How does one do this without an airbrush, and without making it look stupid in the process? I've seen some people using some thinned black paint and just.. drag it out with a brush. This looks like crap to me. There must be some other way for us brush painters. I've found a good picture of exhaust stains on the side of a Hurricane with the help of the awesome BoB movie from 1969. I would like my Hurricane's stains to look similar. I assume the grey part is really old, while the black is fresh. So. How?