in news:3cf5f533$1@news.povray.org Tom York wrote:

> I could make an opaque material with an IOR and apply the
> Fresnel model to it in POV, couldn't I?

Yes

> It'd render faster and be more
> realistic (unless you were really dealing with ceramic tiles).

No

In 'daily life' it is assumed that transparent materials have an ior and 
opaques have not. From a physical point of view this is not true, all 
materials have an ior. The thing is that the refractive index is a 
complex number. For transparent materials the real part of it has much 
bigger influence than than the imaginary part, so the latter is usualy 
neglected in calculations. For example for metals the opposite is true. 
The real part of the refractive index has "no" influence.

POV-Ray only uses the real part of the ior in its model, so adding an 
ior to a metal would result in an unrealistic reflection.


Ingo

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