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PostPosted: Fri Mar 10, 2006 11:59 am 
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Snizzy;

Our instructor for the CGA course spent time demonstrating the pavillion flash and from what I remember, the course notes had a page or two on it. I'll have to see if I can dig them out.


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PostPosted: Fri Mar 10, 2006 7:21 pm 
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Hey, Sniz! Thanks for showing your notes! I wondered why I could never find a shadow pattern --I didn't know the stone had to be immersed :oops: :lol: !


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PostPosted: Fri Mar 10, 2006 8:22 pm 
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MoDo - these are the same notes that you have - it's in the GEM ID course, Lesson 12.


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PostPosted: Sat Mar 11, 2006 7:47 pm 
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Whoops! Color me blonde :lol: (no offense, Sniz :oops: ). I told you my memory is no good!


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PostPosted: Wed Mar 15, 2006 5:39 pm 
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Well, I've visited just about every link that has the keywords "pavillion flash" or something similar in it.

So far no explaination as to the cause except, the unexplained dispersion.
I think we all know what dispersion is but, that's not really a mechanical explaination of how it works in regards to the limited range of colors you see associated with pavillion flash in some highly dispersive simulants.

I have a theory that involves critical angle and only a portion of the spectrum falling within this angle as it exits the pavillion,(one of the reasons not to tilt the stone and change the angle much) but don't know if enough dispersion could take place to allow only a portion of the spectrum to exit independantly of the other color componets. I just cant seem to find a consistent relationship between the different dispersive values and the resultant colors of the flash.

Next step, before I really start sounding stupid, is maybe a phone call or two to someone who is sure about this anomoly. Surprising how many people aren't familiar with this observation and how little it's mentioned outside of the classroom.

One reason I don't think it would be affective for colored simulants is, selective absorbtion could produce any number of different effects unless I'm way off track and hunting in an empty field.(Which would be good if Dick Cheney is around). :)


Last edited by JB on Thu Mar 16, 2006 2:27 pm, edited 2 times in total.

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PostPosted: Wed Mar 15, 2006 5:48 pm 
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This is getting interesting! How then, can we explain the tsavorite and tanzanite colored CZ's that I've seen that both had an orange pavilion flash? 8)

Duck JB, Dick's got a gun!!!!


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PostPosted: Wed Mar 15, 2006 5:55 pm 
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Don't know Sniz. That's what I'm trying to figure out. All of these observation tests they teach us only refered/applied to colorless RB diamonds and simulants. I think they noted that somewhere. I have to go back and check.

Could be coincidence or some other mechanics at work. Would really need a wide variety of colored stone simulants of each type that exhibits this flash to do any accurate testing.


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PostPosted: Wed Mar 15, 2006 5:59 pm 
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A new project! Barbra is working on getting some colored YAGs for us!

I love this stuff....


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PostPosted: Wed Mar 15, 2006 6:02 pm 
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I'm confident that we will get the expected results with the specific RB colorless stones....my question is WHY, WHY, WHY. (wasn't yelling, just emphasizing) :)


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PostPosted: Wed Mar 15, 2006 6:05 pm 
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What does Doos mean by "TIR"?

I've seen the pavilion flash on colorless stones - now I'm fascinated with seeing it on colored stones!!!!

Why ask why? :lol: Just kidding - of course we want to know WHY! WHY! WHY!


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PostPosted: Wed Mar 15, 2006 6:17 pm 
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Total Internal Reflection. Diamond cutters attempt to fashion the stones with precise angles so light entering the crown bounces off the pavilion facets outside of the critical angle so it reflects several times before finally exiting the crown facets. Thus losing no light from unplanned light leakage in the pavilion. This can only happen at precise mathematical angles.


Last edited by JB on Thu Mar 16, 2006 2:24 pm, edited 2 times in total.

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PostPosted: Wed Mar 15, 2006 6:20 pm 
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I was aware of the definition - just don't remember hearing it refered to as "TIR". Did I miss another part of my lab manual, JB? :oops: Or does GIA have another fancy set of initials to describe it? :D


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PostPosted: Wed Mar 15, 2006 6:22 pm 
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Gemology is like the military. We only speak in acronyms. :lol:


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PostPosted: Sun Mar 19, 2006 1:43 pm 
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RE: Pavilion flash.

I contacted one of my former lab instructors regarding this and he said that it's believed to be connected to dispersion. It's also thought that cut may play a role as well because, they have seen some diamonds that have the orange or yellow pavilion flash that is normally seen in CZ.

He is going to contact headquarters (GIA) and see if he can get the technical information on this. I'll keep you updated once he gets back with me. :)

For now, proceed knowing that this is just a general observation and may not be written in stone. There may be factors that could influence an unexpected reaction.


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PostPosted: Sun Mar 19, 2006 2:12 pm 
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That's excellent info, JB. Do keep us informed.
I took out a number of diamonds we had in stock yesterday and tested to see if I observed a pavillion flash. Ocassionally the first flash observed was a distinct, broad and very pronounced orange! Upon slightly rotating the diamond, I eventually got the desired blue/violet. But, if those diamonds were mounted, it could have been impossible to angle them to see the correct color.


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