Ive got a bottle with interior faces set to one material ID and the exterior faces set to another ID. using a multi-subobject material with a vray glass material in both slots as instances it renders correct. when i set them to be a copy material (but with exact same parameters it renders really dark. im using fog in the material and this is whats causing the major problem.
Yep; it won’t work properly unless it is the same material (V-Ray would not know where the fog ends).
Best regards,
Vlado