Here is an example for you, a red brass (85-5-5-5) boat horn which I
gave the sulfuric-peroxide treatment to:

http://www.shiphorns.com/3as.html

The pickling was preceeded by some Citristrip to get right of the white
paint blobs, and followed by a liberal application of Baldor buffer to
the shiny parts. Nevertheless, the chemicals did all of the work in
getting rid of the tough chocolate coating, and also the spots of the
various other copper salts (the green and blue areas). I could not have
simply buffed right through the brown oxide layer because the cast
brass is somewhat porous. I'd have been left with dark speckling from
pits that still had the oxides (that or a very thin horn! :-)

-Adam