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Why would this stone be rated only VG cut by GIA?

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hankae

Rough_Rock
Joined
Jan 10, 2007
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13
I''m looking at the following stone and cant for the life of me figure out why it is rated only VG cut?

Round Brilliant
1.50ct
H
VS1
Cut: VG
Polish: EX
Symmetry:EX
Flou: None
Table: 58%
Depth: 62.6%
Crown angel: 35
Pavillion Angle: 40.8

It rates as a 1.9 on the HCA scale as VG, EX, EX, VG

How is it possible that it only rates as a Very Good Cut on the GIA report?
 

JohnQuixote

Ideal_Rock
Joined
Sep 9, 2004
Messages
5,212
With that depth I suspect the girdle is thicker than GIA will allow for EX. Do you know the girdle range or mm measurements of the whole diamond? (edited - I was posting at the same time Daniel was)

Or, though less likely, appx. 2% of GIA round grades are influenced by brillianteering. This would be noted on the lab report.

If you have the GIA # we can go to their report service and get all the numbers.
 

belle

Super_Ideal_Rock
Joined
Nov 19, 2004
Messages
10,285
that depth is probably going to take it out of range. also, in order for a stone to get 'excellent' the girdle needs to be between 'thin and slightly thick'. if it is out of that range...the 'grade' goes down.
 

colorkitty

Shiny_Rock
Joined
Nov 28, 2006
Messages
220
What belle said. Your stone is .3% too deep to be considered ideal (I believe). However, if you''ve seen it, loved it, and it scores good on the HCA, I don''t see a reason to rule it out.
 

DBM

Shiny_Rock
Joined
Oct 24, 2006
Messages
404
ahh you know belle might be right... i have a vague recollection of 62.3 being the range for GIA for Ex depth ... but don''t remember for sure.
 

hankae

Rough_Rock
Joined
Jan 10, 2007
Messages
13
The girdle on the first diamond, the one that it 1.50 ct is medium to thick.

Also,

I was looking at this one that is rated as EXCELLENT cut by GIA, but the HCA numbers are terrible. Which is the better stone?

Round Brilliant
1.38ct
G
VS1
Cut : EX
Polish: VG
Symmetry: VG
Flou: None
Table: 55
Depth: 62.6
Crown angle: 36.0
Pavillion angle: 41

Thin to medium Girdle

It rates a 5.1 on the HCA scale as G,G,G,VG
 

hankae

Rough_Rock
Joined
Jan 10, 2007
Messages
13
Date: 1/12/2007 10:41:15 AM
Author: DBM
ahh you know belle might be right... i have a vague recollection of 62.3 being the range for GIA for Ex depth ... but don't remember for sure.
The second one I'm looking at has a 62.6% depth and is rated GIA EXCELLENT.
 

hankae

Rough_Rock
Joined
Jan 10, 2007
Messages
13
Date: 1/12/2007 10:31:11 AM
Author: JohnQuixote
With that depth I suspect the girdle is thicker than GIA will allow for EX. Do you know the girdle range or mm measurements of the whole diamond? (edited - I was posting at the same time Daniel was)

Or, though less likely, appx. 2% of GIA round grades are influenced by brillianteering. This would be noted on the lab report.

If you have the GIA # we can go to their report service and get all the numbers.
The girdle is medium to thick and the total measurements of the stone are 7.24*7.27*4.54
 

belle

Super_Ideal_Rock
Joined
Nov 19, 2004
Messages
10,285
Date: 1/12/2007 10:41:41 AM
Author: hankae

I was looking at this one that is rated as EXCELLENT cut by GIA, but the HCA numbers are terrible. Which is the better stone?
the better stone is the one that looks better to you.

if you can't see them in person, i would definitely go with the first one.
i have a stone that is *only* gia 'very good' and it is awesome. other than the thinner girdle, it would have been an 'ex'.

take the gia 'cut grades' with a grain of salt. they tried and missed on that venture.
 

JohnQuixote

Ideal_Rock
Joined
Sep 9, 2004
Messages
5,212
Diamond #1 being VG while diamond #2 is EX is a combination of factors.

Most significant is that the girdle on diamond #1 ranges to thick. That disqualifies it. Still, we have 2 diamonds of 62.6% depth with different grades. Why?

This is an interesting case where if diamond #1s table was smaller (allowing more crown height) or the depth was lower (taking weight from the girdle) it would receive EX - as long as the girdle range was limited to STK. Meanwhile, though the crown and pavilion angles are steeper/deeper than preferred in some professional quarters, diamond #2 has a small enough table (allowing more crown height) and thin enough girdle to receive EX.

At my workplace we would predict diamond #1 to be the more appealing stone from a light performance standpoint, but that's according to our preferences. Once diamonds start getting > 62.0 in depth we also start looking at spread to weight ratio.

HankaeFW.jpg
 

JohnQuixote

Ideal_Rock
Joined
Sep 9, 2004
Messages
5,212
For anyone curious about the nuances of this system:

If we limited diamond #1 to STK girdle and added crown height, giving it a smaller table, it would get EX.
If we limited it to STK and kept the same table but reduced the depth appropriately it would also get EX.

HankaeFW2.jpg
 

JohnQuixote

Ideal_Rock
Joined
Sep 9, 2004
Messages
5,212
Date: 1/12/2007 10:43:55 AM
Author: hankae


Date: 1/12/2007 10:41:15 AM
Author: DBM
ahh you know belle might be right... i have a vague recollection of 62.3 being the range for GIA for Ex depth ... but don't remember for sure.
The second one I'm looking at has a 62.6% depth and is rated GIA EXCELLENT.
GIA EX allows up to 63% depth depending on configuration. They limit girdle thickness but some crown and pavilion combinations in conjunction with 3%-ish girdles climb into the high 62s.

HankaeFW3.jpg
 

DBM

Shiny_Rock
Joined
Oct 24, 2006
Messages
404
Date: 1/12/2007 11:33:11 AM
Author: JohnQuixote

Date: 1/12/2007 10:43:55 AM
Author: hankae



Date: 1/12/2007 10:41:15 AM
Author: DBM
ahh you know belle might be right... i have a vague recollection of 62.3 being the range for GIA for Ex depth ... but don''t remember for sure.
The second one I''m looking at has a 62.6% depth and is rated GIA EXCELLENT.
GIA EX allows up to 63% depth depending on configuration. They limit girdle thickness but some crown and pavilion combinations in conjunction with 3%-ish girdles climb into the high 62s.
thank you john
 

hankae

Rough_Rock
Joined
Jan 10, 2007
Messages
13
Date: 1/12/2007 11:22:40 AM
Author: JohnQuixote
Diamond #1 being VG while diamond #2 is EX is a combination of factors.

Most significant is that the girdle on diamond #1 ranges to thick. That disqualifies it. Still, we have 2 diamonds of 62.6% depth with different grades. Why?

This is an interesting case where if diamond #1s table was smaller (allowing more crown height) or the depth was lower (taking weight from the girdle) it would receive EX - as long as the girdle range was limited to STK. Meanwhile, though the crown and pavilion angles are steeper/deeper than preferred in some professional quarters, diamond #2 has a small enough table (allowing more crown height) and thin enough girdle to receive EX.

At my workplace we would predict diamond #1 to be the more appealing stone from a light performance standpoint, but that''s according to our preferences. Once diamonds start getting > 62.0 in depth we also start looking at spread to weight ratio.
John,

Wow!!!!!!what a great analysis.

Given the fact that stone #2 is local to me and I have seen it (I thought it looked great. I also looked at it with the Hearts and Arrows device and it appeared to have nice hearts and arrows), and Stone #1 is an "online" stone which I have not seen, and given the fact that stone #1 is priced at $11,100 and stone #2 is priced at $10,600, I''m leaning towards #2. I know that you prefer stone #1, however, what is your opinion on the merits of #2 and the pricing?

Thanks so much for your help.
 

JohnQuixote

Ideal_Rock
Joined
Sep 9, 2004
Messages
5,212
Date: 1/12/2007 2:10:57 PM
Author: hankae
John,

Wow!!!!!!what a great analysis.

Given the fact that stone #2 is local to me and I have seen it (I thought it looked great. I also looked at it with the Hearts and Arrows device and it appeared to have nice hearts and arrows), and Stone #1 is an ''online'' stone which I have not seen, and given the fact that stone #1 is priced at $11,100 and stone #2 is priced at $10,600, I''m leaning towards #2. I know that you prefer stone #1, however, what is your opinion on the merits of #2 and the pricing?

Thanks so much for your help.
You''re welcome hankae. Glad to help.

On paper both of those diamonds run too deep for my preference. The crown and pavilion angle combination indicates some loss of light return. Additionally, a near-Tolkowsky 1.38 ct round will have appx 7.22 mm of spread at 61% depth. A 62.6% will face up smaller (though it may not be a visible difference and of no concern). Of course, I''m playing the numbers game, whereas you''ve seen the actual diamond and are in a better position to judge. If you''ve seen it through a range of lighting conditions, away from the jewelry store spotlights, and it speaks to you that''s what''s important.
 

hankae

Rough_Rock
Joined
Jan 10, 2007
Messages
13
Date: 1/13/2007 4:12:23 PM
Author: JohnQuixote

Date: 1/12/2007 2:10:57 PM
Author: hankae
John,

Wow!!!!!!what a great analysis.

Given the fact that stone #2 is local to me and I have seen it (I thought it looked great. I also looked at it with the Hearts and Arrows device and it appeared to have nice hearts and arrows), and Stone #1 is an ''online'' stone which I have not seen, and given the fact that stone #1 is priced at $11,100 and stone #2 is priced at $10,600, I''m leaning towards #2. I know that you prefer stone #1, however, what is your opinion on the merits of #2 and the pricing?

Thanks so much for your help.
You''re welcome hankae. Glad to help.

On paper both of those diamonds run too deep for my preference. The crown and pavilion angle combination indicates some loss of light return. Additionally, a near-Tolkowsky 1.38 ct round will have appx 7.22 mm of spread at 61% depth. A 62.6% will face up smaller (though it may not be a visible difference and of no concern). Of course, I''m playing the numbers game, whereas you''ve seen the actual diamond and are in a better position to judge. If you''ve seen it through a range of lighting conditions, away from the jewelry store spotlights, and it speaks to you that''s what''s important.
I really like this stone, I saw it again yesterday. I can get it for $10,500. I just want to be sure I''m not paying too much. Any thoughts on the pricing?

Thanks
Hank
 

Midway

Rough_Rock
Joined
Nov 29, 2006
Messages
65
Hank, if you have seen the stone and you love it then the price you are paying is not a bad one. I considered many stones with similar carat, cut, color and clarity parameters that you seem to be looking for, and $10,500 for that kind of stone is not a bad price.

But what I would say is pay more attention to the diameter size when you are trying to determine whether a particular stone is a good price. What are the dimensions of stone #2? The problem with deeper stones is that you often lose out on diameter, and that''s the size that you or she is really going to see.

If the 1.38 that you are looking at is in the 7.1X range, then I would reconsider my options. For $10,000+ dollars you should be able to get an triple ideal/excellent, G, VS stone with a ~7.2X diameter range. I know it''s only a tenth of a mm but for me it''s actually quite noticeable. Also, it''s score on the HCA is cause for some concern. Like others have said, it may look great under the jeweler''s lights but lots of stone can look great in that lighting. The real test will be how it looks in all different lighting conditions, and whether you are really getting an optimally performing stone. Don''t get too caught up in the numbers but make sure that you''re getting a stone that actually looks like a 1.38 carat. I''d be a shame to pay the price for the carat weight but end up with something that *really* looks like a 1.25 carat stone.
 
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