Richard, The answer to your question can be complicated. It really
depends on what type, thickness, and style of metal you're tumbling,
what type of media you're using in the tumbler, and how long you're
tumbling. I routinely tumble my sterling pieces (even the very
delicate ones) in steel shot with burnishing media to work harden
them. I tumble them for about an hour (sometimes less), and don't
have any loss of detail.
However, if I were using a softer metal (like fine silver, or 24k
gold) or a more aggressive cutting medium in my tumbler, this would
not be the case.
Tumbling CAN be a wonderful addition to your finishing process, but
you do need to know more about it to decide which pieces are suitable
for which medium.
Best of luck!