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Date: 11/24/2009 6:38:19 PM
Author: Michael_E

Just for some clarity on my position. I have no horse in this race other than that I find it interesting and that it helps in the cutting of colored stones by understanding what's happening with diamonds since the same things are occurring in all faceted gems.
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That's cool. Bruce Harding is also a colored stone faceter, and was the first to identify the effects of head shadow.
 
Date: 11/21/2009 3:42:51 AM
Author: Garry H (Cut Nut)
There are none so blind as those who will not see.







Later edit after appropriate resaearch
The most deluded people are those who choose to ignore what they already know. The proverb has been traced back in English to 1546 (John Heywood)... In 1738, it was used by Jonathan Swift in his ''Polite Conversation,'' and is first attested in the United States in the 1713 ''Works of Thomas Chalkley'' http://www.funtrivia.com/askft/Question41522.html
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My personal favourite:

"When arguing with a fool make sure they are not doing the same"
Anonymous
 
Date: 11/24/2009 6:38:19 PM
Author: Michael_E
Date: 11/24/2009 3:00:43 PM


Contrast( and specially dynamical contrast) is very important for cut performance, but obscuration is worst method (for cut performance) to create contrast.
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But you aren't 'creating contrast', you are just using whatever contrast exists in the environment by choosing which parts of the environment in front of the diamond will be reflected to an observers eyes. Since the most dramatic and constant part of the environment, (since you always know where they are looking from), is the observer of the diamond, they are the only thing that you can count on to provide really strong contrast in a consistent manner. What else would you use ? Trees, cars, buildings and so forth change constantly. The horizon changes in elevation as well, so how do you get consistent contrast without using the reflection of the observer ? This question is not an objection, but a question of how you see this.


Just for some clarity on my position. I have no horse in this race other than that I find it interesting and that it helps in the cutting of colored stones by understanding what's happening with diamonds since the same things are occurring in all faceted gems.
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Contrast of diamond image is result interaction cut and light conditions. you can consider it as "Image contrast" = "Cut contrast"x"Light environment contrast"
if "Light environment contrast"= 0( for example white sphere ) "Image contrast" =0 for ANY cut
if "Cut contrast"=0( for example 90 degree prism),"Image contrast" =0 for ANY Light environment

best cut has special distribution of VF-cones , when closed( on cut space) VF's catch light from different places in light environment
In bad cut most VF's could catch light from same direction only ( most know example is strong head obscuration diamonds aka NailHead)
 
re:In bad cut most VF''s could catch light from same direction only ( most know example is strong head obscuration diamonds aka NailHead)
VCones for such VF''s in NaiHead diamond have very low( near zero) angular speed.

in good cuts VC''s have high angular speed and big angle between VC''s for closed VF''s what is create nice Dynamical contrast aka Scintillation
 
Date: 11/25/2009 1:33:28 AM
Author: Serg
re:In bad cut most VF''s could catch light from same direction only ( most know example is strong head obscuration diamonds aka NailHead)

VCones for such VF''s in NaiHead diamond have very low( near zero) angular speed.


in good cuts VC''s have high angular speed and big angle between VC''s for closed VF''s what is create nice Dynamical contrast aka Scintillation
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My benchman noticed that with the Octavia prototype while he was setting it and commented on it.
No matter which way he turned it he was getting strong light return and contrast compared to a decent cut round he was comparing it to.

I am working on a design right now that has this problem, great ASET image, looks great face up, high DC light return, but fire and scintillation is way down.
Bring them up and light return drops off.
Since it is a starting design for a client I can''t show it.
The final design will not have this issue.
 
Could I get some references to VC''s and VF''s as I''m not familiar with those terms ? Thanks guy''s !
 
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