AGS New Cutting Guideline Charts for Princess Cuts

[Rhino]

Just arrived in the mail from AGS. I''ll check out the CD they sent with the info and share my input.

 

[Rhino]

First thing I love about it... a knowledge of all the primary facets are involved which means 2 sets of crown angles and 2 sets of pavilion angles. Something I''ve been saying for a long time already to get an accurate assessment according to the *numbers*. There are seperate charts for square princess cuts for tables of 55%, 60%, 65%, 70%, 75% & 80%. Each of the charts is organized very similar to Gary''s and MSU colored charts ... red indicating the highest brilliance possible.

 

[nicstn]

Some more info please. i have a princess w/a large table but the stone is absolutely beauitful. Much nicer then i though it would be by numbers alone. The old chart only rated my stone 3A mostly because of my large table 83%. Can you tell me what it said for tables of 80% please. It would be much appriecated. BTW love your doggie pic so cute.

 

[Rhino]

In the process of scanning them now. However to gain an accurate an accurate assessment we''d need to know primary and secondary crown angles as well as primary and secondary pavilion angles.

 

[nicstn]

here is the info on my EGL USA cert I''m not sure if this helps this is everything on my cert. thanks for the help.

Here are the specs
EGL USA Certificate
1.41ct
Rect. Mod. Brilliant
H
VS2
6.57 6.16 4.46
Depth 72.4
Table 83.0
Crown 5.7
Pavilion 63.3
Girdle thin to thick
Polish Good
Symmetry Good
Florescence none
Cutlet none

 

[Rhino]

Leonid... it does say copywrite across the graphics. Does this mean I can not post them here on the forum publicly?

 

[valeria101]

Jonathan.... how come I did not see this ? Perhaps some detailed description (but not the reproduction of the charts exactly) would do ?

 

[Hest88]

Ugh, if it''s copywrited you probably shouldn''t post the scan. But maybe you could just crop it and post the text?

 

[Garry H (Cut Nut)]

I have been told by Peter Yantzer that the information is for manufacturers use and is not to be published until they make appropriate press releases Rhino.

I think you should respect that.

Clearly princess cuts are very much more complex - it is the main reason I never attempted to do an HCA for fancies - it is beyond my capacity as a solo outfit.

I am certainly flattered that AGs have chosen to use my color scheme to present their information.

Sergey, Yuri and I still believe the "parametric" approcah to cut grading is inadequate because it locks the industry into cutting predetermined shapes. (Gabi Tolkowsky feels very strongly about this).
We see the time when a cutter can plan a rough diamond with an OctoNus scanner and create one off diamonds for whatever desire the fashion and markets of the day want.
Brilliance?
Fire?
Scintillation?

(edited to add that I think AGS is doing a great job and providing a much needed service)
Free form or structured shape?

 

[valeria101]

Date: 11/19/2004 5:29:36 PM
Author: Garry H (Cut Nut)

We see the time when a cutter can plan a rough diamond with an OctoNus scanner and create one off diamonds for whatever desire the fashion and markets of the day want.
Brilliance?
Fire?
Scintillation?

Garry, does the OctoNus software optimize optics of free form cuts ????????????????????????????????????????????????

Anyway.

I would mark the "Pricescope Day" right after Thanksgiving in every eyar''s calendar, if you could add a small page of what can be achieved with such one off models. (say, a one page description of the design and optics optimization process - all at a glance). It is the one fundamental bit missing in PS''s vast and erudite literature. And it is much missed, as far as I can tell.

 

[lovesquares]

About when do you think this info will be made public? It it safe to assume that the princess diamonds on the market presently will have to be re-priced and re-evaluated against the new guidelines?

 

[JohnQuixote]

Date: 11/19/2004 5:29:36 PM
Author: Garry H (Cut Nut)
I have been told by Peter Yantzer that the information is for manufacturers use and is not to be published until they make appropriate press releases Rhino.

I think you should respect that.

Clearly princess cuts are very much more complex - it is the main reason I never attempted to do an HCA for fancies - it is beyond my capacity as a solo outfit.

I am certainly flattered that AGs have chosen to use my color scheme to present their information.

Sergey, Yuri and I still believe the 'parametric' approcah to cut grading is inadequate because it locks the industry into cutting predetermined shapes. (Gabi Tolkowsky feels very strongly about this).
We see the time when a cutter can plan a rough diamond with an OctoNus scanner and create one off diamonds for whatever desire the fashion and markets of the day want.
Brilliance?
Fire?
Scintillation?

(edited to add that I think AGS is doing a great job and providing a much needed service)
Free form or structured shape?

Garry, to your knowledge (if you can comment), does the new system take into account obscuration and contrast brilliance as discussed at IDCC?

 

[Rhino]

Hey Sir John,

I don''t believe head obstruction is any kind of a problem in princess cuts. At least not in most of the stones I''ve seen. Regarding the aspects the reduce contrast the major problem in princess cuts is generally not too much obscuration (spelling?) but that of leakage. Most princess cuts leak live sieves and those that do return light well do not do it at a high enough intensity. These have been my observations.

 

[Garry H (Cut Nut)]

I agree with Rhino - but yes - they will use the same approach - the ASET scope will show more green in the returned light.

 

[JohnQuixote]

RhinoKnight...Yassir, I know'd it

I should have been more specific - I'm curious about both systems.

Garry, with angular spectrum G still = rays arriving from H to 45 degrees? Both systems?

 

[Garry H (Cut Nut)]

John were you drinking when you posted this - not sure if you were doing a Star Trek joke - or being serious?

Rhino I posted this on another thread - but in case you did not see it -
(Only DiamCalc users will fully understand this)
The new AGS princess charts are guidelines for manufacturers. AGS modeled diamonds in DiamCalc with complex chevron H1, H2, H3 relationships. Remeber there are two different pavilion angles - the 4 triangular shaped facets that do not affect the depth, and the diagonals that affect the pavilion depth. Crown angles are somewhat similar, although not as critical.

They modeled hundreds of thousands of square princesses to get high and low values. Also, the charts are only for princess cuts with 2 rows of ''chevron'' facets on the pavilion. They are currently modeling 3 and 4 chevron row variations (which personally I think are only valid for larger stones). In their new system, all of the facets will matter because they will use a very accourate ray trace a 3D scan of the stone. If a manufacturer cuts normally, without indexing any facets, the guidelines should be very accurate.

So if there are some unusual combinations of proportions that are outside AGA guidelines - it may not be a surprise.

BTW what they have done is similar to the basis of HCA (for which I have recieved endless criticsm) - but far more complex because princess have more crown and pavilion angles.

this is

 

[Garry H (Cut Nut)]

This might help explain the Chevrons and pavilion angles?

 

[Garry H (Cut Nut)]

.

 

[Garry H (Cut Nut)]

And here is the difference in appearance between a stone with 4 vs 2 chevrons.
Above 1 or 2ct a larger number of chevrons is good, but below 1.2ct 2 is plenty.

 

[valeria101]

Why do diamonds with lots of small facets (brilliant style) score better on the GA than the large-facet counterparts (steps) ?

Is this just silly illusion from my part or there is indeed some underlying bias?

Just happened to remember seein the princess faceting above

The observation that more facets benefit larger diamonds seems common - even got branded. I am trying to understand on what this relies technically.

 

[Serg]

re: "The greatest experts are only as good as the sum total of what they have seen." [Souren Melikian]

I am disagree again.
Expert is not database only.
Expert could produce new knowledge using the sum total of what he has seen.

 

[strmrdr]

Date: 11/21/2004 8:44:37 AM
Author: valeria101
Why do diamonds with lots of small facets (brilliant style) score better on the GA than the large-facet counterparts (steps) ?


Is this just silly illusion from my part or there is indeed some underlying bias?


Just happened to remember seein the princess faceting above

The observation that more facets benefit larger diamonds seems common - even got branded. I am trying to understand on what this relies technically.

Im going to give my theory on it and Gary H can tell me im all wrong
This is easier to see in colored stones than diamonds from what Iv seen but does it in both.

Facet junctions and near facet junction tend to break up light into smaller visible flashes and send them out in more directions.
This is verified by ray tracing but Iv yet to see the experts comment on it when Iv presented it.

The smaller more scattered flashes have a better chance of reaching the viewers eyes than fewer large flashes going out in only a few directions.
The angle of return on a smaller stone tend to be tighter than on a larger stone there for the more scattered light output helps large stones more.
Also the larger stone collects more light so the smaller flashes can be brighter and there are more of them.

Now another related thing that comes into play in large stones is that you get larger reflectors that seem to get more directional and if they arent returning at the proper angle you will never see them.
More facets = more angles of return and the better chance of some of those beams hitting your eyes.

Take a mirror and set it like this \ and look straight in it you wont see a lot of light return because the light is being reflected away from you by the directional nature of the return. Same with large diamond reflectors.

So in conclusion add up the more facet junctions and its scatter combined with more angles of return and you can see why they might look better to some people and more so in the larger sizes.

 

[strmrdr]

rough drawing of the mirror setup.

 

[Serg]

Date: 11/21/2004 10:40

8 AM
Author: strmrdr
rough drawing of the mirror setup.

It is wrong draft.

Light will go to eye always if mirror is big enough.

Mirror is big enough on your draft.

 

[Garry H (Cut Nut)]

the other factor Storm is that if the facets get too small we can not resolve the light that is returned. Then it just looks blah - bright but blah.

 

[valeria101]

Date: 11/21/2004 6:39:55 PM
Author: Garry H (Cut Nut)

bright but blah.

My thoughts exactly !

 

[Rhino]

I follow Strms reasoning and concur as I have stones like this I work with daily. I don''t understand "bright but blah"? IMO, leakage = blah ... too much head obstruction = blah ...

When I look into the face of a diamond and I see *brightness* ... isn''t this what we''re looking for? Granted ... different cuts and variations in the optical design are going to alter how that *brightness* is being reflected back to the eye but I''d take a hella bright diamond ANYDAY over a leaker.

Strm... with the new 2nd generation super ideals we''ve been working with I am finding this to be exactlyl the case. More mirrors = more reflections of light so long as the facets are functioning as mirrors and not windows.

 

[strmrdr]

Date: 11/21/2004 6:39:55 PM
Author: Garry H (Cut Nut)
the other factor Storm is that if the facets get too small we can not resolve the light that is returned. Then it just looks blah - bright but blah.

thats one reason it works better with bigger diamonds.
Iv looked at some star129 diamonds the smaller ones look bright but kinda wierd.
The 2ct I looked at was better in that regard but I liked the h&a ideal cut look better.

 

[Garry H (Cut Nut)]

thanks Storm
Rhino - like a .005ct single cut looks better than a .005ct 57 facet stone

 

[valeria101]

Not that I am very sure of what I am talking about... but isn't the "blah" lack of scintillation?

There is an open statement left in the new Ideal-Scope.com about how the Ideal-Scope and B-SCope readings relate:

"Scintillation - we are not sure what this is a measure of [on the Brilliance Scope scale]. We think that some darkness evenly distributed in the Ideal-Scope image helps raise the score. We welcome any advice or help." (cited from here)

Sounds interesting. The white and red on the Ideal Scope are 'easy' - the more/less the better. But black (reflectors, contrast brilliance or whatever other name is used) is supposed to be there with some moderation. Until now - as far as I remember - it remains anyone's guess what "moderation" means.

Worth talking about ?