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Question on angle "ranges"

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alamb

Rough_Rock
Joined
Dec 2, 2006
Messages
54
I was reading over my independent appraisal and noticed that although the crown angle is listed as 35, the range listed is 34.5-35.2. I thought that was a pretty big range. I was curious what effect, if any that has and if that is a normal occurance. Also, the crown height seems a bit high compared to most that I''ve seen. Does that matter? I''m just trying to get to know my diamond better. I don''t really understand the Star and lower half length either, does it have any major effect on things?

The rest of the report is

Total Depth 62%
Table 56% (55.7-56.4)
Table off center (.2%)
Crown Height 16.2% (16.0-16.3)
Crown Angle 35 (34.5-35.2)
Pavilion Depth 42.5 (42-43)
Pavilion Angle (40.5-40.7)
Star Length 54.5%
Lower Half Length 78.7%
Culet .4
Girdle (.9-1.6)

Thank-you!
 

niceice

Brilliant_Rock
Joined
Jan 29, 2003
Messages
1,792
The variance in the high and low measurements of the range of the facets which comprise the average crown angle measurement is not alarming, although the tighter the range the better the light return is likely to be. That said, the fact that the variance in the pavilion angle measurements is so tight is excellent, especially given the fact that the pavilion angle is responsible for the majority of the light return! I''d much rather have a little fluctuation in the crown angle than in the pavilion... Nothing to worry about
 

alamb

Rough_Rock
Joined
Dec 2, 2006
Messages
54
I guess I''m still a little bit confused. Do you think the crown angle range being large has no bearing on the diamond performance? Or do you think there is some effect, but it is minimal? I guess I was thinking an ideal cut diamond would have tighter ranges because if they just take the average but the range is wide, is it really ideal?
 

JulieN

Super_Ideal_Rock
Premium
Joined
Jul 25, 2005
Messages
13,324
Date: 1/13/2007 1:55:14 PM
Author: alamb
I guess I'm still a little bit confused. Do you think the crown angle range being large has no bearing on the diamond performance? Or do you think there is some effect, but it is minimal? I guess I was thinking an ideal cut diamond would have tighter ranges because if they just take the average but the range is wide, is it really ideal?
The range on this stone is not really that large. You need an Ideal Scope to see if it has an effect. Crown variances do not affect the stone as much as pavilion variance.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
15,141
Date: 1/13/2007 4:04:02 PM
Author: JulieN

Date: 1/13/2007 1:55:14 PM
Author: alamb
I guess I''m still a little bit confused. Do you think the crown angle range being large has no bearing on the diamond performance? Or do you think there is some effect, but it is minimal? I guess I was thinking an ideal cut diamond would have tighter ranges because if they just take the average but the range is wide, is it really ideal?
The range on this stone is not really that large. You need an Ideal Scope to see if it has an effect. Crown variances do not affect the stone as much as pavilion variance.
Absolutely right.

Often large variations are a result of a tilt in the table and no visual effects are discernable at all

as in the example with this H&A''s stone with a huge variation in crown and pavilion angles
http://www.gemology.ru/cut/english/symmetry/6.htm

So you need an ideal-scope image to be sure
 
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