Ray Index of Refraction

All dielectrics have Index of Refraction property (IoR) that affects how it reflects light. For transparent materials IoR also dictates refraction direction.

If you submerge a dielectric into a liquid, it's relative IoR will be smaller - both reflections and refraction will change, submerged dielectrics become less shiny and look less dense. This affects all liquid-solid interfaces. E.g. wine in a glass doesn't reflect light as much, droplets reveal surface they are on. Of course, some of these effects can be implemented by using dynamic paint or booleans, but it is a huge pain in the s and doesn't always work as expected.

I suggest that IoR of the last bounce should be recorded for each ray and exposed in the Light Path node. As an option, Cycles should also divide IoR of the material by the ray's IoR to follow the physics, so that artists wouldn't have to worry about this in their shader code.