It is with great sadness I'd like to announce Dr. Hanneman passed away on December 12, 2020. His legacy will live on forever!
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PostPosted: Wed Jun 27, 2007 6:49 pm 
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Wow Doos,

Just surfing the forum, and resting.
Can never resist your links - hit the one above, and nearly passed out - awesome work on the gemology project.

Soon I foreseen this as being the only source we need for referal.
Thanks for all the work you do :smt038

The more the project grows, the more fun it is to learn. Great job.

Love gemmsong

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PostPosted: Tue Jul 17, 2007 10:50 pm 
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Bill Hanneman wrote:
I once wrote, "If a thing is not worth doing at all, it is not worth doing well."


...wish I had said that....

...sage!

Ux4

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PostPosted: Wed Jul 18, 2007 1:52 am 
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Where HAVE you been??? Nice to see you back Ux4...


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PostPosted: Wed Jul 18, 2007 5:48 am 
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africanuck wrote:
Where HAVE you been??? Nice to see you back Ux4...


...at my age, with a college bound, meathead/scholar teenage boy, need I explain! He STILL doesn't want me to buy a house near his college so he can live with me.

...that. PLUS, rather than take pot shots at the "Harmonization Ho's" -or more accurately HO-MONGERS - I WAS busy building an arsenal for a frontal attack. However, the damage and disgrace that I feared is done, and makes a full assault useless at this point. So, I'll just poach a little from time to time.

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PostPosted: Wed Jul 18, 2007 10:41 am 
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Good to see you again, Ux4!! Like your new avatar, too :D .

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PostPosted: Tue Jan 15, 2008 2:54 pm 
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Hi,

I had some sitting down todo today and I read Godehard Lenzen's book on gemmology again ( Edelsteinbestimmung mit gemmologischen Geräten ).
It had a wonderful chapter on measuring dispersion with the TIR refractometer (actually the whole book is a gem).

As Dr. Hanneman said, it can be done but it's not easy. Well it is, but you need to do some prelimenary work.
The problem lies in the fact that the prism/hemicilinder and the lens of the refractometer also have dispersion, which makes the technique impossible todo without knowing the error produced by your refractometer. And every refractometer is different in that regard.

Shopping cart:
-narrow bandwidth interference filter (Fraunhofer C-line)
-narrow bandwidth interference filter (Fraunhofer F-line)
- 4 calibration plates of known RI of both the C and F line and of varying RI (between 1.4 and 1.8 ) .. accurately measured to the 4th decimal.
(items one and two can be substituted with a monochromater .. or whatever it is named)

Once broke, do the following:
For every calibration plate take a refractometer reading using both the red filter as the blue filter. Then record the difference between your data and the RI data provided by your supplier for those two wavelengths.
Then plot the difference on a graph, the RI on the horizontal axis, the differences on the vertical axis. Connect the 4 dots of the blue RI differences so it forms a curve and do the same for the red filter readings.
You can reuse that graph aslong as you don't change refractometers.

Once this is done the hard work is over and you can use the red and blue filters to measure dispersion. You simply take a reading using the blue filter .. check the graph for the correction error and add/deduct that error from your observation.
Do the same with the red filter.

This will give you the C-F dispersion instead of the B-G one. Although our books mention only the B-G dispersion that value is rather pointless if we can't measure it anyway (see the problems in the Australian gemmologist paper ). There are plenty sources that mention the C-F interval.
Use the ordinary ray reading for uniaxial stones and the beta one for biaxial ones.

Maybe I'll make some images to illustrate and post them (here and on the GP).

Have fun ;)

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PostPosted: Thu Jan 24, 2008 1:43 am 
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Hi Doos,
I just saw you mentioned the Lenzen book. Would you recommend to buy this book? provided it is still available?
How does it compare with Dr. Eppler, Praktische Gemmologie?

Tks

Ursula


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PostPosted: Thu Jan 24, 2008 5:37 am 
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Hi Ursula,

I have not read Eppler's book so I can't compare. Lenzen's book is quite advanced as he explores topics very indepth as you can see from the dispersion technique.
I would recommend that book when you are interested in that sort of thing. Amazon.de probably has the book.

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