AGS New Round Stone Cut Grade System for 2005

[Garry H (Cut Nut)]

This is a chart from the Rapaort story.
Someone put a link up please?

Rather like my guess from the other thread that got hijacked by Marty

 

[Garry H (Cut Nut)]

My best guess one month ago

 

[adamasgem]

----------------
On 10/11/2004 10:22:18 PM Garry H (Cut Nut) wrote:

This is a chart from the Rapaort story.
Someone put a link up please?

Rather like my guess from the other thread that got hijacked by Marty----------------

As I said before, while AGS has "released" their charts, they don't say anything about the "environment" used to make the charts. I got a ppt copy of the AGS presentation which showed these expanded grade ranges, but one can generate "new grades" for just about any environment one choses to, and the "answers" will all be different.

GIA is the only one to adequately define so far the environments used in their studies, whether or not one agrees with the use of that specific lighting environment to characterise which cut is "best".

GIA used hemispherical lighting for WLR and a parallel beam for DCLR, but my uinderstanding is that they will define a new environment in the upcoming G&G. MSU said, if I remember correctly (please correct me on this if I am wrong), they used a uniform background, plus 4 or 5 "spots", but didn't define the placement of the spots, which will effect and possibly alias any result.

GIA, quite properly, in my opinion, used a cosine squared weight function to take into account the variation caused by the viewer rocking the stone, while AGS apparently is using two fixed viewer aspect angles, 0 and 15 degrees, but I haven't been able to find out what the lighting lighting with respect to the table of the stone.

Backwards photorealistic raytracing assumes a viewer with a fixed FOV. I don't believe that is the way to go.
I happen to like the GIA weighting approach considering which tries to consider a weighted viewing from all aspects of the stone, the top view being the most highly weighted.

All these efforts involve immense computational resources to do the job "properly".

I haven't seen a one to one comparison of true monte-carlo and backwards ray tracing published, so I can't comment on the validity. I'm trying to resolve some issues with Serg regarding our technical differences, but we are getting there.

 

[Garry H (Cut Nut)]

marty have you ordered your copy of the Diamond Cut conference proceedings yet from ideal-scope front page?

They have described quite a lot there

 

[Rhino]

Hi Gary,




I haven't read or seen the chart just yet. That's my first time seeing it though I heard about it's release during the NY JCK show. Quick question... does it basically correlate with HCA regarding proportion data? If not where does it differ?

 

[strmrdr]

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On 10/12/2004 10:26:50 AM Rhino wrote:



Hi Gary,



Quick question... does it basically correlate with HCA regarding proportion data? If not where does it differ?

----------------[/quote]

gmta I was just going to ask the same question.
Is it really new or just what we have been using all along with the hca?
Whats the worst case hca and the best case hca score for the new ags 0?

 

[Lynn B]

Garry,

THANKS so much for sharing. Verrrrry interesting...

So with their graph skipping every other number, how do you figure out one like mine, (34.8/40.9)? Thanks,

Lynn

 

[Lynn B]

And what is the purple? The old guidelines?

Thanks!
Lynn

 

[Garry H (Cut Nut)]

The purple is the old AGS 0.

Rhino my HCA goes shallower than AGS for the following reasons:

1. I include a penalty for spread - so a tolkowsky stone gets about 0.5 penalty for example, where as a stone at the lower left end of the AGS old purple gets 0.1 HCA spread penalty.

2. AGS assume a closest viewer is at 250cm (10 inches). I assume 16 inches, so the shallow stones I accept will look dark from really close up. It is semantics. Different line in sand.

Otherwise I find it very flattering that they agree with my hard work and low expendeture (about 10x$10 bottles of wine)

 

[Rhino]

Very interesting mate. Just curious ... we can account for this head obstruction in DiamCalc too right? So in AGS's grading they're using a 10" distance from viewer to diamond head obstruction standard.

 

[Garry H (Cut Nut)]

Rhino this is a model of an 8* as seen from 16 inches and on the right from 10 inches modeled in jewellery store lighting.

As i said, I think 10 inches is too close for all but under 20 year olds.
AGS chose 250cm because it is some sort of US military standard.

 

[Rhino]

Gotcha... shorter distance = greater head obstruction. longer distance = less head obstruction.

 

[Rhino]

Just broke out the slide ruler. I would have to side with a 16-17" observation as opposed to a 10". An average sized adult it seems would also fall into this norm. I'm 5'11", 190lb with an average build.

 

[Garry H (Cut Nut)]

Rhino you are larger than you are in real life.

I would say 6' 11" and 250lb would be neare the mark

 

[Garry H (Cut Nut)]

Does this help visualize the two systems?
AGS 0 55% table candidates from the Rapaport magazine article, overlain on HCA 55% table chart including HCA spread reduction that favors shallower stones

 

[Garry H (Cut Nut)]

Here is an update - the same chart as before with the AGS white zigzagbox (hard to see in places) and an earlier GIA chart (May 2004) with a couple of confirmed stones with nearly the same sized tables marked in black. Hope it makes sense.
Leonid and I are redoing the PS tutorial with this new info in mind.

In general, you can probably use HCA to tell if a stone is too steep / deep, but HCA accepts shallower stones.

Hope this is useful.

 

[Garry H (Cut Nut)]

trying a different image again

 

[valeria101]

Date: 11/2/2004 11

5

7 PM
Author: Garry H (Cut Nut)

Leonid and I are redoing the PS tutorial with this new info in mind.

Would it be possible to put other lab standards on the chart (or a version of it) as well ? Say, EGL, HRD, AGA... whoever else uses compatible standards.

A recent post gave this idea. And there were countless asking about how come some diamonds are "more ideal" than others.

 

[valeria101]

These two came from Garry of course:

 

[valeria101]

 

[Garry H (Cut Nut)]

Thanks Ana

The first chart:
Here is an update - the same chart as before with the AGS white zigzagbox (hard to see in places) and an earlier GIA chart (May 2004) superimposed over the top - with a few confirmed GIA stones with nearly the same sized tables marked in black. Hope it makes sense.
Leonid and I are redoing the PS tutorial with this new info in mind.

In general, you can probably use HCA to tell if a stone is too steep / deep, but HCA accepts shallower stones than probably either new system.

The second chart shows the old and new AGS for 55% table sizes - with Ideal-Scope images of the old and the new overlain.

Ana there is an example of AGA as well at the start of this thread. It is probably not much use to compare to HRD and others because they are so broad they are useless as selection criteria.

 

[valeria101]

Date: 11/3/2004 2:18:39 AM
Author: Garry H (Cut Nut)

In general, you can probably use HCA to tell if a stone is too steep / deep, but HCA accepts shallower stones than probably either new system.

Trying to understand... again:

In your sentence,"'steep and deep" relative to any and every system - the HCA is in acord with them there (= there is no red to the right of the AGS box).
Why are shallower stones (with both flatter pavilion and flatter crown than the AGS box) accepted? How do these look ? There hardly was any to talk about around here in about a year by now.

 

[Garry H (Cut Nut)]

Ana I have explained this in the middle of this thread with Rhino.
I also posted this image before (pray that it works).
I have modelled the same stone - slightly shallow - that would not get AGS 0 - but gets a good HCA score - so that you can see the difference between a very close up viewers head obstructing light.
Look at the areas underlined in RED

 

[oldminer]

AGS ran a web based seminar yesterday, today and wilkl run it again tomorrow on their new cut grade system. I registered for it today and listened in. It was very informative and a little unrehearsed. Pete Yantzer did an excellent job of giving non-technical information on the proposed system. It will rely heavily on software with many details of facet lenght relationships figured in, not just the simple parameters. If oen has access to the software and the Sarin, it will be easy enough, but we will not be able to say which stones qualify until they are fully examined. We will be more able to say which diamond are candidates for AGS 0, but the final grade will be heavily technical.

Two problems:

1. The system relies on a 3D model based on Sarin. It is not sufficiently accurate. Maybe they will buy the Helium devices, but I doubt this is ready yet. I don't know. Garry, is it ready? Does AGS have it already?

2. The system is ray trace based. What will it do on a diamond that is a bit or more than a bit cloudy? It is a predictive system, not a direct reading system.

A third problem is how they arrived at the arbitrary choices that were made for tilting and light model. I know one must make choices, but are they sound choices? Will there be better proposals? Will this become a standard?

Anyway, it is an exciting time for diamonds and those with an interest in them.

 

[Garry H (Cut Nut)]

The times are a bit tricky for me Dave - but when is the next one - how many hours from now?

What format was the information given in?
Did you see more than the 55% chart that was published in Rapaport?
Did you see the charts for candidates 47% through to 61% ?

It is great that AGS are going to measure girdle thickness at the thickest part - no more girdle cheating (gouging) and it means that the same system will be used for all different shapes.

Re Helium - Sergey is travelling in Asia at present and I think it more appropriate that he answers the comments re Labs buying Helium. But I can say that the product is available and there have been 2 deliveries in USA and there are likely to be more.

Was this image one that was shown?

 

[Garry H (Cut Nut)]

Just saw something on another bullitin board posted by a cutter who we might expect to be knowledgable. This is what he wrote:

"New AGS Cut Grading System: What Happens When...?
The new AGS Cut Grading System increases and significantly broadens the range of AGS-0 designated diamonds by 37%!

What happens when a consumer who has purchased either an AGS-1 or AGS-2 diamond under the old system puts in a claim with their Insurance Co. because the stone has been either lost or stolen.

Will the insurance company reimburse under the old grading system (AGS-1 or AGS-2) or pay under the new system whereby this diamond has now become an AGS-0 and is selling at a higher market price?

Conversely, owners of AGS-0 diamonds under the old AGS cut grading system will no doubt be very unhappy to see the value of their diamond(s) diluted and decreased under the new Cut Grading System.

rbrilliant, denverappraiser; your comments?"

This shows how little is understood, and how much learning will be required for many in the industry. The AGS range IS broader, but it IS ALSO narrower and more effective at predicting diamonds with proportions that make for great looking diamonds.

There are very few AGS 1''s and 2''s anyway - and some are still going to be rulled out for symmetry, polish, spread etc etc

And the number of AGS higher #''s that will fall within the new AGS 0 will be rather small as a % of the possabilities.

And with regard AGS 0''s that no-longer make it - you will see that there are very few that PRicescopers would have bought because they would get lousy HCA scores anyway

 

[Lynn B]

Garry,

Thanks for all the great information. Very interesting.

It seems like my stone (AGS 0; 1.53 carat; Table: 56%; Depth: 60.7; Crown: 34.8; Pavilion: 40.9) is right "on the edge" of the new AGS 0 range. What would that mean, under the new grading system? Still an AGS 0?

Thanks,

Lynn

 

[sixstrrzr]

Hope I''m not missplacing myself here, but should all these charts & graphs mean anything to me, a newbie 1st-time buyer?

I am somewhat well-versed in stereo/audiophile equipment, and I used to get asked all the time "what should I buy"...to which I replied "ignore THD percentages, Fletcher-Munson curves, 2-way vs. 3- and 4-way speakers. Go down to the store & LISTEN to it!. If it sounds good to you, buy it".

Should I not get bogged down in color charts, and base my purchase on an appraised rock that looks good to me?

 

[Garry H (Cut Nut)]

What the charts mean is that the stone with those proportions (LynnB) will be candidates for AGS 0.

If the lower girdles and girdle thickness sym and polish are all in line too - then yes - it will still be an AGS 0.

Sixstrrz you might like to read the tutorial for a better understanding

- it is under knowledge on top tool bar.

 

[Lynn B]

Garry,

Thanks for the reply. I appreciate it!

Lynn