I remembered this from when my wife did stain glass. 1: take Ispropyl Alcohol and a tooth brush, not the one you use and scrub the track to make sure there is no oil on track, let alcohol evaporate. load parts in to ultrsonic cleaner
run through two cycles
remove parts and dry.in a small plastic cup or such add novacan plack Patina
be careful this is a chemical, acid when color is reached , which will happen quick rinse with cold water and let dry
the effect is a rustry black finish. try on one or two before you go with a lot of parts I got the Patina at stained glass store , they also have one for zinc I think I will try. if this has come up before sorry for waisting time, if not I hope you learned a new procedure.
Jim

remove parts and dry.in a small plastic cup or such add novacan plack Patina


Jim