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 Post subject: measuring dispersion
PostPosted: Wed Nov 16, 2005 9:28 am 
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Can i measure dispersion of below the limit gems by removing the yellow filter on my refractometer and recording the spread of the difference of the red and blue spectra on the refractometers scale? (whew).. is this repeatable with all quartz, then varying with topaz differing dispersion, but having a repeatable spread with other topaz?..

On above the limit gems like diamond and moissenite for instance can i put a light to the gem on a white card and hold it say 12 inches from the white card and get the same dispersion between the blue and red spectra with all diamonds?.. then a different measurable dispersion with the same light and same distance on the white card with moissenite, then having a repeatable distance between the blue and red spectra with other moissenite?? ? i realize moissenite will have a doubling effect.. dave...


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PostPosted: Wed Nov 16, 2005 11:50 am 
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Dave,

For gems that are in the limits I would try a blue and a red filter, then measure the difference .. never tried it, but I don't see why it doesnt work.

For OTL gems you could try to duplicate a spectroscope. Using a narrow slit and a beam of red or blue light and the gem in between to act as the prism. I think you could record that on a piece of paper.

Sounds like something Hanneman would try.


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PostPosted: Thu Dec 15, 2005 11:03 pm 
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Doos wrote:
Dave,



Sounds like something Hanneman would try.



Did you mean Hanuman of Ganoksin? :lol:


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PostPosted: Fri Dec 16, 2005 11:08 am 
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No Dr. Hanneman of Hanneman Gemological Instruments.
Hanuman is Dr. Aspler.


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PostPosted: Fri Dec 16, 2005 3:23 pm 
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No Dr. Hanneman of Hanneman Gemological Instruments.
Hanuman is Dr. Aspler.


Dr. Asplers stage name is Hanuaman. Ive known him since Ganoksin was still a wee little tot. He is a great guy, and knows his stuff. Knowing how he is I thought maybe you were saying he had tried it, which I would not doubt as he will try anything and everything to do with gemstones. He is really a cool guy. Now I haven’t heard of Dr. Hanneman , but it sounds like I should check him out. Thanks for clarifying that

Daniel


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PostPosted: Tue May 15, 2007 1:08 am 
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Doos, wrote "For gems that are in the limits I would try a blue and a red filter, then measure the difference .. never tried it, but I don't see why it doesnt work.

Sounds like something Hanneman would try.
------
Been there, done that. It doesn't work.
It's a long story.

Measuring dispersion with a refractometer is a very difficult task. Nevertheless, it can be done. However, I once wrote, "If a thing is not worth doing at all, it is not worth doing well."

One can use the Hodgkinson method to estimate the birefringence:dispersion ratio which is sufficient for most identification work.


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PostPosted: Thu May 17, 2007 9:11 am 
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Are you the Hanneman of Affordable gemology?
Everyone here saw my book and they are asking where can they get one? Any available in Thailand? What happened to Washington state which is as far away from Orlando Florida as you can get.

This is a must have book. I swear. Well that's all I have to say.


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PostPosted: Thu May 17, 2007 10:56 am 
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http://www.mineralab.com/Gemology.htm

http://www.prettyrock.com/php/product-d ... uments.htm


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PostPosted: Sun May 20, 2007 9:26 am 
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thanks. will show the gang at aigs gem id class who were looking for the book the link.


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PostPosted: Sun May 20, 2007 4:50 pm 
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If you really want to measure dispersion, use a Hanneman-Hodgkinson refractometer or a Hanneman refractometer, either of which you can make yourself. Instructions and conversion tables are in the second edition of my book.


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PostPosted: Wed May 23, 2007 7:57 am 
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it sure would be nice if you could come to my house and put it together. i have the book but not mechanically inclined in the least and the refractometer doesn't get all the stones, too many are over the limit.

your chapter on spot readings really helped. it is really great to meet you. keep those letters to G&G coming. I love it when you put them in their place. Ha ha....keemoog currently in bangkok

mo do: you are missing a fun course. today we found more hackmanite. nice stuff.


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PostPosted: Wed May 23, 2007 11:23 am 
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Keemoog ... Men just love helping a woman in distress :D . Surely, there are a couple of nice guys around who would put the refractometer together for you :wink: .

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PostPosted: Fri May 25, 2007 10:10 am 
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mo do: will let you know when I get back to the states if I found someone to put it together. Keep saving those pennies for your microscope. I plan on coming back to finish AIGS courses in 2009. Is that enough planning time for you to come with me and share an apartment? I know it's only two years from now....today my jeweler friend asked me to pick emeralds for earrings. she hands me two boxes of 5 plus carats each about 50 stones so 250 carats and says find some good matches. well, that was fun. then her supplier comes by and starts opening his satchel with packs and packs of sapphires, all colors, burmese and african rubies, pearls, more emeralds etc. for about an hour and i got to play with all my portable stuff, loupe, dicroscope, mag light. oh what fun....


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PostPosted: Fri May 25, 2007 10:57 am 
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OMGosh! I barely know what I'm going to do next month, let alone in two years! :lol:

Remind me later next year, okay :P .

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PostPosted: Tue May 29, 2007 11:35 am 
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Hi,

There is a nice article by Donald Hoover and Cara Williams on the bright line technique in the newest JofG issue.
They describe the technique aswell as some extra nice observations you get get with it, such as relative dispersion and obtaining (partial) spectra with the ca. refractometer.


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