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 Post subject: Thinking outside the box
PostPosted: Tue Oct 02, 2007 2:17 pm 
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Hi,

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?


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PostPosted: Tue Oct 02, 2007 2:43 pm 
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white light source + gem + white paper + ruler to measure dispersion + fancy math/physics.


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PostPosted: Tue Oct 02, 2007 2:51 pm 
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Hi,

Sounds like a Nelson fingerprinting .. I like it.
More?


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PostPosted: Tue Oct 02, 2007 3:10 pm 
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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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PostPosted: Tue Oct 02, 2007 3:27 pm 
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Hi,

You may throw your rod my way anytime.


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PostPosted: Tue Oct 02, 2007 4:12 pm 
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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?


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 Post subject: Visual Optics
PostPosted: Tue Oct 02, 2007 5:36 pm 
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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. :idea:

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PostPosted: Tue Oct 02, 2007 5:59 pm 
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Doos wrote:
Hi,

You may throw your rod my way anytime.


*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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PostPosted: Wed Oct 03, 2007 8:27 am 
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Ask Doos to look at it :lol:


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PostPosted: Wed Oct 03, 2007 10:30 am 
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Hi,

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)


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PostPosted: Wed Oct 03, 2007 2:03 pm 
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Hi Doos,

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 :)

Frank


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PostPosted: Wed Oct 03, 2007 2:51 pm 
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Hi Frank,

Everyone can play, I hope to learn from it aswell.
I can come up with 13 techniques (some of which are mentioned).


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PostPosted: Wed Oct 03, 2007 4:03 pm 
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Doos wrote:
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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PostPosted: Wed Oct 03, 2007 4:10 pm 
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Hi,

Quote:
How does this pinhole refractometer work?

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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PostPosted: Thu Oct 04, 2007 1:44 pm 
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Hi,

No more bets?
The gemmological textbooks are full of options and sometimes those techniques come in very handy.
This is not just a geek thread.


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