I use a spray on product for removing rust that contains phosphoric acid. I spray it on and let it work for about one hour then wipe it off with a wet cloth that I soak in a baking solution then wipe it down this time with only a wet cloth then dry the part and wax it down. Navel jelly also works. This finish is all gray looking if you want a splotchy look then use a cold blue solution and rub it back lightly with an abrasive pad or 4/0 steel wool.