Does a thick girdle affect light performance?

[angeline]

In my other current thread on GIA Cut grade I''m looking at this stone:

Stone 1:

G SI1
Depth: 61.7
Table: 57
Crown: 34.5
Pav: 41
Polish: Very Good
Symmetry: Very Good
8.98-9.07

GIA rate the cut as ''Very Good''. The HCA gives it a 1.9 with it falling inside the GIA EXcellent box on the resulting plot and on the borderline AGS 0 box.

I ran this through the GIA Facetware Cut Estimator (GIA Facetware Cut Estimator) and if I change the girdle thickness to slightly thick the cut grade is upgraded to ''Excellent''.

Will the thick girdle affect the light performance of this stone? Will it perform as well as another stone of same proportions but with a thinner girdle?

Any opinions on this stone?

Thanks for any help,

a

 

[Finding_Neverland]

How thick is thick??

Do you have mm measurements? or a %'age listed from the Cert or Sarin??

Thicker girdles are a place for light leakage. Would you see a difference if you saw this diamond next to one with a thinner girdle?? Only your eyes could say.

This close on the scoring, sounds like you've possibly picked a winner.

 

[WorkingHardforSmallRewards]

I am no expert but I am online so i will go ahead and give the results of my findings, though look at the critically. NO, girdle thickness in itself will not affect LIGHT PERFORMANCE. However, it can do a number of other things. One key issues is that your depth percentage is right about on the money, however you didn't list your actual pavilion depth and crown height. Maybe you can calculate all of that from just the angles? but I imagine that if the girdle were particularly thick yet the depth were just on target then it seems logical to me that he must have sacrificed either crown height or pavilion pavilion depth. I understand that ideal is something like 15-15.5%, or bit higher even, for crown height and within of 42.5%-43.5% for pavilion depth. Those two figures are fairly important. However, if your light performance scores are doing well, then there is nothing to worry about in that regards.

The real issue to girdle thickness is simple. You are being charged too much for what you can see. The diamond has more weight put in on the girdle than is truly necessary. You are, of course, being charged for that weight. The real key is going to be in the length and width of the girdle, rather than its depth. Check some lower ct diamonds. If they have the same length and width but are less cts then it makes sense that you could get yourself a true IDEAL stone with higher polish and symmetry grades with maybe even a better color or clarity grade level for the same price--all because it has a thinner girdle. And yet the spread of the diamond will in fact be the exact same or within .04mm or something insignificant, just because the higher ct diamond's weight is not in the spread.

However, it is also true that the girdle thickness lowered the cut grade, which in turn will lower the price which means that you could well get a better diamond with the same light performance for less money.

I say choose a minimum color, make a decision that your diamond be "eye-clean" and no less than SI-1 (for Ering) then learn everything you need to about angles and percentages of the diamond and base your final decision on the diamond that meets those ideal angles and percentages, receives a high light performance rating and has the wides spread possible.

Then it is impossible for the girdle to affect you because you based your decision on the crucial angles and percentages and on the actual "spread of the diamond Vs. the price of the diamond" rather than on ct (only use #ct as a way to narrow search, not as a decision maker)then at that point as long as the girdle is not extremely thick so it detracts from the appearance of the diamond and it isn't very thin so it risk safety of the diamond, then you dont have to worry about girdle thickness at all.

If i am wrong about anything let me know and I will delete it, I don't know much, but it is a beginning of stuff to find out at any rate.

 

[angeline]

Date: 6/8/2007 8:49:21 PM
Author: Finding_Neverland
How thick is thick??


Do you have mm measurements? or a %''age listed from the Cert or Sarin??


Thicker girdles are a place for light leakage. Would you see a difference if you saw this diamond next to one with a thinner girdle?? Only your eyes could say.


This close on the scoring, sounds like you''ve possibly picked a winner.

Ummm... the cert is GIA and says just ''medium to thick'' - no %.

The pic is a little disturbing, the arrows are reeeellllly thin. I''ll try to post the pic.

 

[angeline]

sorry that was huge...

 

[angeline]

WorkingHard - thanks for your in-depth answer. I need some time to digest it! I appreciate it though,

a

 

[Finding_Neverland]

According to the Tutorial, the girdle should be OK. Not spot on as suggested, but OK. It's not wildly ranging. Extremely thin to Very Thick, or anything like that.

And as WorkingHard pointed out, the visual diameter may not be quite the same as a Thin or Medium. The diamond isn't an AGS0/GIA EX and the price should be adjusted accordingly.

From the Tutorial:

Diamonds with Thick, Very Thick, or Extremely Thick girdles weigh considerably more, so the spread of a diamond is reduced. But thicker girdles have little impact on a diamond's sparkle.

http://diamonds.pricescope.com/girdle.asp

As to the arrows being thin,......... I know I've heard and read about that, but it's not coming to mind right now. Hopefully someone else much more knowledgeable will chime in on that for you.

 

[fanboy]

It appears, from what I''ve seen, that Royal Asscher diamonds naturallly have thicker girdles.

 

[Lorelei]

This diamond may have thinner arrows in part due to the lower halves measurement ( lower girdle facets) A thick girdle won't make the GIA Ex cut grade.

See this thread for more info.

http://www.whiteflash.com/diamonds_info/t/articles.aspx?articleid=154&zoneid=14

 

[Garry H (Cut Nut)]

The thick girdle is probably only thick at one small spot as the stone appears to have some symmetry deviations.
It should be bright with a little less fire than some of the shorter lgf stones angeline

 

[angeline]

Finding_Neverland and Lorelei - thanks for the info and link. I shall read the tutorial (somewhere I should have looked first

)

Garry - thanks for the assessment. This stone has a 1.9 on the HCA so I think I read elsewhere that you would require tight symmetry for that score. I guess the ''Very Good'' means it''s not that tight. So I''m guessing it''s not such a winner after all. Sighh... just tryin'' to save a few bucks

a