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AGS and GIA: Cut Comparison Charts

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JohnQuixote

JohnQuixote

Ideal_Rock
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Each lab's system can be evaluated on its own merits. Nevertheless, comparisons will be unavoidable.

GIA EX has proportions combinations outside of AGS Ideal.
AGS Ideal has proportions combinations outside of GIA EX.
They have overlapping combinations in common.
Treating each ‘box’ separately I totaled the numbers.

This thread is intended to help those wishing to identify, on a broad scale, what AGS and GIA see in common and what they do not.

Note that this is a rough proportions overview. Minor facets (GIA), depth/girdle judgments (both labs) and actual light performance (AGS) influence final grades. Thanks to Martin Haske for originally posting the charts.

AGSGIARatios.jpg
 
What I find interesting is that my favorite combos are blue on the chart, the ones that they both agree on.
If you took all of the diamonds recomended in the last year on pricscope im think the vast majority of them would be in the blue on those charts.

To be honest both systems leave off diamonds I like or include some I dont.
Neither to me is the final word on well cut diamonds.
 
I would want the vendor to be able to honestly tell me where the diamond would fall in BOTH systems, and WHY.....
2.gif
 
looking over them I just noticed something 40.8 34 block should be blue for tables between 54 and 58
They are AGS0 new system
 
Is there something that can be done to make sure this thread is easy to access????
 
Date: 3/12/2006 7:52:05 PM
Author: Carlotta
Is there something that can be done to make sure this thread is easy to access????
Click to expand...
we can move it into FAQ later
 
THANKS!!
emwink.gif
 
Interesting info John. Considering GIA is a 5 grade system and AGS is an 11 grade system the numbers come at no surprise. Thanks for posting that.
 
Date: 3/12/2006 11:30:17 PM
Author: Rhino
Interesting info John. Considering GIA is a 5 grade system and AGS is an 11 grade system the numbers come at no surprise. Thanks for posting that.
Click to expand...
One might also take the buyer''s perspective that the AGS Ideal range is a lot tighter than GIA''s EX.

While both labs have opened up the "combinations" they feel rank at the top, what has been added is that, at least for AGS, they are considered in combination and not the square, non correlated boxes of the past, which we all knew was a problem. In the past we would only consider 24 total boxes as in the GIA Cut class 1, let alone consider boxes with symmetry ranking only VG as being an EX cut.

While these data alone are a crude approximation, it does appear to show the GIA''s bullseye is much LARGER than AGS''s.

Someone could take the time to see how many AGS 1''s, 2''s and 3''s are considered GIA EX

Are we being asked by GIA to consider a Ferrari equal to a Chevy.
 
Date: 3/12/2006 7:11:28 PM
Author: strmrdr
looking over them I just noticed something 40.8 34 block should be blue for tables between 54 and 58

They are AGS0 new system
Click to expand...
Appreciate it Strm. I corrected the graphics and data. Thanks to Leonid for reposting them.

AGS has an 11 level system. GIA has 5 levels.

Using the above EX/Ideal comparison charts I pulled some graphics for the top grades only. Across the 10 charts are a total of 544 proportions combinations allowed in EX and/or Ideal. Combos span CA 31.5-37 in .5 increments / PA 40.2-41.8 in .2 increments / T 52-62 in 1% increments.

Of the 544 combinations:

GIA EX only = 435
In Common = 80
AGS Ideal only = 29
(Pie Chart)

GIA EX total: only+common = 515
AGS Ideal total: only+common = 109
(Bar Graph)

AGSGIACharts-Numbers.jpg
 
Date: 3/12/2006 11:30:17 PM
Author: Rhino
Interesting info John. Considering GIA is a 5 grade system and AGS is an 11 grade system the numbers come at no surprise. Thanks for posting that.
Click to expand...
Hadn''t noticed your post before, but I think you should RE-THINK your analysis about it being no surprise, or go back to school nd learn some arithmatic.

This is unless of course that you realize how overly wide the GIA paradigm is, DISPROPORTIONATELY, and that GIA EX''s will include AGS 0,1''s,2''s,3''s and 4''s and given the polish issue the spread may be even wider. (I agree with GIA on VG and EX polish still in the top grade, but I disagree with the SEVERE opening up of the EX top grade)
 
Try again - from Peter Yantzer - in GIA's format (why did they do that?)

A comparison of the 57% table size charts shows that GIA Excellent proportions (outlined roughly in black) had only 26 good and 31 bad matches between AGS0 and AGS1. Included in these bad matches were several very bad matches: 7 AGS 5 & 4 AGS 6’s that would be graded Excellent by GIA. This is a poor match and confusing for both consumers and the industry. The situation is worse for table sizes below 52% where GIA has no Excellent proportion sets. For example at the 51% table size AGS has 17 AGS0 and 22 AGS1 ‘candidate’ proportion sets that GIA would grade as Very Good, Good or Fair.

AGS 57ChartSma.jpg
 
Still, if though not too helpful for the larger population not schooled on HCA, if you consider the radical change with GIA is for them to have included their crown & pavilion angles, even though it is rounded data, you can still apply this info at will, use the data they now provide, and come away with an educated guess about how favorable your option will be...

Certainly, per HCA protocol, a better initial sort than GIA excellent would otherwise give you.
 
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