I am trying to make a procedural rust material for cycles. I am using a noise textures node going into a ColorRamp node with the color stop set to constant. I am using 2 color stops. This produces two colors on my object. I am then adding additional colors (using the same technique) to the object using a Mix shader node. This mixes the colors together and creates new colors. What I want to do is add materials on top of existing materials without mixing them together. Can a procedural material be added on top of another procedural material?
Rust should be treated as a dielectric material (like wood, glass, or plastic) instead of a metal. Therefore all the “shading parts” differ greatly from the metal underneath. What you want is two completely separated setups in your material - one for the metal and one for the rust, and blend (quite sharply, normally) between them using a Mix Shader node.
Then access bumps using normal inputs for each, rather than trying to go the quick route and use the displacement input on the Material Output node. You then get metallic scratches or whatever effect you’re after for the metal, and rough irregular bumps for the rust.
This will not answear your question but I post in in cas it can help you.
The best procedural rust I have seen was in poser. The guy made a tutorial about it and I was able to reproduce the logick in BI at the time 6 year ago. I can’t do it in cycles but I just restarted using blender so you may have more chance than me with it.
http://forum.runtimedna.com/showthread.php?45871-Inside-a-Material-01-Rusty-Pitted-Iron
this is a quick approximation I made…it’s not quite the same, but you might be able to work with it…
(edit) oops, just noticed you wanted this for cycles…gotta watch that, hehe. hopefully it helps anyway.
(edit) had to fix the awful lighting, haha…
rust2EXP1.blend (1.91 MB)