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Twist between upper and lower facets

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Turtle

Rough_Rock
Joined
Apr 10, 2003
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16
On some diamond reports, a property of "twist" is measured.

I have included a pic that Garry Holloway provided in this thread:

https://www.pricescope.com/community/threads/template-of-diamond-info.4933/

This seems to be an area that has not been discussed much. What is an acceptable amount of twist between the top and bottom facets? From the pick Garry posted, this particular diamond has a minimum twist of .3° and a maximum twist of 2.3° with an average of 1.1°. Is this an acceptable range? Many vendors quote that the variance between crown and pavillion angles is less than 1° which shows precise cutting. What range of twist in degrees shows precise cutting? Should a dimaond be avoided because of excessive twist? How much is too much twist? Visually, what affect does excessive twist have on the diamond? Poor B-scope images? Poor Firescope images?

Thanks for your help!


sarin_twist.jpg
 

Turtle

Rough_Rock
Joined
Apr 10, 2003
Messages
16
Bump. Ok, let me ask another way. If 7 of the 8 facets have around 1° to 2°s of twist and then one of them has 9° of twist, should that be a concern?
 

pyramid

Ideal_Rock
Premium
Joined
Nov 10, 2002
Messages
4,607
I am quite interested in this. I had never heard of it before.
Can CutNut or one of the other experts comment? It sounds as if it may be quite complicated like those drawings Serg deals with!
 

Serg

Ideal_Rock
Trade
Joined
Mar 21, 2002
Messages
2,519
Small twist does not mean good optical symmetry ( The twist between opposite facets is very important)
Big twist does not mean bad optical symmetry
Sarin-OGI twist mistake is more than 0.5( may b 1-2) degree
 
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