Am 23.09.2012 19:18, schrieb James Holsenback:
>
> LOL ... never mind I found a way to do it (still some tweaking left) . I
> made the pigment in the material srgbf 0.85 and put some colored
> emission media in the interior ... not exactly intuitive (to me anyways)

This is not a good idea. A gemstone does absorb light and not emit it.


I've found this page with some spectral data for gemstones:

http://www.octonus.com/oct/projects/adsorbtion_spectra.phtml

and used this data to play a bit around with your stone. And after 
getting some strange effects I noticed that you have a coincident 
surface problem within the merge.

This is exactly your gem shape but without coincident surface and it
renders even a bit faster.

#declare Gem = intersection {
   #local ndx = 0;
   #while ( ndx < 360 )
     plane {-x, 0 rotate z*-55 translate x*-2.75 rotate y*ndx }
     plane {-x, 0 rotate z*35  translate x*-2.75 rotate y*ndx }
     #local ndx = ndx + 45;
   #end
   plane {y, 0 translate y*1}
}


And I would use something like this for gems:

#macro M_Gem (Color, IOR, FadeDist)
   material {
     texture {
       pigment {rgb Color filter 1}
       finish {
         ambient 0  emission 0  diffuse 0
         reflection {0 1 fresnel on} conserve_energy
       }
     }
     interior {
       ior IOR
       fade_power 1001
       fade_distance FadeDist
       fade_power rgb < pow(Color.red,3),
                        pow(Color.green,3)
                        pow(Color.blue,3) >
     }
   }

#end


Note that I do usually use 1cm = 1 POV-Unit and in this case 
fade_distance 1 works pretty well. You have scaled your gem much
bigger so you have to adjust fade_distance to fit your scale.


Attached is a quick lo-quality (90 seconds) preview render - not a 
spectral one - featuring your stone: from left to right emerald, 
sapphire and amethyst.

-Ive

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