Optical Symmetry Sweetspot...Which AGS000?

[delonn]

Although my heart was pushing for the ASET, the arrows sent me to the IS. Hopefully, I''ll get it soon...


John,

I have no qualms w/ being transferred to another DC or DCs paid on commission. What I do have an issue w/ is not answering questions directly (e.g., Can you qualitatvely describe the inclusion, why it costs $90 to ship a dimaond that is in stock?, etc.). Each time a question was skirted, it led me to want to get further detail. While Katie''s inadvertent e-mail was certainly not offensive, I think most would consider it unprofessional to a client that was willing to spend $20k. No harm, no foul...

 

[diamondseeker2006]

delonn,

This is sort of interesting because I am looking at some similar stones. Did you by any chance see the 1.63 H VS1 that Good Old Gold had a couple of weeks ago? It happens to be on hold for me. I am having it shipped along with another stone this week to look at. I know there was someone else interested in it and I wonder if it was you. It would be an excellent choice for someone if I don''t keep it. It is perfect...but I may not keep it if I think it is too big. The other stone is a little smaller.

 

[delonn]

When I went to purchase that stone, someone snatched it...just kidding.

Actually, I did review that stone and the only thing that I wasn''t really excited about was the size at 1.63. It has perfect H&A, the exclusion is on the table but not noticeable, and meets the <2 criteria. Can you remind me what the price point was? I cannot remember why I didn''t pursue it but I''m pretty sure that it was solely becuase it was smaller than what I am considering. It''s looks like a great stone and it''s from GOG so I''m sure you''ll be happy. Let us know what you decide to do...

 

[diamondseeker2006]

Date: 7/10/2006 11:35:44 PM
Author: delonn
When I went to purchase that stone, someone snatched it...just kidding.

Actually, I did review that stone and the only thing that I wasn't really excited about was the size at 1.63. It has perfect H&A, the exclusion is on the table but not noticeable, and meets the <2 criteria. Can you remind me what the price point was? I cannot remember why I didn't pursue it but I'm pretty sure that it was solely becuase it was smaller than what I am considering. It's looks like a great stone and it's from GOG so I'm sure you'll be happy. Let us know what you decide to do...

Lol! Even though it is 1.63, it is 7.6mm, so it is very close in size to the others you were looking at, that's sort of why I mentioned it! It was around $14,000. I live in an area with pretty small diamonds, so I am not sure I'll be comfortable jumping from a 1.0 to 1.6. I hope I can talk myself into it, though! It scored high H to G on the color meter and the inclusion is minute. I just wanted you to know that I'd be deciding one way or another very soon (I am hoping to post pictures when the stones come). But I'm sure you can find a 1.7-1.8 stone of similar quality. Jonathan is good at searching for them!

 

[delonn]

Yes, I did notice that this stone has a great spread as well. One thing thing that I considered was the setting that I was planning to use. Since I am planning to mount the diamond up high, a concern was that the girdle might be too thin and chip. I think AGS Ideal range is from 2.2-4.99% and the 1.65 is probably ~1.5%. Not a deal breaker but a consideration for me. Btw, where did you see the G-H color rating on it?

Out of curiousity, what is the other stone that you are considering?

On another note, you''ve been registered w/ PS for 6 months; have you been searching for the right stone all this time...case of DOCD?

 

[diamondseeker2006]

delonn, no, this stone has ideal proportions. The girdle is thin to medium, faceted. It has a desirable girdle. It is only very thin that you want to avoid in regard to chipping. Look here under class 1A American Ideal Cut.

http://diamonds.pricescope.com/round.asp

Thin to medium is 1.0-3.0 and med. to sl. thick is 1.7-4.5. Those are the most desirable ranges. The more thickness in the girdle, the more weight is there, which reduces the diameter. Jonathan has a machine called a colorimeter, and it registered above H and into the G range for this stone. The other stone measured a solid H, which I am not sure how I feel about until I see it. It is a 1.37 cts. stone and is closer to the size I was originally looking for. Our anniversary isn't until December, so I haven't had any time pressure. I really wanted a stone just under 1.5, but they are hard to some by! I had seen the 1.63 and thought it was almost perfect for me, except that it is a little larger than I wanted. But we decided to consider it, because it is so great otherwise. So one stone is about 7.2mm and the other is 7.6mm, two different sizes altogether.

ETA: Yes, I do have DOCD for sure.

 

[Rhino]

Hi delonn,

Just returned from our weekend and caught this thread. It happens to be a subject I am very fond of and would like to address your questions though I see some were answered in part.

Date: 7/9/2006 4:48:39 AM
Author:delonn
Last week, I purchased an AGS000 and while the HCA came in at 1.9 (Ex, VG, VG, VG) I wasn't entirely happy with the cut (thanks to PS, I've become fickle). Specifically the optical symmetry was one of the worst that I've seen among AGS000s. Although I think it is nearly impossible to be assured of H&A from a cert alone, I believe that most H&A (or near H&A) fall in a specific range of values. While we can argue about how broad this range is, it seems from the 'Search by Cut' tool in Pricescope that there is a sweet spot range. For example, Garry mentions that most H&A diamonds fall in the upper TIC range (the range looks to be 1.1-1.7 in HCA) and the vast majority of H&A diamonds listed have pavilian angles of 40.6-40.8 - which may preclude them from the ultra-low .4-.7 range. Similarly, I have yet to see a H&A w/ a 40.4 pav. angle or above a 62.3% depth. Given my anecdotal analysis, I am trying to determine which stone might have the best optical symmetry based on Cert data alone.

My hypothesis is that if a stone is within a strict proportion range (e.g., AGA 1A) and meets proven pav/crown combos (from PS 'Search by Cut'), one can predict with near certainty that a stone will have excellent optical symmetry. This may seem intuitive but I have yet to see a robust tool to predict H&A. In other words, would it be fair to say that a diamond w/ a certain H&A combination of pavilion/crown angles coupled with AGA 1A stats is reasonably likely to exhibit excellent H&A?

Unfortunately no. At least not with the Sarin's being offered today UNLESS it can generate an accurate 3d model which can be further inspected in ray trace software such as DiamCalc (but then you're going beyond the basic sarin numbers).

Quality of optical symmetry (craftsmanship) can be determined by the numbers but an intimate knowledge of which sets of numbers produce the H&A phenomena and also a knowledge of the measurements of every facet must be considered. Both slope and azimuth angles. The only scanner I know of that provides these numerical details is the Helium scanner.

For example, you can have a diamond with cherry angles when considering the averages yet be an optical disaster when considering craftsmanship. This IMO is where both GIA and AGS fall short in their new cut grading. Optical symmetry is a direct reflection on craftsmanship and the factory that takes its time to do the job right, in my professional opinion should be rewarded for that time and effort it takes to produce precise optical symmetry.

Pertaining to the numbers ...

Attached is a stone we've scanned in and if you take a look at both the averages and the min/max deviations it shows to be a pretty tight stone.

Only a .44 degree deviation from min to max on the crown angles (when considering all 8 bezel measurements)
Only a .31 degree deviation from min to max on the pavilion angles (....................... all 8 pavilion main ..........)
Only a .34 % deviation from min to max table measurements.

Argh ... I'm having trouble attaching pix for some reason.

I'll try and do a copy paste of the data here in this post.

*EDITED TO ADD ... GOT THE GRAPHIC POSTED IN NEXT POST*

Parameter Avg Min Max Dev Cut Sym
Diameter mm 7.126 7.112 7.143 0.44 % 0 EX
Crown angle ° 34.31 34.03 34.47 0.44 0 EX
Crown height % 15.03 14.92 15.14 0.22 N/A EX
Crown height mm 1.071 1.064 1.079 0.015 - -
Crown height at girdle minima % 15.82 15.67 15.91 0.24 N/A -
Crown height at girdle minima mm 1.128 1.117 1.134 0.017 - -
Pavilion angle ° 40.95 40.78 41.09 0.31 N/A EX
Pavilion depth % 43.15 43.03 43.24 0.21 0 EX
Pavilion depth mm 3.075 3.067 3.082 0.015 - -
Pavilion depth at girdle minima % 44.05 43.86 44.18 0.31 N/A -
Pavilion depth at girdle minima mm 3.139 3.126 3.148 0.022 - -
Lower girdle facets angle ° 42.11 41.92 42.24 0.32 - EX
Lower girdle facets height % 35.40 35.13 35.63 0.50 - EX
Lower girdle facets height mm 2.523 2.504 2.539 0.035 - -
Depth Girdle Facet % 79.64 79.02 80.18 1.15 N/A -
Length Girdle Facet % 77.93 77.33 78.42 1.09 - -
Upper girdle facets angle ° 40.96 40.51 41.75 1.24 - VG
Upper girdle facets height % 10.46 10.07 10.77 0.70 - -
Upper girdle facets height mm 0.745 0.718 0.768 0.050 - -
Star facets angle ° 22.65 22.19 23.14 0.94 - EX
Star :
Upper ratio % 53.27 :
46.73 51.23 :
48.77 55.05:
44.95 3.82 - FR
Table % 55.89 55.75 56.08 0.34 0 EX
Table mm 3.983 3.973 3.997 0.024 - -

Sorry if this appears crude. I'll try later to post the table in a graphic as it is in the Helium. But you get the gist.

By these measurements the stone shows to be pretty tight.

 

[Rhino]

Yay. I just rebooted and ran Norton ... now I''m able to attach. Disregard that copy/paste this is much easier to read. I highlighted the crown/pavilion/table data noting how tight the variances are in these facet sets.

 

[Rhino]

Ok ... here are how far the azimuth angles deviate from ideal on this particular stone.

(note: slope angles are those angles commonly reported on Sarin/OGI/Helium scans and run in the north/south orientation. Since diamond is a 3 dimensional object, each facet is not only cut to a north/south orientation but also an east/west orientation as well. Azimuth angles are those that run in a east/west orientation._

All of them are also pretty tight on both the crown and pavilion.

However ... note that one of the lower halves deviates from ideal -1.27 degrees and one bezel facet on the crown .95 degrees from ideal (which I''ve highlighted in the graphic below).

 

[Rhino]

Argh ... having trouble with graphics upload again.

I''ll have to try again later to upload.

In any case, that small deviation in azimuth angles prevents this stone from getting our "ideal" optical symmetry grade and is near ideal. That deviation causes one heart that is notably smaller than the others.

So there are a few things that can contribute to screwing up optical symmetry. Those being ...

a. Wild varianes in crown/pavilion angles.
b. Variances in lower girdle facet length (there are 16 of them).
c. Deviation in azimuth angles from ideal.
d. Out of roundness of the diamond in general.

Ie. details on all the facets must be provide.

Optical symmetry on even cherry proportions can range from ideal, to near ideal, to common (chaotic). Physical inspection by a professional of course is always the best with photography to prove it.

Kind regards,

 

[delonn]

VERY insightful Rhino! Hopefully, your data on optical symmetry will become a new metric on the next generation AGS and GIA certs. I''m not sure how feasible this would be but it would make diamond shopping even more transparent.

Diamondseeker- Where else can you get detail like that to satisfy your (our) DOCD? Buy one of those diamonds already...you simply cannot make a bad decision. I''m surprised that the bigger diamond is ~$14000 as I recall it being it would have been higher than I am willing to spend. Either way, let us know what you decide.

As for the size, I was also concerned about getting a stone that was too large for my gf''s size 5 finger. My girlfriend is quite modest and after attending a wedding this past weekend, I realized that a 1.7 might be the biggest diamond she''s seen. The funny thing about this whole process is that she probably will have no idea the lengths that I''ve gone to find her the right stone. At the end the day, no one in their rightful mind would pay that kind of money for a piece of carbon if there wasn''t some emotional or social value. To this end, I don''t think that you can go wrong w/ a larger stone although it may make for some awkward moments. The only the thing that has stopped me from downsizing is that I don''t want to prolong the search any longer than I have to.

Best,

DeLonn

 

[Garry H (Cut Nut)]

Hey Delonn - I am sure she knows you are OCD

And aGS do not believe high level optical symmetry is as important as basic light return.

What Rhino is talking about can be accomplished with Bill Brae''s Brae Score - he posts here - you may have read something he mentioned on this post I think?

 

[Paul-Antwerp]

Date: 7/11/2006 1:44:18 PM
Author: Rhino
Argh ... having trouble with graphics upload again.

I''ll have to try again later to upload.

In any case, that small deviation in azimuth angles prevents this stone from getting our ''ideal'' optical symmetry grade and is near ideal. That deviation causes one heart that is notably smaller than the others.

So there are a few things that can contribute to screwing up optical symmetry. Those being ...

a. Wild varianes in crown/pavilion angles.
b. Variances in lower girdle facet length (there are 16 of them).
c. Deviation in azimuth angles from ideal.
d. Out of roundness of the diamond in general.

Ie. details on all the facets must be provide.

Optical symmetry on even cherry proportions can range from ideal, to near ideal, to common (chaotic). Physical inspection by a professional of course is always the best with photography to prove it.

Kind regards,

I agree, but disagree, Jonathan.

Yes, it is important and useful to get information on all facets. Too many inconsistencies can be hidden in averages, and if you really want to go into the nitty-gritty detail of getting the best of the best, you owe it to yourself to get info on all the facets.

However, I disagree with the stone in your example. I personally do not think that, in the angles, it is a tightly cut stone. To my taste, there is too much variation in the pavilion. Remember that the pavilion is the foundation of light-return, and also, that the cut of the pavilion is much easier to control than the crown. As such, we need and at the same time can expect more tightness in the pavilion than we can expect in the crown-area.

Therefore, your conclusion that some lack of optical symmetry is due to a minute azimuth-shift seems like jumping to the gun. I have the impression that there are various factors at play, and the main culprit is the variation in the pavilion area. At least in this particular stone.

All in all, the subject of optical symmetry is very important, and I cannot stress its importance sufficiently. And while cutting with minimal variations, the result is not only a beautiful H&A-pattern, or another symmetry-pattern in princesses for instance, but also extreme crispness in that pattern, due to minimization of variances.

Therefore, an extremely important topic, and one can only verify it with a full 3D-scan of the stone.

Live long,

 

[strmrdr]

Paul, what pavilion variation do you consider tight?
My personal ocd level is:
.2 and under kicken
.2-.3 exellent
.3-.35 very good.

For the crown I like to see it in the .35 range and under for kicken and up to .5 as exellent.

 

[WinkHPD]

I believe that you will find most of Paul''s stones to have variences of no more than 0.2 for the pavilion and 0.4 for the crown. I will leave the exact answer to him but that is what I have come to expect.

Wink

 

[Paul-Antwerp]

Date: 7/12/2006 6:30:45 AM
Author: strmrdr
Paul, what pavilion variation do you consider tight?
My personal ocd level is:
.2 and under kicken
.2-.3 exellent
.3-.35 very good.

For the crown I like to see it in the .35 range and under for kicken and up to .5 as exellent.

We try to keep it at 0.1 for the pavilion on our factory-measurement, but, on other measurement-devices, this often translates into 0.2° difference. However, we also have stones which give a completely flat measurement.

In the crown, the tools give you less possibility of control, but on the other hand, in light performance, the pavilion is the foundation and the crown is also secondary. However, we aim for a variation of maximum 0.4° in the crown.

Just to give some background-info on the tools: the stone is put in a tang, and basically, the stone is in a circular movement, while it is being cut. This means that the angle of the facet constantly decreases, while it is being cut, and the final angle is only established after the facet is finished. Especially, when cutting the pavilion-side, one can only measure the actual facet-angles after the pavilion is completely cut. One cannot finish one facet, measure it on the machine, re-set the stone in the tang, and continue working on the other facets. One has to finish the whole pavilion, and only then, one can measure the resultant angles of the cutting-process. This shows how critical it is to know your tools, know your diamonds and to control your work while cutting.

A few years ago, in an effort to improve quality-control during cutting, I designed a tang, in which the facet is not cut in a circular movement, but in a completely vertical movement. Thus, the facet-angle does not change while cutting, and the cutter can correctly establish the angle before he starts working. The problem is that the cutters at the wheel cannot adjust their way of working to this new tool. Plus, it also constrained their way of working in such a way, that they could not obtain the very best quality on polish, when working with this new tang-system. So, in the end, my design-efforts were in vain.

Live long,

 

[strmrdr]

Thanks Paul, interesting stuff.
If you dont mind answering which scanner do you use in house?
If you would rather not say thats kewl.

 

[WinkHPD]

Fascinating, I think, that with our modern technology we try to invent better ways to do things than the "ancients" and so often, at least in the world of diamonds, we find that the "ancients" with no computers and with farily primitive technology were incredibly right on with what they did and how they did it.

Some of you may remember the large matrixes that I posted after the AGS class that I took on cut grading showing the "sweet spots" for light return. These charts were the results of ray tracing 62,500 possible crown and pavilion angles for a given table size. Peter Yantzer showed these to me the afternoon before the class and there was a definite note of awe in his voice as he showed them to me. "Isn''t it amazing?" he said, "That without computers the old cutters new exactly where the sweet spot was?"

Paul, you never told me that you had invented a tang like that, and I have to agree with you that it sounds like it should have made it easier to obtain the extremely tight tolerances that you seek. Did you also find it (other than frustrating) amazing that the old way actually worked better, in spite of seemingly being the hard way to get the angle? Still, with pavilion tolerances of 0.2 or lower, I think I should not like to be one of your cutters!

Wink

 

[Garry H (Cut Nut)]

Intersting Paul - I guess grinding of 1mm would be an angle change of about .25 degrees if my lousy trig is about right.
Anyone good at that?
If the tang is about 250mm long from feet to stone.

 

[Paul-Antwerp]

Date: 7/12/2006 7:53:55 AM
Author: Garry H (Cut Nut)
Intersting Paul - I guess grinding of 1mm would be an angle change of about .25 degrees if my lousy trig is about right.
Anyone good at that?
If the tang is about 250mm long from feet to stone.

I am too lazy to do the calculation.

The difficulty is that the support-plate (on which the tang rests), the wheel and the tang itself must be exactly level at the point in time that the facet is finished.

And for each different size of stone, this means adjusting the setting of the tang (also because angle-changes between mains and halves will have different effects).

Many cutters therefore have different tangs for different sizes of stones.

Live long,

 

[Paul-Antwerp]

I have the impression that I am giving away too much info on various technicalities. I will have to refrain myself.

Live long,

 

[diamondseeker2006]

You guys do nothing to help diamond OCD. It was bad enough having to look at crown and pavilion angles. Now you want us to look at the helium scans for crown and pavilion variation. I feel like a master''s in physics is required to pick out a diamond!

Delonn, I''ll have to say that in SC, anything over 1.5 is very large. I got engaged long ago with a 1.0 ct., and it has always been on the higher end of size most places I''d go. I also have small fingers, so these stones look even bigger. Now that you are moving to NY, it may be that the size won''t seem so huge, depending on where you are moving. I can relate to not wanting to change your parameters, but it might be good to be open to stones that are in the 1.5-1.7 range. You might could even go up in color or clarity if you did. The 1.63 that I sincerely hope to keep has the ultra tight specs mentioned here. The other stone I am looking at is an AGS0 but the variations are greater than some have preferred here. Yet the great thing is, I can see them both, which helps me learn what I like to SEE, and not whether I can tell which stones specs are tighter. I plan to report on this later today when the two diamonds come.

Storm, I hope you''ll drop in on my new thread later today to see my comments comparing two stones with different crown and pavilion variations. My hunch is that they''ll both be fabulous and I won''t be able to tell the difference. All this number talk is great, but the average consumer may or may not be able to tell the difference. We shall see!

 

[Paul-Antwerp]

Date: 7/12/2006 9:32:23 AM
Author: diamondseeker2006
You guys do nothing to help diamond OCD. It was bad enough having to look at crown and pavilion angles. Now you want us to look at the helium scans for crown and pavilion variation. I feel like a master''s in physics is required to pick out a diamond!

No need for a master in physics. You just need to know the brands that stand for something and/or the dealer/retailer who knows his stuff.

On a car, do you have any idea how Horse-Power is measured. I do not.

Live long,

 

[diamondseeker2006]

Lol! Well, I married someone who understands car engines, so that is one area I never have to think about! But like you said, I have had the privilege of working with great guys like Wink and Jonathan who know diamonds and I DO trust them!

 

[WinkHPD]

Date: 7/12/2006 9:44:42 AM
Author: diamondseeker2006
Lol! Well, I married someone who understands car engines, so that is one area I never have to think about! But like you said, I have had the privilege of working with great guys like Wink and Jonathan who know diamonds and I DO trust them!

Thank you for your kind words! It takes a LOT of work to keep up with the ever increasing body of knowledge available in the diamond world. Just about the time I get to think I am knowing something, then another mountain of information is released by AGS, GIA, or even by someone like Paul, who really does know a lot about the diamonds...

Wink

 

[Paul-Antwerp]

You know, the whole technical aspect becomes even more complicated in the area of fancy-shapes.

In princess-cuts, for instance, one cannot work with click-rings to fix the azimuth of the various facets, especially the chevron-facets. Even holding or fixing the stone in the tang is a more difficult task.

But in the end, the result is the same, the better the symmetry of the stone, the better the light performance.

Live long,

 

[delonn]

Experts,

Given the pavilion variances, is it fair to say that this stone will most likely exhibit great optical symmetry?

 

[delonn]

This one has lower pavilion variances but higher crown variance. Thoughts?

 

[Garry H (Cut Nut)]

http://www.gemology.ru/cut/english/symmetry/6.htm
This can explain why you need more information about the planes of the angle deviation to know about these stones.

Table tilt is common, as is a little dust under the table of the scanned stone - both can lead to wrong interpretations of the data you have given.

 

[Paul-Antwerp]

Date: 7/14/2006 8:25:25 PM
Author: delonn
Experts,

Given the pavilion variances, is it fair to say that this stone will most likely exhibit great optical symmetry?

Delonn,

neither stone comes close in tightness. On the first one, the difference in pavilion angle is rather high. The second one is better at that, but with the lowest one going down to 40.2, part of the pavilion is going over the edge.

Live long,