Dielectrics with Beer's Law.
Dielectrics and Beer’s Law are now integrated into the materials and environment frameworks. In the picture above the indices of refraction increase from left to right.
I have been working on dielectrics lately.
Glass sphere
This has uncovered bugs in my overall path tracing code, and more specifically in the way lights are sampled and their contributions weighted. I have had to put lots of efforts into fixing them (well, finding them first) and I am not yet fully convinced I have, especially regarding the way intersection with a light source following a specular bounce is handled.
Note that I have not yet implemented Beer’s Law: The sphere’s colour is just the result of absorption at the interface.