Rust: Metal or Non Metal?

sbiswas

Silly question, I guess . Is rust metal or non metal? I mean should I paint rust as white or black in metalness map? Could you help me out by posting any reference link(s)?

Thanks for the help!

Der Hollander

Depending on the level of oxidation, rust should be black in your metalness map. If you have partial or spotty oxidation, then adding some gray in the mask where the metal is present is advisable.

passerby

its a non metal

Vailias

Black. Without getting too technical, metalness essentially means "should the color of reflected light match the diffuse color map?"

Things like gold and copper reflect white light as gold and copper due to their internal atomic structure. Most metals, or conductors also do this, but most other metals are "white" metals. They should still have a high Metalness in a shader.
Just about everything else doesn't. Rust reflects the environment as it is, Its also very rough at a molecular level, so it doesn't shine like the metal its an oxide of so its harder to tell. Also on rusted white metals, the color of the highlight won't even change (much).

This is a good example.


Notice how the brightest highlights on the bluegreen rust are white, while the highlights on the copper portions are pink? This is shot under white light. The whole thing is quite rough, so you're getting more "regions of highlight" rather than reflective points, but the physics still stands.

More info:
The actual color shift in metals is due to them being conductors, rather than dielectrics or insulators. Rusted metal is oxidized. This totally changes the nature of a metal. The oxide compounds are actually insulators, and so the "metallic" properties of color shift and luster isn't preserved.