Posted with permission!

This surface works best when objects and/or polygons are connecting. The gritnode nodal-plugin works that way and thats where the "rust" is going to be based. That is why in the preview-image here we have put the ball inside the cube.

A rusty metal surface (using nodes) for LW9.x - This surface requires a free plugin (ee_GritNode) to work - Click here to download it.