As far as I knew, the normals on refraction diagrams were depicted perpendicular to the surface. "That's why there is no Refraction Channel for volume materials. Because refraction is not a volume property." Well you're right and wrong here. Refraction is in essence a property of a volume. If it were not, then refraction would simply not exist. Refraction in the real world needs a solid medium to travel through. Take glass for example. If glass were only a minutely thin shell with glass - air - glass then refraction wouldn't occur... This is not true in bryce because 3d objects are in essence shells. Because of this bryce has to cheat. It takes the theory of refraction and applies it to the outer surface of an object. I think most applications do this as well. "" An increase in the refractive setting, now the cube is casting a shadow." Yes because you are making the optical density denser. So the cube lets less light in. and cast a shadow with the light that does not penetrate into the cube. The denser the optical properties become the less light is let in, thus the spherical shape gets small as less light travels through the cube and exits out the rear." Also not true... A more refractive material appears darker because of the way light is being bent at the surface of the material itself. Because light is being bent so much when it strays from entering the material at a perpendicular angle there are less incident 'light beams' interacting with all areas inside the sphere/cube whatever. Subsequently there are also denser areas of 'light beams' inside of the sphere because of this. This is not due to less light penetrating the surface. This is caused only by hightened opacity and reflective properties.