Here is some rust I made from steel wool. The stuff in the foil is mixed with water so I could brush it on.
I know this isn't a model railroading forum but here it is "painted" onto a railroad cylinder car.
I did this as an experiment. But it was alot of work. It does add a bit of texture. You can get the same effect with rust colored paint and pastels added to the paint when it is still tacky.