Here's an image of internal refraction. Bikermouse! You need watrer in those glasses! The water should have a different refraction as wel, for then you get intersecting crtitical angles, which gives you the nce reflection vs. transparency. If you make them right, like in a nicely cut diamond, the refraction will produce it's own reflective images, even thoguh there is no reflection on the material itself. See my previous post with that cornell box image and look at the glass sphere. There is some blue in it on the right side of the sphere, but it has no reflectivity. It is purely the refraction along with TIR that creates the illusion of the reflected image. Half of the light is reflected back into the sphere, while half of it leaves and hits your eye. there is an angle for each material that represents the cutoff of this effect, called the critical angle. If anything strikes shallower than the critical angle, it will be reflected back. You can see this if you look at the water from the bottom of a swimming pool. You can only see the outside of the water in a certain zone of vision (which happens to be circular) and outside that zone you are looking at the reflection of the bottom of the pool.