One worthwhile process on any piece you can take off & isolate is to simply boil it for a while in water. This will help loosen any free rust & convert that which adheres to black, thus enhancing the color. A rub with 4/0 steel wool & oiling will in many cases be all that's necessary. Be sure & use good water, same as for bluing. This may not retain as much "Patina" as you might want, but Patina is not original. Oft times it is hard to preserve patina without risking "more patina" build up.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra