I get most of my silver and silver/copper items bombed by a large jewellery manufacturing company. Wouldn't dare to do it myself! It gets rid of all the firescale magnificently.
It might be worth your while getting in touch with a similar company as it is likely that they will be bombing each day. It costs me just pennies to get it done.

Unfortunately I've had no experience with bombing other metals but once bombed that's when you need to do the polishing. The process does make copper very bright but once polished and finished the colour is warmer.

Hope that this is of some help, Ally