GIA facetware cut question

[Rman222]

Hi,
I have been fooling around with the GIA facetware available on their website. In playing with some diamonds posted on pricescope vendor websites it seems that more than a few of what I thought would be considered "super ideals" would fall into GIA''s "very good" category instead of excellent. I did not have the star and lower half percents of course from the available information, but trying many combinations of those still led to a "very good" classification. Am I missing something or doing something incorrectly or is the GIA "excellent" for cut somehow not in congruence with the current "super ideals"?
Thanks for any insights.
Joe H

 

[belle]

what numbers were you working with?

 

[strmrdr]

without the right star and lower half info you wont get the right reading.

 

[Rman222]

Belle,
I tried it with several but here is one:
http://www.whiteflash.com/hearts_arrows/A-Cut-Above-H-A-cut-diamond-1732614.htm

This is an ACA 1.016

When I put in the depth, table, crown angle, pavilion angle, culet, girdle, polish and symmetry, and then try all the combinations I can for star% and lower half% I can never get an "excellent". It almost always comes out "very good" with an occasional "good" with some very off star and lower half %s.

I tried it with a number of others and got the same results and was just kind of surprised and was wondering what it meant.

Thanks,

Joe

 

[Rman222]

Belle,
Here is anohter one:

http://www.whiteflash.com/hearts_arrows/A-Cut-Above-H-A-cut-diamond-703951.htm

I tried all the combinations available for star and lower half% and couldn''t get above "very good".

As I said before, I am curious if I am doing something wrong or just what it means.
Thanks,
Joe

 

[strmrdr]

60.8
55
34.5
40.8
50
80
thn
thn
non
ex
ex

gets an exellent.

use 41 and its very good, the actual is 40.9

round the depth up to 61 and use 41 and its also exellent.

rounding sux......

 

[strmrdr]

fyi 50 and 80 for stars and lgf will be correct for most ACA''s

one side effect of the gia rounding is some kicken diamonds with thin girdles are going to take a hit because when the angles are rounded up it comes out with too thin a girdle and drops a grade or 2.

 

[strmrdr]

same thing with the second example you posted the rounding on the crown up to 35 puts the girdle too thin dropping it a grade.
rounding the depth up solves that.

 

[JohnQuixote]

Date: 11/15/2005 11:46:28 PM
Author: strmrdr
60.8
55
34.5
40.8
50
80
thn
thn
non
ex
ex

gets an exellent.

use 41 and its very good, the actual is 40.9

round the depth up to 61 and use 41 and its also exellent.

rounding sux......

Those two words say a lot.

Good use of depth adjustments for rounding, Strm. Yet another approach to compensate: The Sarin on the first diamond reports 40.8 PA (40.7-40.9 min and max). Using 40.8, not rounded, along with the given depth also results in Ex.

On the second diamond the min-max on the CA range from 34.4-34.8. If you use given depth along with a 34.5 CA it results in Ex as well. In this situation I believe Strms approach, above, is more valid.

It''s possible that the 34.5-35.0 leap in the crown angle option is going to make for some headaches.

 

[Garry H (Cut Nut)]

Your results are being bumped down because the calculator is getting a girdle that is about 3% and this is too thin for excellent.
BRing the total depth to say 62% and you should not have a problem.

 

[Rman222]

Thanks for the replies. I can see how the rounding or moving the numbers up or down a tiny bit makes a big difference. In those two cases it seems if you follow GIA''s instructions exactly that they would come out Very Good instead of excellent. Does that mean that GIA would grade those as Very Good or will they make adjustments or will there just be some very nice stones graded as Very Good instead of Excellent? How much difference do you think it will make in the marketplace to have a Very Good instead of an Excellent grade?
Thanks for the insights. As a consumer I find it fascinating that after reading about how long GIA has been working on a cut grade that they have used such big rounding and that such small differences are right on the line between grades.
Joe

 

[Rman222]

Gary,
When you say that the results are downgraded because a girdle of 3% is too thin to be considered "excellent" by GIA is that because it changes the angles and thus the relative calculations, or because GIA thinks a girdle of 3% is too thin in and of itself to be considered excellent? I thought a 3% girdle would be classified as "thick" and that a thin to medium girdle was more desirable?
Thanks again for the insights.
Joe

 

[strmrdr]

Its my understanding that as far as basic proportions go thats pretty much going to be it.
A stone can get knocked down farther by girdle treatments and a few other things.

edit: talking about diamonds in general from here, not ACA's AGS is Brian's lab of choice for the ACA's and that isnt likely to change anytime soon.

The truth is that such stones if they have good optical symmetry will never likely see the inside of the GIA lab.
They will get sent to AGS with very very few exceptions.

You can bet that some very smart people are planning on how to take advantage of the gia system and cut for the max weight advantage and get the EX score at the same time.
They left them plenty of room to play.

At the same time some truely awesome diamonds are going to get knocked down by the rounding.
So were either going to see some thicker girdles being cut or no thin girdle ideals sent to GIA.
Short term its the second, long term a little of both.

 

[strmrdr]

Date: 11/16/2005 8:35:05 AM
Author: Rman222
Gary,

When you say that the results are downgraded because a girdle of 3% is too thin to be considered ''excellent'' by GIA is that because it changes the angles and thus the relative calculations, or because GIA thinks a girdle of 3% is too thin in and of itself to be considered excellent? I thought a 3% girdle would be classified as ''thick'' and that a thin to medium girdle was more desirable?

Thanks again for the insights.

Joe

3% is at the thick part of the girdle not the average of the thin part which is what they have been using and I think are still going to use for the ratings on the cert.

 

[Garry H (Cut Nut)]

typo
I meant 2%