These are a couple of animations when I was exploring how to age materials with rust, to give a pitted corrosion effect. Using Studio 3D Max 5 and simple textures - rendered with scanline. Strangely, most clients don't want to see rust - instead wanting pristine models ! So, these tests stopped here.

Rusting steel ball, using smoke mixmap and bump maps - use controls to play

Modified version of the rust texture acting on a chrome sphere - use controls to play