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Sorry to sound ignorant but what is the effect of longer star facets? Thanks.
 
Thanks QM. Any chance you could give it to me in two or three sentences? I will read the articles later, though.
 
Stephan -

IRL can you actually appreciate a difference in performance?



I ask because I couldn't, I'm very sure! In pictures - IS images, still photos, the vivid open blacks appeal to me - for which LGF is more important anyway. I'd prefer a stone with 50 stars with to a 60% without, but the actual length of the star facets isn't something I have a preference for one way or another.
 
I used WFs pics, I hope that''s okay -

I much prefer these images:

51/78

78-51-SMALL990998997-2.jpg
 
To these:

59/74




You can tell that even if symmetry was perfect and the picture was taken without any tilt they would still be less pronounced.

74-59-SMALL990998997-1.jpg
 
Of course, when speaking of the black hot spots like Jonathan calls them, the lower girdle length is more important.
Short lower girdles will give bigger flashes but in smaller amount than long lower girdles.
Longer stars will increase the upper girdle angle, and, it''s my impression, increase both fire and scintillation of a diamond.
Of course, as we can read in Jonathan''s tutorial, above a certain angle, the diamond will begin to leak.
You have 2 very interesting examples from Whiteflash, could you also post crown/pavilion angles in order to estimate lower and upper girdle angles? (I say estimate because there is always a very little painting/digging that will make the calculation incorrect. Only way to know is to have a Helium scan like on Jonathan''s diamond).
 
Date: 12/27/2009 3:41:48 PM
Author: yssie
51/78
http://www.whiteflash.com/round_ideal_cut/Round-Ideal-Cut-cut-diamond-2176261.htm#
34.7/40.8/61.1/56.5


59/74
http://www.whiteflash.com/premium_select_round/Premium-Select-Round-cut-diamond-2097586.htm
34.8/40.7/62.8/53.8
Click to expand...
I love number 2, it has an antique look.
30.gif

It would be nice if the optical symmetry was perfect.
Without any painting/digging (that''s of course not the case),the average upper girdle would be of 42.74 degrees (Sarin: crown 35 degrees, table 54%, star 59%).
 
I find it sad that it is so difficult to find H&A with longer star facets/higher upper girdles angles.
As discussed here, it seems like such star facets/upper girdles angles could help fire.
You can see the 1.74 O-IF I mention above and the 2.03 J-SI2 in one of Jonathan''s movie where he compares different colors in diamond. 2 fireballs...
 
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