Tae- I would suggest that a magnetic pin finisher would be the best
choice. Your material is soft and the pins are not abrasive so you
could get a fairly good finish with them. If they are rough, you
would need to have some very mild abrasive finish. I've had some
recent success with the wet disc finish option that runs on the
magnetic tumbler so you would still need to buy only one machine. The
disc options are relatively inexpensive. For fine gold, I'd use a
light weight very fine abrasive in the 3 micron range.
If you are looking for a high polish, the same machine can do a
final finish with the dry disc adapter. An alternate that would work
harden the gold would be to use stainless steel in a rotary tumbler.
If you have more questions, please post.