Hi, I got a curious effect when set polishedbackpainted finish and unified model for optical surface. Sometimes photons are reflected with random angle though the chosen model implies only plain reflection, either Fresnel reflection at the boundary or reflection from the paint. I think I found places in the source which cause this: G4OpBoundaryProcess.cc: lines 547 and 621 where reflection from boundary is considered. "if" statement checks only for polished type and omits polishedbackpainted case. As a result Lambertian reflection is chosen.
Turns out, 'polishedbackpainted' works just fine for me. Please note, although it exists as an option, 'polishedbackpainted' really does not provide extra functionality and the result should be exactly the same as 'polishedfrontpainted'. In both cases, the reflected ray obeys (v_incident + v_exit) dot normal = 0.
