Joined: Thu Dec 18, 2008 11:34 am Posts: 95 Location: UK
hi there all...i hope you are all well.... the exams are looming!!
And i'm just browing tourmaline....can someone just confirm to me, although i did read it in a chat, but i can't find it now.....very annoying... If we want to make the the colour look darker, we cut Tourmaline with c axis at 90 degrees to the table?? And if we want it lighter, then parallel with the table? is this correct or is it the other way round!!!
That is generally right yes.
The stone usually looks darker when you have the C-axis orientated so that you look down the C when viewing through the table.
Joined: Thu Dec 13, 2007 3:42 pm Posts: 4091 Location: the Netherlands
Only slightly related but still fun:
Did you know the very first polariscopes were composed out of two slices of tourmaline? (which was possible because one of the rays (forgot which one) can get fully absorbed thus making the slice a polarizing sheet)
even though i've never used a polariscope, that's very interesting, tim!! thanks for sharing that with us!! interesting site, too!! and if you have questions, you have to fill out a web form for further info. ?
Hi,
This is not always the case watermalons and some others having dark outer coating of other colors may be look lighter from C-axis and dark from a-b axis.
Don't mind if you feel i am wrong.
_________________ I only trust the one which is faceted by myself,whether it is badly cut or well cut.
Tourmaline is strongly doubly refractive and pleochroic (even stronger than zircon or peridot) One being much darker than the other. Cutters try to orientate the gems table so the lighter pleochroic colour is visible. However to darken pale rough you orientate the table so its perpendicular to the crystals length and vise verse. You also have to think about cleavage and stability though when deciding on cutting direction. Hope that helps.
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