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HCA question

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SecretMike

Rough_Rock
Joined
Nov 28, 2009
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The Halloway Cut Adviser has a white area that is AGS Ideal at this url:
https://www.pricescope.com/cutadviser.asp

However this ring on blue diamond has AGS Ideal 0 on the certificate and its not in the white outline...
http://www.bluenile.com/round-diamond-1-carat-signature-ideal-cut-h-color-vvs1-clarity_LD01394065

Also if you look at that diamond there is an AGSL and GCAL inspections and the numbers on depth/table/crown%/pavillion% do not match.
Is that common? That stuff seems like it should not be subjective
 

stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
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14,083
AGS outline in the HCA is just the cutter''s guideline, cased on average 2D proportions. AGS0 performance cut grading is based on the actual 3D proportion of the stone''s simulated light performance. You can get a AGS0 cut grade with average proportions lying outside the cutter''s guideline if all the facets work well with each other or not get a AGS0 cut grade even with the average proportions lying within the guideline if the individual facets do not work well with each other.

Difference in proportions measured can be due to error in calibrations of the equipment, quite common.
 

BobR

Shiny_Rock
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Oct 27, 2009
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105
SC
I also note a stone that falls outside the HCA white area (scoring 3.1) and yet per Octonus AGS tables scores Ideal on the Gold (2 dimension) table and 0 on the PGS (3 d guidelines?). Could it be that AGS 2 dimension grades have changed since HCA was developed??
Its GIA rpt no 2101387995, 0.73ct

Tried to upload the HCA for this but it failed for some reason, but if you run it for the following parms
Depth 62.0
Table 57
CA 34.0
PA 41.2!

Bob
 

stone-cold11

Super_Ideal_Rock
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Sep 9, 2008
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14,083
The gold proportion is a 2D based cut grade that has no relationship to 3D proportion based grading.
 

BobR

Shiny_Rock
Joined
Oct 27, 2009
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105
Date: 12/7/2009 3:37:40 AM
Author: Stone-cold11
AGS outline in the HCA is just the cutter''s guideline, cased on average 2D proportions. AGS0 performance cut grading is based on the actual 3D proportion of the stone''s simulated light performance. You can get a AGS0 cut grade with average proportions lying outside the cutter''s guideline if all the facets work well with each other or not get a AGS0 cut grade even with the average proportions lying within the guideline if the individual facets do not work well with each other.

Difference in proportions measured can be due to error in calibrations of the equipment, quite common.
SC, I''m still confused.
Not sure what you mean by cutters guidelines? ( Who has defined the guidelines - If AGS then why the difference on the stone I quoted?).
As you say, and what I understand for other threads, AGS Gold is 2d predictive model (similar to GIA) so as HCA is also 2d predictive model why the discrepancy with Octonus AGS gold tables??
 

stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
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14,083
Date: 12/7/2009 6:39:32 AM
Author: BobR
Date: 12/7/2009 3:37:40 AM

Author: Stone-cold11

AGS outline in the HCA is just the cutter''s guideline, cased on average 2D proportions. AGS0 performance cut grading is based on the actual 3D proportion of the stone''s simulated light performance. You can get a AGS0 cut grade with average proportions lying outside the cutter''s guideline if all the facets work well with each other or not get a AGS0 cut grade even with the average proportions lying within the guideline if the individual facets do not work well with each other.

Difference in proportions measured can be due to error in calibrations of the equipment, quite common.
SC, I''m still confused.

Not sure what you mean by cutters guidelines? ( Who has defined the guidelines - If AGS then why the difference on the stone I quoted?).

As you say, and what I understand for other threads, AGS Gold is 2d predictive model (similar to GIA) so as HCA is also 2d predictive model why the discrepancy with Octonus AGS gold tables??
AGS0 cutter''s guideline is given out by AGS after the introduction of the AGS0 performance based cut grades as the cutters are unsure of what proportions to cut to get the AGS0 cut grade. It is a guideline only, average 2D numbers, 3D performance based grading does not average the numbers. HCA plots the AGS0 guideline, not the gold guideline.
 

BobR

Shiny_Rock
Joined
Oct 27, 2009
Messages
105
Thanks for clarification SC
 
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