...can get it back to brass clor if you soak it in a solution of
ammonia or vinegar and hydrogen peroxide.
Make up another solution of PhDown (as if for pickling), then add
some hydrogen peroxide (the drug store type is good enough). Put
your brass into this solution, and it will remove the pink oxide.
Watch the metal to see that there are very tiny bubbles rising from
it. If not, add more peroxide. Gentle warming speeds the process, but
do not let it boil! Also, do not leave the brass soaking overnight –
the solution will etch your metal.
This is a process I call “bright dipping,” even though originally
dilute nitric acid was used. I think it was Bill, at Reactive
Metals, who came up with the use of hydrogen peroxide and PhDown to
accomplish the same thing, more slowly but more safely.