For a place in the hall of fame I'm interested in which techniques you can come up with to determine the (approx.) index of refraction of a gemstone.
Of course we all know how to do it with a refractometer .. which other methods are there?
I know there is some kind of way to get an approximate RI with a microscope, although not how...a link someone?
*looking at Doos and trying to judge if one would dare trying to fish in his pond*
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Joined: Tue Mar 14, 2006 11:08 am Posts: 832 Location: Nashville, TN
Hmmm, what about immersion? If you know the approximate RI of the liquid you are using. The more transparent the gem immersed, the closer to the RI of the liquid. And maybe the Hodgkinson method?
There's a thread where Bill Hanneman discussed using VO, and the whole concept really appeals to me, so I think that would be the best way to guesstimate the RI without a refractometer.
*throwing it out deep feeling that it was a good thrust*
Just thought of this: If the stone is reasonably cut, and you can measure the pavilion angle, then you should be able to get a clue as to what the critical angle for the material is and from there be able to do an approximate calculation by using 1/(sine the angle)=RI, or what do you say? Not very exact by any means, but an approximate way at least.
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Jung Kee, That is basically how a Hanneman pinhole refractometer works (but then not making use of the critical angle directly). Very good thought and answer.
Crystal, Yes that is the same as the Hodgkinson method that Carrie mentioned.
Carrie, There are indeed several immersion techniques .. can you name a few?
What other methods are there? (there are a few more)
Not sure if I should be allowed to answer as I've played this game with you before. If I remember correctly we came up with seven answers lat time (or was it eight?)... Good game though
Jung Kee, That is basically how a Hanneman pinhole refractometer works (but then not making use of the critical angle directly). Very good thought and answer.
How does this pinhole refractometer work?
Doos wrote:
Hi Frank,
Everyone can play, I hope to learn from it aswell. I can come up with 13 techniques (some of which are mentioned).
That's impressive! Just to be sure: Are you meaning technicques generally available to most gemologists, or are you counting more advanced technologies using spectrometers and suchlikes as well?
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It is described in "guide to affordable gemology". Not a very complicated technique, but I'd rather let the master himself describe it.
Quote:
Are you meaning technicques generally available to most gemologists, or are you counting more advanced technologies using spectrometers and suchlikes as well?
Table spectrometers are available to gemmologists (they are not that expensive), so that one is in .
My list doesn't involve instruments over USD 2,000.00 but anything you can think of counts.
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