A number of years ago I had a pistol barrel in the white that I buried in a bed of table salt for a couple of weeks. It came out a very pleasing mottled grey color looking like it had aged for decades. If you do this just be sure to file/polish it to the degree of smoothness you want before 'salting' it. After the treatment you might want to rub the barrel with a cylinder wrist pin to harden the surface.