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what are the cons on a shallow/shallow cut rb?

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Dancing Fire

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JP...can you please post some IS and ASET pic. how shallow/shallow can a stone be and still receive a GIA XXX ? how about for AGS ideals ?
 

John P

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Date: 2/20/2009 2:21:05 PM
Author:Dancing Fire
JP...can you please post some IS and ASET pic. how shallow/shallow can a stone be and still receive a GIA XXX ? how about for AGS ideals ?
GIA doesn't allow bad shallow combinations. Nothing under 40.6 PA can earn EX and the shallowest combo is 40.6/34.0 in tables up to 59%. Nothing under 40.8 PA can earn EX for tables 60-62%. Diamonds at the shallow side of GIA EX are usually very nice.

AGS applies a 3D system which is diamond-specific, so there are not guaranteed numbers. They produce cut guides which predict 40.2 PA can earn Ideal if paired with 36-37 CA (small tables) and 40.6 PA can earn Ideal LP if paired with 33.5-34.5 CA (60-62% tables) but an diamond will be assessed individually using angular spectrum/ray-tracing.

It bothers cutters that AGS table-crown-pavilion guides are not a guarantee. Cut consistency, minor facets and brillianteering can make or break the prediction and cutters don't like uncertainty; color and clarity are subjective enough. As a result its rare to find AGS Ideal configurations that have 'strayed' beyond the conventional near-Tolk makes (though some are out there).


Specfic to your question, the HCA shows basic overlap of GIA EX proportions to AGS Ideal candidates for each table size.

Here's 56



Here's 60



The pavilion angle is what many consider the most critical element and in the most popular metrics discussed here (AGS, GIA, HCA and AGA) pavilion angles 40.6-41.0 have the greatest approval cross-system.

There are exceptions but that range is a good starting place for discussion.

* AGS shows most 0 light performance candidates in that range.
* The HCA and AGA prefer the shallow side (and a bit lower).
* GIA prefers the steeper side (and higher)... If you were wondering, this is why the GIA gives EX to steep diamonds the HCA rejects and the HCA gives thumbs-up to shallow diamonds the GIA system doesn't reward.

I can roll out some simulations later, or someone else may be on it.

CONS

Basically the cons of shallow diamonds are that they can become subject to too much obstruction (aka obscuration, head shadow, blue in ASET, black in IS) and appear dark, especially when viewed close-up.
 

Dancing Fire

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the shallowest combo is 40.6/34.0 in tables up to 59%....

hey JP
can you please calculate an image using the above specs?

thanks
 

Rhino

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A 34.0/40.6 is a combo I would most definitely want to see before giving a thumbs up on it. Minor facet constrcution can make or break this combo.
 
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