I have such a tough time with my polariscope. It seems that I need a really large gemstone in order to find the optical interference figure. With smaller stones I don't even try to use it anymore. When I say large stones I am talking about my 22 carat aquamarine. Any advice on finding optical interference figures on smaller gemstones?
Joined: Wed Jan 23, 2013 5:29 pm Posts: 1047 Location: Paris
Why is it so important for you to find the optical interference figures ? If you try to determine the optical character, it might be easier to use the refractometer.
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
Isi has a valid point. You can get the same information with a refractometer.
But, continue practicing with the polariscope. If you can locate interference colors you are looking in the right direction. If you can't, move on to the refractometer.
That being said, a polariscope is the only instrument which will detect internal strain in cubic minerals (diamonds, garnets).
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
Huh, I've never worked with a monochromatic light with a polariscope. Are you sure you're not thinking of a refractometer....or, am I just in the dark about this technique?
Joined: Sun Mar 11, 2007 10:03 pm Posts: 341 Location: San Diego
Isi wrote:
The lens "on top of the polariscope" seems to apply more to the refractometer as well...
You can use the magnifying lens from the refractometer (if it has one) on the top lens of the polariscope to see a larger image of the reaction when turning the stone or when looking for the optic figure. I am assuming that this is what 75TURBO was referring to...
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Joined: Mon May 14, 2007 11:00 am Posts: 1133 Location: Monterey, CA
terrielea wrote:
Any advice on finding optical interference figures on smaller gemstones?
The answer to that problem was the Moore's (sp?) Sphere. But, there is probably no one at the GIA who still remembers they sold them some 50 years ago.
The easiest way to do this is put your stone in an examination dish and cover it with a liquid which has an RI close to that of the stone (water is better than nothing). Place the dish in your polariscope and then, with your stone tongs, move it up and down or around until you get the interference colors. Then, use a "strainless" sphere to resolve the figure.
You can buy a small examination dish from mineralab for a couple of dollars.
Monochromatic light gives monochrome colors, while using white light produces all colors.
A lens gives one a better view of small stones, as noted previously.
A refractometer is useless for OTL stones or unpolished samples.
Joined: Thu Jun 03, 2010 1:49 pm Posts: 331 Location: South Africa
A bit late on the topic, I have 2 useful additions to my polariscope which help a lot.
Mine is a home made unit and the upgrades are simple.
I have a plain clear lens fitted over my lower polarizing lens, to rotate the stone I simply rotate the clear lens, saves having to push the stone around.
I fitted a gem clip to the lower platform, same type as on a microscope, the stone can be held in the clip and rotated for ease of use.
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