What I used was some kind of metal etching solution. My friend poured some in a jar and gave it to me. I don't know the name of it but it is a green colored liquid. I would wipe it on the metal let it dry for a little while then wipe it off. The metal would be super smooth before I put it on but after wards it had a rough feel to it. You more than likely can Goggle something up that would work or go to your local auto paint supply and they will have it. I think as long as you use exposy primer you should be fine but I did both just to make sure.
