Question on rust.....

What are some good ways to model it?? I know there is some stuff you can buy that you apply in stages to create the look of it....but is there a way to do it using household stuff?? I looked over a rust spot on my wife's car to get an idea what I need-- I have some rust enamel paint-- but want to give it some texture. I was thinking of flour....but maybe that might end up becoming pasty? Any thoughts??