From an ior include file I found once (I forget where):

#declare Sapphire_IOR = (1.76 + 1.78) / 2; // A variety of Corundum
#declare Sapphire_IOR_Dispersion = 1.76 / 1.78;

As Chris stated, your dispersion is way too high, this number represents the
ratio of violet/red  IORs for the material. (The numbers in the declare
above may be inverted.  I can't remember anything from physics about
wavelengths and such. Anyone else?)

-tgq

"Sylvax" <syl### [at] darthsylvaxcom> wrote in message
news:3b8bea49@news.povray.org...
>

> 3B8BE104.266CDA51@gmx.de...
> >
> >
> > Sylvax wrote:
> > >
> > > 2048 x 1536
> > >
> > > 3 days on a 800 mHz Duron
> > >
> >
> > Sounds fairly slow for without photons, dispersion seems a bit
unnaturally
> > high, what value did you use?
> >
>
>   interior
>       {
>          ior 2.4
>             dispersion 1.70
>          disp_nelems 10
>
>       }
>
> I tried photons mapping... I gave up quickly!
>
>
> > BTW, Povray 3.5 will have ior and colors for sapphire and other minerals
> > defined in the standard include files.
>
> good news. I am a newbee with pov and it seems to me very difficult to
> simulate mineral looking.
>
>
> >
> > Christoph
> >
> > --
> > Christoph Hormann <chr### [at] gmxde>
> > IsoWood include, radiosity tutorial, TransSkin and other
> > things on: http://www.schunter.etc.tu-bs.de/~chris/
>
>

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