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 Post subject: Polariscope use
PostPosted: Wed Apr 11, 2018 8:21 pm 
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I'm currently in the gem ID lab course and enjoying myself immensely. But I find myself struggling with the concept of proving uniaxial or biaxial while using the polariscope. With the Refractometer I can see the movement on the scale. That makes it easy, however when I move on to the polariscope even on stones I already know to be one or the other I struggle.
I'm re- reading the manual section on the equipment use to see if it's more enlightening, just seems odd that at this stage of the game I missed something basic.
Suggestions...

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 Post subject: Re: Polariscope use
PostPosted: Wed Apr 11, 2018 8:26 pm 
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What are you using as your uniaxial reference? Adr can make this confusing.


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 Post subject: Re: Polariscope use
PostPosted: Wed Apr 11, 2018 8:34 pm 
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It doesn't seem to be on any particular stone. About the only figure I can spot reliably is a bullseye. But that doesn't lend much confidence to the rest.

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 Post subject: Re: Polariscope use
PostPosted: Wed Apr 11, 2018 8:38 pm 
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I feel like a short order chef flipping eggs on the breakfast rush. Flip spin turn I can't say I've seen much to set Barbie's magic wand on to verify anything.

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 Post subject: Re: Polariscope use
PostPosted: Wed Apr 11, 2018 8:50 pm 
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Plan is to hit this section hard for a couple of hours while I've got some instructors available. Dig up a hand full of stones with easily identifiable reactions. See how that goes. I just wonder when I fell of the boat?

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 Post subject: Re: Polariscope use
PostPosted: Wed Apr 11, 2018 9:07 pm 
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The only time we do not see "blinking" with a doubly refractive stone is when we are looking down the "C" axis.
Turn your confusing samples on their side and try again.
If you suspect a stone may be singly refractive exhibiting ADR, orient it in its lightest direction when viewed though crossed polars, turn the polarizer 90º. If it appears even lighter, it is singly refractive.

I always suggest that a student assemble a collection of study stones in order to master instruments.
Large stones are best, as we can actually see them without eyestrain.
The study stones should exhibit:

1. The stone appears dark throughout a 360° rotation.
The stone is isotropic (single refractive).
Fluorite is a good choice

2. Throughout a 360° rotation the stone blinks 4 times, light and dark.
The stone is anisotropic (double refractive).
Peridot is a good choice

3. The stone will appear light all the time.
The stone is a microcrystalline or cryptocrystalline aggregate
Light colored chalcedony is a good choice....or nephrite, jadeite

4. The stone will show anomalous double refraction (ADR).
It is isotropic (single refractive).
Red pyrope or almandine garnet is a good choice.


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 Post subject: Re: Polariscope use
PostPosted: Wed Apr 11, 2018 9:08 pm 
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We were typing at the same time.


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 Post subject: Re: Polariscope use
PostPosted: Thu Apr 12, 2018 9:31 am 
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That is a slightly different approach but mostly the same. Thank you Barbara. I have all of these stone available today so will be certain to go through this with my instructor as well.

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 Post subject: Re: Polariscope use
PostPosted: Fri Apr 13, 2018 1:55 pm 
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If you are on campus in Carlsbad, you can also ask to meet with your primary instructor who I'm sure would be happy to provide additional guidance. Or you can ask for me :)

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 Post subject: Re: Polariscope use
PostPosted: Fri Apr 13, 2018 8:33 pm 
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Ithings got cleared up nicely my confusion was with SR stones the DR stones were no issue. It was me looking for uniaxial or biaxial on SR stones. + - um hey SR yea ...
So on with the coursework I have a box of lovely red gemstones to work with when I get back to the home front. The lab was excellent love working with John the resident Britt. He was there for diamond & colored stone grading when I took that last year as well. I appreciate a dry sense of humor.

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