through it ...

I have been forced, in my personal life to consider the perspectives of people whom I was not sensitive to and *see* where they were coming from. Have any of you guys seen the movie with Mel Gibson ... What a Women Wants? Well... I''m not going to say I can read people''s minds but DAM ... DO I FEEL LIKE MEL GIBSON DID IN THAT MOVIE!!! Hehe. A life lesson for me.

On a more geeky level ... we''re now going to consider another *perspective* the scanner sees that many have not (me thinks) been considered. It is really fascinating stuff and I am excited to share.

I''ll look out for a response here tomorrow and post as time allows.

Peace,

 

[Rhino]

On your 2nd post ...

Mike ... it is scary how much we think alike . Did you read my analogy towards the end of the minor facets thread?

I am following you here.

One question I would like to pose to Brian, Bruce and Paul is this.

In the graphic illustrated by Bruce & Brian which in my mind shows this concept really clear, I can understand why Brian would use the term yaw because of the east/west shift of the main. Especially when we relate the terms to "pitch, roll & yaw". If you think about it roll is not yaw, although in "Brian's Yaw" roll is certainly involved. Exactly to what extent it is not clear yet.

The graphic illustrates azimuth shift on all the facets involved. The main that was yawed, plus the two adjoining lower halves.

The main shows a shift @+4.82 degrees azimuth deviation from ideal. The lower half to the left of it (in the face down view) shows an azimuth shift @+4.69 degrees and the one to the right of the main shows a shift @-5.06 degrees.

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?

The reason I ask this question is because it helps answer this one ... *If azimuth deviation from ideal can be identified through the crown, in lower half facets and positive identication can be made *at which orientation they are rotated* ... wouldn't it follow that yaw can be identified through the crown?

I readily admit I am very young in my research on this but this is where I am headed. Illustrations to follow as time allows. BTW here's the graphic for easy reference in this thread.

 

[Rhino]

Thinking deeper on the subject, this is a perfect example of how a diamond could get triple ideal rating PERHAPS EVEN INCLUDING LIGHT PERFORMANCE yet be all screwed up when it comes to optical symmetry.

A subject certain purists like Brian, myself and many others are very fond of.

 

[beryl]

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?"
-----------------------------------------
. Below is blowup of Fig.7 on page 1 of the 'Azimuth & Yaw' thread, and here is partial quote:

. "This drops its interception of the girdle circle 0.0031 = 0.31% at the same point of the circle (an even bigger blowup will show this alignment).
Halves 'A' and 'B' are then twisted and tilted to form a 3-facet meet at this point, and halves 'B' and 'C' are adjusted to bring their meet at the other end to the 80% point ('upper' end in this pic). There are infinite fixes for this twisted and tilted main; I chose this one which most resembles an ideally-cut stone.
Sorry for all this complexity in description (I have to anticipate the 'snipers' out there who will jump on any inaccuracy or ambiguity). It's so much easier to do it - a flick of the wrist and a blink of an eye."

. 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).

 

[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.

 

[beryl]

. Here is Fig.3 referred to above.
. 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.
. Yet one more facet 'C' (Fig.7 in 'Azimuth Twist & Yaw') must be modified to bring the tip of half 'B' back to the same depth as the others. You can see this in the 'copyright' picture of Jan 22, copied above by Rhino.

 

[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.

 

[strmrdr]

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.

Hold.
It has not been proven one way or the other if this is a make or performance issue.
Thats what everyone should be working on in my opinion once everyone can get on the same page as to what it is.

As we have discussed many times there are vast differences in personality in even the best super-ideal cut diamonds that we should be taking into consideration far more than we do.
There is considerable resistance even amounst the vendors here to moving in that direction.
There are some trade offs that are unavoidable and when it comes up they act like one is attacking their products for pointing it out.

 

[Garry H (Cut Nut)]

Yaw seems to have developed into a marketing competiton.

Clearly any diamond facet that is flat can be defined, as Michael says, by slope, azimuth and a point on the facet.

We seem to have established that scanners that do not have algoritms designed to make diamonds appear more symmetrical, can ''see'' the slope and azimuth of twisted facets.*

Meanwhile, we have 2 new grading systems developed by 2 respected organizations, that give a number of stone propotions vastly different cut grades. The better minds at Pricescope seem to be focused on a diversion, that seems to be, well, a diversion.

The biggest change in the industry is happening now, as manufacturers decide what they are going to do. Will they cut more rounds, or less? Will rounds be further commoditized by GIA''s grading, or more differentiated? What will the likely price differences be? Will rapaport add a 4th C to his pricing grids? etc etc


*AGS do not use the facet data from Sarin and Ogi, they have somehow, according to Jim Caudill, been able to take the raw data - not the tinkered with data - for light performance calculations from Sarin and Ogi scans.

 

[beryl]

Quoting Michael Cowing:
. "Does everyone have the same opinion concerning the impact on diamond beauty or light performance caused by such a twist? It would seem that unless compensating twists were made in opposing facets, the arrow pattern would be disturbed."
----------------------------------------------------------------
. Yes and no.
. Twisting a main definitely upsets the arrow pattern.
. Compensating twists on the other side of the stone will not restore it.
. I have illustrated formation of the arrow long ago and will not repeat it here, in deference to Mr. Atlas' comment, unless it seems important to do so. For those who care, see 'DiamondTalk' posts #243027,33 02-02-03. The tip and shaft of the arrow are defined by combined outlines of the near-side main and the far-side main.
. You make a good point, Michael, which will be music to Rhino's ears with his focus on inspection through the crown; such twisting will appear in the arrows - if it is significant; perhaps it will affect the hearts even more - I don't know.

 

[beryl]

Quoting Rhino above:
. "Bruce & Paul introduced other elements that kinda threw me off a bit regarding the change in slope, doubling of a facet etc. (which even you admitted ... confusing stuff)."
-------------------------------------
. Apparently you did not read the following replies I gave in "What a Scanner Sees", Sep 14.

. "The previous thread 'Azimuth Shift & Yaw' was written because Rhino was in doubt about the difference, in another thread. Summary: 'azimuth shift' is just rotation (see Fig.2, which was illustrative only - nobody does this because it creates a double facet); 'yaw' is a combination of azimuth shift and slope increase so that there is only one facet but in the wrong place (Fig.3)." BLH
. I created Fig.2 only to make it easy for you to see that 'yaw' is not just azimuth shift but that plus.
. I did not create the term 'yaw' for cutting (I know what it means in flying); I challenged Brian about it 'back then'. Nevertheless a term for combined azimuth shift and slope change is handy because it is common with all good cutters; if 'yaw' is not suitable, how about 'twist' (but to me that is a curved thing, like a helix). If a word is to be chosen, I'll go along with anything communicative. I had nothing to do with the 'copyright'.

. "Now Paul asks about reflection from a single facet, which has nothing to do with slope - reflection is an optical thing, slope is a geometric thing, as Paul suggested. I will discuss that here or in a separate thread." BLH
. I lied. Instead I made an illustration and text and sent it to Paul privately since it did not belong in this discussion and would have opened another 'bag of snakes' here.

 

[michaelgem]

There are so many good ideas and responses here that I regret not having time right now to respond to them all, but I will as my schedule allows.

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.

IMO a great enough twist will have negative effects on light performance (diamond beauty). Correct me if you think otherwise. I do not believe that either GIA''s or AGS''s measures of light performance currently ''see'' or measure these effects unless they are extreme enough to affect their symmetry grade.

Systematic twists of the halves in the crown and less often in the pavilion, described by cutters and now everyone as painting and digging the halves are another example of purposfull azimuth shifts with compensating slope adjustment to maintain the facet meetpoints. These twists, like twists to the mains, have observable and in some cases intended effects on a diamond cut''s optical performance and beauty. These effects, while leaving the arrow and heart patterns undisturbed do influence light performance positively or negatively depending on your viewpoint. But currently they are not considered in determining the GIA''s or AGS''s cut grade.

Whether you call these slope and azimuth variations, which maintain meetpoints, twist or yaw, if they are of sufficient degree they will affect light performance and diamond beauty. Perhaps most of the discussion may boil down to deciding at what point we should care about these variations, especially if they do not make a perceivable negative impact on light performance or diamond beauty.

Michael Cowing

 

[beryl]

. Yes, Michael. If these minor details attain too much significance, we will never get a universal set of grading standards 'off the ground' - which was my objective at IDCC.
. I believe in 'KISS' (= 'Keep It Simple, Stupid' for the sake of our foreign readers).

 

[michaelgem]

These discussions remind me why I said the following in my recent "Journal of Gemmology" article: Describing diamond beauty - assessing the optical performance of a diamond:

"There are several elements to the quality of a diamond's cut.
Judgments of the elements of cut fall in two distinct categories.

The first category is craftsmanship. Examples of measures of craftsmanship are perfection of polish, facet meet points, facet alignment, symmetry, facet angles and proportions. Most grading of diamond cut being done today makes judgments that fall within this category.

The second category is an assessment of the extent to which all the various factors of craftsmanship have or have not actually resulted in a beautiful diamond. This category is 'direct assessment' of aspects of diamond beauty, as opposed to the indirect assessments of beauty in the first category. Two important examples that fall in this second category are measures of brilliance and fire." Michael Cowing

Azimuth shifts of mains or halves with compensating slope adjustment to maintain standard facet meetpoints (the standard wire frame) are great examples of cutting variations that can attain the highest score in craftsmanship based cut grading systems, such as the BrayScore by well known and highly respected diamondtaire, Bill Bray.

But at the same time these variations can have a positive or negative affect upon aspects of diamond beauty such as brilliance and fire.

Unless some form of 'direct assessment' of light performance is done, a diamond cut may achieve the highest rating in a cut grading system based upon craftsmanship, while an evaluation of its light performance and perceived beauty would judge it less positively.

Michael Cowing

 

[Garry H (Cut Nut)]

Date: 9/17/2005 11:34:10 AM
Author: michaelgem
IMO a great enough twist will have negative effects on light performance (diamond beauty). Correct me if you think otherwise. I do not believe that either GIA''s or AGS''s measures of light performance currently ''see'' or measure these effects unless they are extreme enough to affect their symmetry grade.
Michael Cowing

GIA do not "measure" light performance. Their system is parametric (based on proportions - like HCA, but with a small impact from 5% rounded upper and lower girdle facet length). But they have stated that they are on the lookout for indexed upper and lower girdle faceting.

AGS do measure light performance by using 3D scanned models with ray tracing software. So they will capture some type of actual results that result from twisted or asymmetric facets.

Both AGS and GIA have published and presented information on idexing / digging / gouging / painting etc

(BTW gentlemen, to use the Quote function, simply reply to the post that you wish to quote. Then when the dialogue box opens, hit the Quote button that is in the upper left just below "attach File".

If there is stuff you want to remove, you can use a complex double click etc and cut and remove stuff.
For instance here is the entire post below, that I edited down for easy reading.

Date: 9/17/2005 11:34:10 AM
Author: michaelgem
There are so many good ideas and responses here that I regret not having time right now to respond to them all, but I will as my schedule allows.

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.

IMO a great enough twist will have negative effects on light performance (diamond beauty). Correct me if you think otherwise. I do not believe that either GIA''s or AGS''s measures of light performance currently ''see'' or measure these effects unless they are extreme enough to affect their symmetry grade.

Systematic twists of the halves in the crown and less often in the pavilion, described by cutters and now everyone as painting and digging the halves are another example of purposfull azimuth shifts with compensating slope adjustment to maintain the facet meetpoints. These twists, like twists to the mains, have observable and in some cases intended effects on a diamond cut''s optical performance and beauty. These effects, while leaving the arrow and heart patterns undisturbed do influence light performance positively or negatively depending on your viewpoint. But currently they are not considered in determining the GIA''s or AGS''s cut grade.

Whether you call these slope and azimuth variations, which maintain meetpoints, twist or yaw, if they are of sufficient degree they will affect light performance and diamond beauty. Perhaps most of the discussion may boil down to deciding at what point we should care about these variations, especially if they do not make a perceivable negative impact on light performance or diamond beauty.

Michael Cowing

 

[JohnQuixote]

Date: 9/16/2005 7:14:27 PM
Author:michaelgem
I now understand the facet twist that is referred to as yaw. As I understand it, what Brian and John call yaw is basically an index 'cheat' or azimuth shift followed by a compensating slope change, so that the facet 'meet points' are maintained. Very clever move, and hard for a scanner or optical comparator to detect, except by girdle measurements. I presume it is done to dig a facet to remove some imperfection or to get a stubborn facet to polish on a 2 or 3-point diamond.

Michael, yaw has been identified as the resultant effect of azimuth shift, when the facet has been polished in an East to West or West to East direction. Your description above may serve as a good elaboration - one of the primary causes is when the cutter can't get the facet to run and uses that cheater as you describe when polishing.

Date: 9/16/2005 7:14:27 PM
Author:michaelgem
Do Helium’s, Sarin’s or OGI’s scanner software use girdle measurements along with slope measurements to accurately determine the correct slope and azimuth of twisted facets such as these?

This is the question. Serg has been active in these threads - I hope he'll address the helium portion directly with Brian, perhaps privately.

Date: 9/16/2005 7:14:27 PM
Author:michaelgem
Does everyone have the same opinion concerning the impact on diamond beauty or light performance caused by such a twist? It would seem that unless compensating twists were made in opposing facets, the arrow pattern would be disturbed.

To a degree Michael, but a problem with attempted crown analysis is that any effects yaw/twist have on optical performance is hindered due to obscuration. Check these several posts with illustrations and see what you think.

Date: 9/16/2005 7:14:27 PM
Author:michaelgem

Do optically symmetric H&A diamonds have twists that are compensated for and thus not noticed? If the light performance is not affected, does it matter, and what amount of twist would be apparent or materially impact light performance?

What say everyone?

Jump on down and see the type in GREEN, in my next post.

Date: 9/16/2005 7:46:35 PM
Author: michaelgem

As I understand it, what Brian and John call yaw is basically an index 'cheat' or azimuth shift followed by a compensating slope change, so that the facet 'meet points' are maintained.
If we are compelled to use 'rocket speak' it would appear that the facet twist called yaw is better described to be roll with a compensating change in pitch rather than yaw.

Why not substitute a simple generic term like twist instead of the rocket speak?

Michael Cowing

I thought Rhino's explanation was good.

Date: 9/17/2005 11:34:10 AM
Author: michaelgem

...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.

IMO a great enough twist will have negative effects on light performance (diamond beauty). Correct me if you think otherwise. I do not believe that either GIA's or AGS's measures of light performance currently 'see' or measure these effects unless they are extreme enough to affect their symmetry grade.

Systematic twists of the halves in the crown and less often in the pavilion, described by cutters and now everyone as painting and digging the halves are another example of purposfull azimuth shifts with compensating slope adjustment to maintain the facet meetpoints. These twists, like twists to the mains, have observable and in some cases intended effects on a diamond cut's optical performance and beauty. These effects, while leaving the arrow and heart patterns undisturbed do influence light performance positively or negatively depending on your viewpoint. But currently they are not considered in determining the GIA's or AGS's cut grade.

Whether you call these slope and azimuth variations, which maintain meetpoints, twist or yaw, if they are of sufficient degree they will affect light performance and diamond beauty. Perhaps most of the discussion may boil down to deciding at what point we should care about these variations, especially if they do not make a perceivable negative impact on light performance or diamond beauty.

Michael Cowing

We think some will be negative, but some are potentially positive. Yes, 'deciding at what point we should care' is key. I really do think this is totally unecessary for most consumers - present company obviously excepted. Sans a cut-tech forum, here we be and here we stay. Less personal preferences in posts (from some, not you), keeping background noise to a minimum, not running off on tangents and not frightening the masses - who really don't give a didgeridoo about all this - is all key to successful discussion.

Date: 9/17/2005 12:22:20 AM
Author: Rhino
My collegues have been taking the 'geometric approach' plus Brian's optical exam through an H&A viewer on the pavilion. BTW Brian's discovery takes the science of an H&A viewer to a whole new level when you think about it as this analysis directly shows the optical results of the geometric details Bruce & Paul were pointing out in their illustrations. LOL... I GET IT.

LOL myself. Thanks, and thanks also for your contact the other day to that effect. I can't wait for your banner ad... "It's All In The Hearts."

(ducking)

Date: 9/17/2005 12:22:20 AM
Author: Rhino
What I find a little ironic in all of this ... and you may laugh (I know I did) ... the past 2 weeks ... I swear to you and forum members have seen me go through it ...

I have been forced, in my personal life to consider the perspectives of people whom I was not sensitive to and *see* where they were coming from.

Again, thanks for the considerate contacts and the phone convo the other day. Your input, specifically your hours invested in infinitesimal analysis, is valuable as has been said many times. No sweat - all of us sometimes need a reminder to keep it 'real.'

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.

Dave, it is not the roar of the ocean you are hearing - it is the deafening applause.

Yes, from Brian this was all observations on - and information for - cut development first, optics second. Brian has already provided much guidance to cutters to reduce this phenomenon in initial blocking. Like many here his goal is improvement of worldwide cut. As for diamond grading and what is practical - you're right. There are no plans for major labs to begin grading optical symmetry (the only domain where this would be assessed). This discussion, and Brian's grading system for optical symmetry, serve a niche market of consumers and enthusiasts at best, but the discussion serves ALL craftsmen and cutters wanting to further understand their profession. As for practicality, we must keep it real.

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, I was the one who placed the copyright on that page, intending only to protect your work. It was a precaution only. If you prefer the copyright be removed I will do so with pleasure.

Date: 9/17/2005 7:45:26 AM
Author: strmrdr
Hold.
It has not been proven one way or the other if this is a make or performance issue.
Thats what everyone should be working on in my opinion once everyone can get on the same page as to what it is.

As we have discussed many times there are vast differences in personality in even the best super-ideal cut diamonds that we should be taking into consideration far more than we do.
There is considerable resistance even amounst the vendors here to moving in that direction.
There are some trade offs that are unavoidable and when it comes up they act like one is attacking their products for pointing it out.

I wonder about use of the word 'vast.'

Date: 9/17/2005 8:02:49 AM
Author: Garry H (Cut Nut)

Yaw seems to have developed into a marketing competiton.

Yep Garry, there are hints of marketing on several fronts and they are not limited to diamonds. This doesn't mean anyone's input is invalid, but I agree it can cause interference. Those who do not have ties to specific diamonds/devices or philosophies are giving generously, and I hope the usual suspects can work through our collective ties - and find unified definitions and answers as we have in the past.

 

[JohnQuixote]

Look at the limos. It is great to see the VIPs coming out to the yaw party! Grab a flute of bubbly and you MUST try the crab cakes. We'll be having a dance contest later... Doing 'The Twist' of course.

By the way Michael - the thread's title is perfect.

Brian withdrew from these threads some time ago, when the focus was split into speculation of crown assessment over pavilion - we were nowhere near ready to try and identify performance issues, since we had not arrived at consensus on a definition or what machines can 'see' what we have not yet defined. There are several discussions that have started in these threads. Maybe we can sort them into less of a jambalaya.

Brian first presented this information to bring forward these questions:

(1) Can we have a discourse of fine make cut/craftsmanship and arrive at a definition of what is observed as yaw?
(2) Can we agree that the simplest way to observe pavilion facet construction details (NOT performance) is with a H&A viewer?
(3) Knowing we can see it through a H&A viewer - Which of the scanning machines, if any, pick it up?
(4) FINALLY (save it for last) - What potential does yaw have to influence light performance?

So, where are we on these? As I see it...

(1) The discourse is occuring. Great. Let's please continue. Between Brian, Paul, Bruce, Serg, Garry & Michael we have the world's top cutters and scientists in one place... Bartender!

(2) Clear H&A viewer pavilion assessment is known fact. Though lightscope/DiamXray may prove intriguing later, promoting observation through the crown is putting the cart before the horse right now. The crown arguments should be saved for question 4 when we talk about possible performance impact. We're not to that question yet since questions 1 and 3 need to be answered. We know we can see these things clearly in the pavilion view of the H&A viewer. Perhaps we should stick to that?

(3) The discourse is occuring to some degree, but I suggest Serg and Brian should have it unimpeded.

(4) Maybe we can refrain from trying to answer this until we agree on (1) (2) and (3). I know that to many this is the key question but I suggest we talk craftsmanship/cut in order to come to a unified understanding. Trying to do assessment without everyone on the same page seems futile.

We are NOT YET at question 4, but many have voiced that, in the absence of such a question, we needn't bother. Dave soundly offers that these may be things normal consumers don't even need to bother with - and could cause worry that is totally unecessary. I agree completely. But there are purists and enthusiasts who enjoy making the slightest distinctions and that makes the topic worthy of discussion - BUT NOT HYPE. Let's keep it 'real.' Yaw deviations may be only as influential as slight polish or meet point deviations... Or perhaps have more influence?

For Dave and others who have asked about the implications. When we DO discuss performance aspects here are three 'angles' (haha) to consider:

(a) Marty Haske is doing studies on the nature of dispersion with supersymmetry. In such diamonds it is possible that the spectral colors you see will be more pure and robust - less pastels and earth tones - due to precise alignment. His research and the dynamics of yaw will no doubt handshake.

(b) One thing we've noticed is that a moderate level of pavilion angle variance is no problem as long as the diamond has minimal yaw to the factes and the opposites average. There is no adverse visible effect - as a matter of fact the quality of scintillation may benefit from some variance as long as it is north-south. In such a well cut diamond the averaging of opposite facets is the important thing, so more variance is acceptable (and desirable) for cut purists in a diamond with no/minimal yaw.

(c) For those who are not fond of supersymmetry, the presence of yaw in a pattern may be of benefit, as if could enhance the chaotic nature of the performance - so long as yaw is not so severe that light returns at undesirable low angles.

I hope Brian will put down his loupe, turn his computer back on and make comment, as this 'Angst' thread could be a place to refocus. For other esteemed experts participating - I'd appreciate input on the q's outlined above.

 

[michaelgem]

"GIA do not "measure" light performance. Their system is parametric (based on proportions - like HCA, ..................
AGS do measure light performance by using 3D scanned models with ray tracing software. " Garry Holloway

As I and others such as David Atlas have pointed out, neither the AGS nor the GIA system is making a 'direct assesment' of light performance from images of the actual diamond.

They both make predictions of light performance from parametric computer models using data from Sarin machines. They both purport to apply light performance metrics to these parametric models using 'ray tracing' to help arrive at a cut grade.

AGS may use the full raw data, while GIA averages the data and applies its metrics to an idealized model using average angles and percentages.

Neither is doing direct assessment. Both believe their systems sufficiently accurately predict the diamond's cut quality and resulting performance and beauty in accordance with human judgment.


Michael Cowing

 

[michaelgem]

I do not believe that currently available software, that predicts light performance from the output data of Sarin and OGI, whether complete or averaged, is sufficiently predictive of a diamond’s actual light performance.

I am hopefull that improvements to the technology, such as the promise of the Helium machine and its processing software, will enable sufficiently accurate predictions of actual diamond light performance.

In the mean time, I continue to believe that direct assessment of light performance from images of the diamond , face-up and tilted, taken in a representation of typical lighting and viewing circumstances is best.

Even if technology improvements allow computer models to enable light performance assessement comparable to assessment from actual images of the diamond, will the lab's metrics continue to miss aspects of light performance that many feel differentiate their diamond cut as superior? Or will these aspects remain a matter of taste in the eyes and opinions of the labs?

These are big picture questions. Any opinions as to answers? Perhaps how it all shakes out will be influenced in large part by how all this is marketed by the diamond cutting houses, the labs, the Internet and jewelers.

Michael Cowing

 

[strmrdr]

From what Iv heard:
AGS is using helium scanners to generate the data for the diamonds it applies the new cut grade too on its grading reports.

 

[JohnQuixote]

Actual ASET reflector analysis figured prominently into the development of the new AGS light performance grade. AGS is using software combining their optical ray tracer with custom algorithms and logic, but they are also using live ASET imagery as quantification for the software and vice versa.

 

[michaelgem]

Date: 9/17/2005 9:23:15 PM
Author: JohnQuixote

Actual ASET reflector analysis figured prominently into the development of the new AGS light performance grade. AGS is using software combining their optical ray tracer with custom algorithms and logic, but they are also using live ASET imagery as quantification for the software and vice versa.

Both GIA and AGS have performed extensive testing and both believe they have verified that their software modeling of their metrics, illumination and the diamond adequately accord with analysis of ''live imagery''.

Michael Cowing

 

[Rhino]

ugh... just typed out long response.... timed out ...

I'll come on tomorrow as time allows. Lots to write but sleepy now.

John... the answer to question 4 answers 3 also but I will not jump ahead.

more tomorrow...

 

[JohnQuixote]

Date: 9/18/2005 1:33:07 AM
Author: Rhino
ugh... just typed out long response.... timed out ...

I'll come on tomorrow as time allows. Lots to write but sleepy now.

John... the answer to question 4 answers 3 also but I will not jump ahead.

more tomorrow...

HATE it when that happens! When I know it might be wordy I've moved to doing the reply in a word processor b/c of that very thing.

I see where 4 & 3 may overlap... Appreciate the no-jump just yet

We still need to come to consensus on #1 from the current cut cadre. Those who've weighed in are seeing eye to eye on #2 - for observation of live construction particulars - not performance.

Any dissenters? Or do we have an aye for an aye?

 

[Garry H (Cut Nut)]

Date: 9/17/2005 8:44:08 PM
Author: michaelgem

''GIA do not ''measure'' light performance. Their system is parametric (based on proportions - like HCA, ..................
AGS do measure light performance by using 3D scanned models with ray tracing software. '' Garry Holloway

As I and others such as David Atlas have pointed out, neither the AGS nor the GIA system is making a ''direct assesment'' of light performance from images of the actual diamond.

They both make predictions of light performance from parametric computer models using data from Sarin machines. They both purport to apply light performance metrics to these parametric models using ''ray tracing'' to help arrive at a cut grade.

AGS may use the full raw data, while GIA averages the data and applies its metrics to an idealized model using average angles and percentages.

Neither is doing direct assessment. Both believe their systems sufficiently accurately predict the diamond''s cut quality and resulting performance and beauty in accordance with human judgment.


Michael Cowing

Michael do you really believe GIA are using any form of ray tracing or computer analysis in their new grading system?

I have noticed that some diamonds that rate Excellent in their new proportion grade Facetware software fare very poorly on both WLR and DCLR.

GIA were originally intending to study scintillation with their software. Since they never publishhed anything (AGS also have not yet cracked the scintillation code), it seems unlikely that GIA is using any part of its expensive computer based studies.

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. The simple fact that none have been prepared to release for peer review any truly objective data, seems to indicate that little or no such studies have been done, or the results were "inconclusive".

 

[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. The simple fact that none have been prepared to release for peer review any truly objective data, seems to indicate that little or no such studies have been done, or the results were ''inconclusive''.

Garry:
. The above is well-written; please tell me what ETAS means.
. Thanks for telling us how to remove parts of quotes.

 

[beryl]

Date: 9/17/2005 6:57:32 PM
Author: JohnQuixote

Bruce, I was the one who placed the copyright on that page, intending only to protect your work. It was a precaution only. If you prefer the copyright be removed I will do so with pleasure.

John:
. I just wanted the folks to know that I am not ''in bed'' with anyone. I am a free-agent interested in helping all.
. I have been ''suspected'' by appearing to be affiliated with certain parties, for defending them, or for getting credit which was not mine; this has impaired my communication with other parties.

 

[beryl]

. I read above - but can''t find it to quote - that the study of arrows was impaired by obscuration. The arrow IS CAUSED by obscuration - without it there is no arrow.