Hi to the crowd,

some weeks (months?) ago I posted the geometry of the stone of orlov to the
p.b.s-f (under my now abandoned nick of TawnyOwl) and promised to investigate
the texturing of this special stone. Alain was so kind to give some advice and I
searched the newsgroups for other hints and found a material by Bruno Cabasson
which looked best among the published ones (some authors showed very fine
diamonds in the p.b.i. but gave no hint how they crafted the stones
unfortunatelly). In fact Alain and Bruno nearly proposed the same material.
There were only slight deviations in some parameters. That was really helpful,
since I only had to investigate this deviations. Many thanks to Alain and Bruno.

I played around with the parameters in animated sequences one after the other
and ended somewhere between both proposals. For example Alain proposed to use
"some reflection". So I started an animation which chanced the reflection step
by step and in the end I decided the physically correct value (amount of
incoming light=reflection + refraction) looked best. That should be so, but in
raytracing settings not exactly modelling physics can look better. A very
helpful hint by Alain was the use of an HDRI-Lighting which improved the scene
much. In fact the stone is at the table of Jaimes Vives Piqueres kitchen (since
I used his "thekitchen.hdr"). My main idea was to approximate a picture by Elkan
Wijnberg, which can easily be found with google, or better the caustics present
there to prove the best material. Since the lighting and camera position in the
original picture is unknown to me, I could only go for a similiar picture. But I
think I have achieved this goal.

Please excuse, that I didn't model the sceptre in every detail. The information
about it in the net is very limited. All other pictures I found were very small
in size and I have not the opportunity to travel to the Kreml this days to look
at the original diamond, unfortunatelly. But I wanted to have all the smaller
stones in a similiar position. For example I used another Saint Georg with the
inlay. I liked the version of August Macke, an German painter, most and his
copyright is expired since he is now 98 years dead.

I will thank Bruno and Alain for their help again, FlyerX for his wonderful
PoseRasy, Jaime Vives Piqueres for his kitchen, the unknown author of gems.inc
for his brillant57 (the link to the source is broken by now) and Peter Houston
for the blobman-hands. And of course Elkan Wijnberg for his picture and his
permission to use it for any purpose while mentioning his name.

Here is the material I finaly used, a parametrization and a slight modification
of Bruno Cabassons macro:
\begin{verbatim}
#macro M_Diamond (_color, _purety, _samples, _density)
    texture{
       pigment {rgbt <1,1,1,_purety>}
       finish {
#declare ReflValue=1-_purety;
          reflection { ReflValue fresnel }
          conserve_energy
          specular 0.8 roughness 0.005
          ambient 0 diffuse 0
       }
    }
    interior {
        ior 2.417 //1.51
        #if (_samples != 0)
            dispersion 1.044
            dispersion_samples _samples
        #end
        fade_power 1001
        fade_color _color
        fade_distance 1/_density
//        media {samples 1 scattering{1, 0.01}}
    }
#end

#declare MatDens=15/100;
#declare MatColor=<35/50,45/50,1>;

#declare GrossmogulMat=material { M_Diamond(MatColor,0.99,15,MatDens)}
\end{verbatim}

And here is the picture:

Best Regards,
Michael

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