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Help with the cut quality on a diamond

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Garry H (Cut Nut)

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Very good question????

Either the stone has been ''dug or painted'' (brillianteering issues in GIA jargon), but they add a comment when that is the case - and this stone has no comment warning??????

The proportions are within GIA''s Excellent proportions.

So my guess is GIA messed up.

Ask BN?
 

stebbo

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Combo of being a bit deep and a bit fat around the waist giving a poor spread my bet. GIA will knock down an EX if the spread is 5% or more (-ve and +ve).
 

hedarud

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Thank you both, it is interesting, plugging the numbers into the GIA cut estimator gives VG also.
 

Garry H (Cut Nut)

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Date: 9/5/2007 10:53:52 AM
Author: hedarud
Thank you both, it is interesting, plugging the numbers into the GIA cut estimator gives VG also.
It should not as per GIA''s own rules.

The probable reason is that the girdle is being measured as Thick by the Sarin scanner, but this is incorrect as GIA have told John Pollard and I that they do not make their girdle thickness calls based on the scanner output.

They have called the girdle Medium to slightly thick on the report.

However if as you did - you enter the data in the scan info into Facetware - it shows VG. Drop the depth 62% back to 61.9% and the girdle data gets that tiny bit thinner and the stone becomes excellent.

The spread is no where near the -8% which we commonly see as the cut off point It is -4% compared to tolkowsky.


So this stone is likely to be a bargain because of what appears to be a glitch in the implimentation of GIA''s own methodology.
 

stebbo

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Date: 9/5/2007 4:26:16 PM
Author: Garry H (Cut Nut)
It should not as per GIA's own rules.


The probable reason is that the girdle is being measured as Thick by the Sarin scanner, but this is incorrect as GIA have told John Pollard and I that they do not make their girdle thickness calls based on the scanner output.


They have called the girdle Medium to slightly thick on the report.


However if as you did - you enter the data in the scan info into Facetware - it shows VG. Drop the depth 62% back to 61.9% and the girdle data gets that tiny bit thinner and the stone becomes excellent.


The spread is no where near the -8% which we commonly see as the cut off point It is -4% compared to tolkowsky.


So this stone is likely to be a bargain because of what appears to be a glitch in the implimentation of GIA's own methodology.

Facetware's VG result was based on a slightly thick girdle being entered, not a thick. Even if Facetware didn't use the entered value but calculated it, it could conclude nothing else than that it is slightly thick, as DiamCalc would show (and it's not borderline either).

DiamCalc also concurs and gives it a VG. It penalizes when AGSSpread exceeds +/- 5% and this stone has an AGSSpread of -5.8%. Dropping the depth like you suggested will simply bring the AGSSpread back within 5%. I agree it'll likely be a bargain, but because it's borderline, not because of a glitch.
 

JohnQuixote

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This stone is a victim of rounding.Rounding I tell you.

41.0/34.5 and 40.8/35.0 would both receive EX so if this innocent diamond has been rounded from an actual of 40.9/34.7 (spread -4%) the software may be unfairly penalizing it.On the other hand, rounding it from 40.7/34.7 would deliver the same result while rounding it from 40.7/34.3 makes it look better than it is.

Doesn't change appearance a bit, but it makes us OCD types crazy.
 

Garry H (Cut Nut)

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Date: 9/6/2007 1:35:12 AM
Author: JohnQuixote

This stone is a victim of rounding.Rounding I tell you.

41.0/34.5 and 40.8/35.0 would both receive EX so if this innocent diamond has been rounded from an actual of 40.9/34.7 (spread -4%) the software may be unfairly penalizing it.On the other hand, rounding it from 40.7/34.7 would deliver the same result while rounding it from 40.7/34.3 makes it look better than it is.

Doesn''t change appearance a bit, but it makes us OCD types crazy.
Rounding smounding

Rounding like our respective girths Dear Knight of the order of St John.
39.gif


Its all in the girdle - remeber the words of Phil Yantzer in Vegas last year?
 

stebbo

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Any idea Garry why Sergey won't assign a GIA 2006 EX if the AGSSpread is more than +/- 5%?

Appraise.txt

GIA_PCT_2006 Appraiser
[cut]
Name: Brilliant
Quality: E V G F P
Parameters: \
GirdleHeightBzlMin (%) \
GirdleHeightBzlMax (%) \
Culet_mm (s) \
SpreadAGS (%)
Mass: 0.00 100000.0 \
0.50 5.00 0.50 5.00 Pointed Medium -5 5 \
0.01 5.00 0.01 5.00 Pointed "Slightly large" -10 10 \
0.00 6.00 0.00 6.00 Pointed Large -15 15 \
0.00 7.00 0.00 7.00 Pointed "Very large" -20 20 \
0.00 8.00 0.00 8.00 Pointed "Very large" -20 20
 

Garry H (Cut Nut)

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Date: 9/6/2007 11:15:40 AM
Author: stebbo

Any idea Garry why Sergey won''t assign a GIA 2006 EX if the AGSSpread is more than +/- 5%?

Appraise.txt

GIA_PCT_2006 Appraiser
[cut]
Name: Brilliant
Quality: E V G F P
Parameters:
GirdleHeightBzlMin (%)
GirdleHeightBzlMax (%)
Culet_mm (s)
SpreadAGS (%)
Mass: 0.00 100000.0
0.50 5.00 0.50 5.00 Pointed Medium -5 5
0.01 5.00 0.01 5.00 Pointed ''Slightly large'' -10 10
0.00 6.00 0.00 6.00 Pointed Large -15 15
0.00 7.00 0.00 7.00 Pointed ''Very large'' -20 20
0.00 8.00 0.00 8.00 Pointed ''Very large'' -20 20
I think it is just for convenience - using the AGS rules because they have been clearly defined.
GIA has not clearly defined their rules Stebbo

(BTW - I do not fully understand the software method - i am the diamond man, not the computer man)
 

stebbo

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Date: 9/7/2007 1:41:13 AM
Author: Garry H (Cut Nut)
I think it is just for convenience - using the AGS rules because they have been clearly defined.

GIA has not clearly defined their rules Stebbo
The AGS2005 rules in DiamCalc are different again, only penalizing excessive -ve spreads, not +ve and -ve like the GIA2006 does, so it does look intentional, not just for convenience. Are you sure the boys at Octonus don't know something yet to be clearly defined?

I can understand that the stone might be a victim of rounding and may have deserved an EX, but that doesn't explain why those otherwise good looking rounded proportions consistently pull a VG when graded, in Facetware and in DiamCalc.
 
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