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75% lgf with 45% upper, are these acceptable?

hearts-arrows_girl

Brilliant_Rock
Joined
Apr 18, 2007
Messages
1,111
I am looking at a stone that has an LGF of 75% I read the tutorials on this, and it seems fine. I cannot find any info on the (Star?) upper facet numbers. I usually see 50%, I am looking at one that has 45% Will that lower percent be fine with a 75% lgf? Or can anyone link me to a tutorial with examples on the crown facet percentages? I don't want the scintillation or fire to suffer. Thanks!
 

dreamer_dachsie

Super_Ideal_Rock
Joined
Dec 16, 2007
Messages
24,364
Stone I read the article and it does not really answer this question. Can you respond in your opinion?
 

Stone-cold11

Super_Ideal_Rock
Joined
Sep 9, 2008
Messages
14,069
Don't think it will matter that much. But idealscope/ASET image of the actual stone will tell more.
 

diamondseeker2006

Super_Ideal_Rock
Premium
Joined
Jan 11, 2006
Messages
56,145
Stone-cold11|1304962988|2916411 said:
Don't think it will matter that much. But idealscope/ASET image of the actual stone will tell more.
I'm kind of glad to see this response because I can't ever recall us debating the best upper facet numbers! I thought surely we have enough info when we have an ideal cut stone with idealscope and possibly ASET!
 

diamondseeker2006

Super_Ideal_Rock
Premium
Joined
Jan 11, 2006
Messages
56,145
Dreamer_D|1304963550|2916417 said:
I don't think the OP can get an IS image.
I see. I just can't deal with stones without more than the lab report unless they are AGS0, and in that case, we already know the light performance! Everyone needs to start providing IS images if they want to be competitive. Of course, they may not if the stones are not well cut... :naughty:
 

hearts-arrows_girl

Brilliant_Rock
Joined
Apr 18, 2007
Messages
1,111
Stone-cold11|1304960907|2916376 said:

I read the article, very interesting how it shows the relationship between the lgf and the star %.
Is there an optimal star %?
This is a GIA stone I am considering, and I don't have any IS images.
I think since no one said, "ohhh, 45% would be horrible, run!!!", I will assume 45% shouldn't be a deal breaker.
Thank you all for getting back to me. :appl:
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,451
what are the crown and pavilion angles?
upper% makes a difference in the upper girdle angle which can effect performance in certain combos.
In general there isn't a huge difference in performance between 45/50/55 in many combos but it can make or break a marginal combo because of the upper girdle angles.
In general low% uppers go with steeper crown angles and higher% with shallower crown angles.
50% is a happy medium that works with the most combos.
 

hearts-arrows_girl

Brilliant_Rock
Joined
Apr 18, 2007
Messages
1,111
Karl, that makes sense since the crown is 35. Thanks for getting back to me. My vendor is trying to get the stone in. Everything else looks great.

Crown 35
Pav. 40.8
Table 55
Depth 61.7
LGF 75%
Star 45%

It gets an HCA of 1.5
 

Karl_K

Super_Ideal_Rock
Trade
Joined
Aug 4, 2008
Messages
10,451
45% should be fine with that combo.
 
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