According to Wikipedia, Mental Ray's *Dielectric Physical Phenomenon* shader
"uses Fresnel equations to simulate reflectance and transmittance of light
passing through the dielectric interface, as well as using Snell's law to
determine the angle of refraction. In addition Beer's law is used to determine
absorption of rays passing through dielectric materials."

Well, after looking over some basic dielectric equations I came up with this
simple POV-SDL setup for the following basic dielectric material in POV-Ray. The
transparency and reflection of the material automatically tune themselves
according to the material's IOR value:

//------------------------------------------------------------------------------
// Dielectric Ball
/------------------------------------------------------------------------------
global_settings { photons { spacing 0.01 } }

#declare IOR   = 1.33;
#declare REFL  = pow(((1-IOR)/(1+IOR)), 2);
#declare TRANS = 1 - REFL;

sphere { 0, 1
   texture {
      pigment { rgb 0 transmit TRANS }
      finish {
         reflection {0, REFL fresnel on } conserve_energy
         specular REFL roughness 0.005
      }
   }
   interior { ior IOR }
   photons {
      target
      refraction on
      reflection on
      collect off
   }
}

With an IOR at 1.0 the object is completely invisible and reflectionless,
although I see some hint of a photon ring at the invisible sphere's base (so, a
dielectric material might make a good cloaking device, but just like in sci-fi
movies there'll still be the occasional photon ripples to give your position
away).

I found it really interesting that the transmit and reflection values changed so
exponentially, with very quick changes from completely transparent at IOR 1.0 to
50% transparent at IOR 5.83, but it took an astonishing IOR 8000 to get to 0%
transparent and become totally opaque! Regardless, I think the circular photon
ring contracting into a dissipating glow dot is a really cool effect. I'm going
to have to render an animation of this...

Cheers,
Rob
-------------------------------------------------
www.McGregorFineArt.com

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