Date: 3/1/2007 5:11:08 AM
Author: DiaGem
Date: 3/1/2007 3:07:26 AM
Author: Garry H (Cut Nut)
Date: 2/28/2007 1:21:56 PM
Author: strmrdr
1st: DD stuff is a red herring. The DD isnt in my opinion why the system is bad.
Storm I have had a small window of opportunity to do some testing inside Diamond Dock.
I used 2 princess cuts chosen at random and one shallow ish round that I happened to have with me.
The photo''s on the top row have the fluoro only lights on and are taken at about 40 - 45 dgerees between the stones and the light center point (the viewing angle that I believe was used in the GIA survey to set the proportion grades).
I think you would agree that had I found better examples of princess cuts (I had already bought the best ones and they were packed away) then this grading environment would favour princess cuts over rounds. i.e. princess cuts would be morre ideal than ideal cut rounds!
Why, because they (princesses) are brighter? No - these princess cuts are not even close to brighter other than when you see them in DD.
I still think the round has what the GIA calls ''Positive Pattern'' (as in figure B- 1). DD was not used to discover pattern - they used salad bowls for that.
The lower photo''s are a bit fuzzy because they were taken with the lights off and I had some camera shake because the exposure time was longer.
In fact you very clearly see the round stone is far brighter with just the ambient room light - and this is the normal situation.
Depends on the kind of lighting, angle of view, and obstructions nearby, the ''positive or negative pattern'' can be noticed even in ambient room light..., don''t you agree? Of course - but they were using DD with fluoro''s for brightness. If bad patterns were noticed then this could become part of their so called ''scintillation'' study, but they have not shown any evidence of quantification in their very long article.
I fail to see how a grading environment that gets such a fundemental difference wrong can be used as the basis of a multi billion dollar decision making process.
I agree with you on that one..., but someone has to define a grading environment..., would you base a grading environment only on ''Natural Northern daylight''? I do not have an answer - it depends on the type of jewellery and the type of buyer / owner / user. e.g. an evening piece should have different grading lighting than an engagement ring.
Is this a red herring?
Garry,
GIA wrote on page 218:
Thus, given the interdependence of flashing
light and distribution, we decided to use two terms
to represent these different aspects of scintillation.
Sparkle describes the spots of light seen in a polished
diamond when viewed face-up that flash as
the diamond, observer, or light source moves.
Pattern is the relative size, arrangement, and contrast
of bright and dark areas that result from internal
and external reflections seen in a polished diamond
when viewed face-up while that diamond is
still or moving. As such, patterns can be seen as
positive (balanced and cohesive patterns; see figure
B-1) or negative (e.g., fisheyes, dark centers, or irregular
patterns; see figure B-2).
They are nice words - but there is no metric or quantification. And that was our point in both the original article and the exchange of letters. They quoted %''s of match of computer derived metrics and observation results and used the nice words above to explain why there was only a 58% match.
It makes perfectly sense to me!!!
BTW, I would go for the round and not for the princesses in that first row of yours!