"Imperfection is the digital perfection" --unknown

The CG world is so clean and artificial looking that you need to bring in the uglies of the real world to make it look real.

Stuff like dirt, grime, scratches and rust. All of which is covered in this tutorial :)

It took me a couple of weeks of experimenting, but I finally nailed down the perfect method for creating rust in blender (without any extra software)!

Final Image