New Mineral Named After GIA’s John Koivula
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 Post subject: Gemology Geek
PostPosted: Thu Mar 09, 2006 12:16 pm 
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I'm probably the only person who is fascinated by this stuff - but in the GIA GEM ID course - there is a section about diamond simulants in which they list certain characteristics for each simulant.

One of them is "pavilion flash" and I guess I never gave it much thought, as I assumed it only pertained to colorless stones. Recently I have encountered some loose CZ's that clients brought in for gem identification - one in a tanzanite color and the other a tsavorite color. I noticed immediately that both of them had an orange pavilion flash and after testing both of them to confirm CZ - I thought it was interesting that even the colored stones would show an orange pavilion flash.


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PostPosted: Thu Mar 09, 2006 1:55 pm 
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I don't understand what that means.
Are you aware of any photos that illustrate this "flash"?


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PostPosted: Thu Mar 09, 2006 2:06 pm 
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You mean they didn't teach pavilion flash at GIA in the 80's? :shock:

When you look at some colorless stones, pavilion side up, under reflected light - if you gently rock them back and forth - you will see a pavilion flash on some of them.

CZ shows an orange flash, YAG shows a blue and violet flash, Strontium Titanate shows a multi colored flash, GGG shows an orange and blue flash, and Diamond shows an orange and blue flash. Zircon and Synthetic Rutile show no flash of color.

Photo to follow....


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PostPosted: Thu Mar 09, 2006 2:14 pm 
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Here's the photo.

CZ on the left has a mostly orange pavilion flash, YAG in the middle shows blue and violet, and Diamond on the right shows almost equal amounts of blue and orange.

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PostPosted: Thu Mar 09, 2006 3:57 pm 
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Nice,

Never heard of that one either.

I also enjoy doing the tilting test where you look at the table and then tilt it back 45 degrees. In well cut brilliants the table stays light (due to TIR) for simulants with a smaller RI, the table will turn dark.

And of course the dot test. Draw a small dot on a sheet of white paper, lay the stone table down on it .. in diamond you should not be able to see the dot when it has good proportions. In simulants with smaller RI the dot will form a ring around the culet.


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PostPosted: Thu Mar 09, 2006 5:35 pm 
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RE: Pavillion flash.

My lab instructor taught us to observe the flash under 10X in darkfield lighting and to not tilt the stone, although you may have to tilit slightly just a few degrees for the flash to appear. If you tilt to much the colors will change.

I don't know how affective this would be for Colored OTL stones or stones other than RB. The question never came up.

I can take a picture of the diamond simulant separation sheet they gave us and post it here if you like.


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PostPosted: Thu Mar 09, 2006 8:41 pm 
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Hell's Bells!!
It works.
I took a cz and viewed it JB style and orange flash there was.
Unfortunately, I don't own a yag but I trust that a blue flash would be there.

Thanks for that tip!

PS....No, they didn't teach about pavillion flash in the 80's. What causes it?

PSPS Yes JB, I'd like to see that seperation sheet


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PostPosted: Thu Mar 09, 2006 9:14 pm 
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I didn't have an instructor show me the technique during lab - I just read about it in the course material.

There are two ways to see the pavilion flash - use overhead reflected or transmitted light and your unaided eyes, or you can use darkfield illumination and a loupe or microscope. If you gently tilt the stone slightly in different directions, you will see the dispersion coming from the pavilion. The size and color of this pavilion flash is an indication of identity. Of course, you will want to do other tests to confirm the identity of the stone.

As to what causes it - I have no idea. I imagine it's the chemical makeup of the stone and the way the light passes through the pavilion, but that's just a guess.


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PostPosted: Thu Mar 09, 2006 9:29 pm 
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Sniz, there are sometimes a bit of differences between the text instructions and lab instruction. For some reason the lab method stuck with me. Whichever way works best for anyone would be effective.

I hope this enlarges enough to read. I don't have a scanner. Keep in mind these are just observation techniques as Snizzy said. You must do other tests to confirm.

Image


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PostPosted: Thu Mar 09, 2006 9:51 pm 
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That's funny JB! :lol: :lol: The lab manual that you used contradicts the Lesson 12 course material that I used. You gotta love it that they would contradict themselves in the same course.... but you're right - whatever works for the individual to attain the result is fine.

This is where my info came from:

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You can probably tell that I do tons of highlighting and underlining... :wink:


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PostPosted: Thu Mar 09, 2006 9:55 pm 
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This is what I thought you were going to post, JB:

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Image
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I don't remember seeing your information in the lab manual, but I must confess that I didn't spend much time with the lab manual - I mostly used the individual lessons for my GEM ID course. (All highlighted and underlined, of course 8) )


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PostPosted: Thu Mar 09, 2006 9:59 pm 
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Doos,

This reminded me of what you were talking about with the dot test, only it is done with SG liquids.

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PostPosted: Thu Mar 09, 2006 10:02 pm 
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The document I posted was a single page handout thet gave us in lab. They also had us change some stuff in the lab manual.

Shrug. :)

There were no copyright marks on it so I figured.......


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PostPosted: Thu Mar 09, 2006 10:10 pm 
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I remember asking Barbra about copyright laws when posting written material in forums, and I think we're okay. Can't remember the exact verbiage though.

The reason I thought you would post the 2 page "separation sheet" was because it never dawned on me that you had one from the lab manual, as the only one I know of was in Lesson 12. Of course if I ever looked in my lab manual.... maybe I would find one :oops:


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PostPosted: Fri Mar 10, 2006 11:57 am 
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The only logical explanation for these flash figures will be TIR (which doesn't work very well on the pavilion).


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