Where does it go? Metalness vs Roughness

Spur

Hi everyone. The team I work with has recently started transitioning to physically based rendering. So I've been going back to some older assets and adding in MRAO maps and testing them, especially for bare metal stuff. Everything seems to be working well but I am a little confused on is where to include weathering. In metalness or roughness or both? I would say both. So would it be the same weathering layer in both metalness and roughness? Metalness indicates what is metal/conductive or nonmetal/insulator. It would be my thinking that weathering would be in the metalness map just as paint is since that is diferentiated as nonmetal. Rust would be nonmetal just as paint. So would dirt, oxidation, etc. So those areas would be mostly black minus a few areas that might be transitioning between paint/metal, rust/metal.

Roughness would purely be the surface properties, such as smooth chrome or rough cast iron. But what confuses me is that weathering can contribute to the roughness as well. A smooth surface with rust would have high roughness in a rusted area. So would it be correct to include the surface weathering in both the metalness and roughness.

Any tips or thoughts on the above?

AlecMoody

It is specific to what kind of weathering you are trying to create. Metals corrode and oxidize, and in the process they undergo chemical changes. Also, many kinds of damage and localized wear include a component of surface transfer between materials. Do what looks right for the circumstances you are trying to replicate and don't spend much time worrying about what is technically correct.

Another way to imagine it, a purely roughness based wear method is limited to what you can do to a piece of metal with sandpaper and polishing compound. For example, look up cast aluminum and polished aluminum images. Neither of these extreme examples of possible aluminum roughness encompass what you will see with something like galvanic corrosion. Also, metals are porous (especially rough, corroded and rusted metals) and they take on a lot of contaminates which are often non metallic.