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Analyzing faceted stones


#1

I asked this question on a facetor’s list and got no reponse. So
I’m hoping someone can help, or send me somewhere where I can find
some info.

I recently cut piece of citrine that was handheld and faceted. I do
this quite a lot. It is asymetrical with only 5 facets on the back
and five on the front. But it works very well.

What I want to know is how would I find out why this works? I need
to have an analysis of the angles etc so that this could be
reproduced. Does anyone know anyone who does this sort of analysis
that could direct me as to how to perform it or would do it
themselves? I just need info to get me going.


#2

Well, you could measure the angle with a common protractor, but if
your angles “work”, then they are greater than the "critical angle"
for the material that you are using - in this case, quartz.
http://www.rockhounds.com/rockshop/gem_designs/refractive_index/ has
more than you probably want to know about how the critical angle is
determined from the refractive index of the material you’re cutting.
If you’re not interested in the theory behind the practice,
http://www.gemcutter.com/angles.htm has a list of the critical angles
for most gem materials. Cutting your stones at these angles will
create reproducible gems that “work”.

Have fun!
Linda in MA


#3

By “working” I’m assuming you mean you’re getting some flash.
According to John Sinkankas the pavillion angle is 43 degrees and
the crown 40-50 degrees. Get “Gem Cutting: A Lapidary’s Manual” by
Mr. S. a must have if you’re interested in lapidary. Kevin


#4

Piece of citrine that was handheld

 I recently cut (a) piece of citrine that was handheld and
faceted. I do this quite a lot. It is asymetrical with only 5
facets on the back and five on the front. 

Do you have a photograph of the stone? I and probably many others
would like to see the stone.

Best regards,
Robert Lowe