> clipka wrote:
> 
>>> Maybe that's a part for media, not pigment.
>>
>> Birefringence is definitively neither a media nor pigment thing, but a 
>> straightforward interior thing, and would have to join ranks with ior 
>> and dispersion (as a matter of fact it's a difference in ior depending 
>> on polarization with respect to the "optical axis" of the (AFAIK 
>> necessarily) crystalline material).
> 
> How hard would it be to implement birefringence ...? Seems like it could 
> easily be faked
> 
> Syntax would be trivial:
> 
> ior 1.5, 1.7 //(birefringent material)
> 
> You don't really need to care about the polarization of light, since 
> light in POVRay doesn't have polarity anyway.
> 
> I would imagine tracing a second ray at a different IOR would be rather 
> simple to add.
> 
In addition of the second ior, you also need an axis or "direction".
If you take a sphere of birefringent material and make it turn, the 
difference in refractions changes. It also changes depending on the 
distance from the view axis.
There is a plane where both iors are the same and an axis where they are 
the most different, usualy. They are frequently perpendicular, but I 
think that there are cases where the axis is not normal to the plane...

I think that you "may" attempt to simulate it. Some experimentation in 
view. Some layering and/or averaging would be required.


Alain

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