Removing Lead Solder From Gold Coin (2nd try)

(I tried posting this last night from home, but was probably stymied
by the fact that I have changed my system date to prevent W7 from
crashing. Apologies if this is a repeat.)

On another list I read (about coining), someone asked if it is
possible to remove some lead solder from a gold coin. I thought of
using an acid that would dissolve the tin and lead, but what would
that be? Also, would any such acid leach out the alloying metal from
the gold, and would that change the color of the coin?

The coin is a 2 1/2 dollar US piece, in otherwise good condition, so
abrasive removal would probably not be a good option.

I'm not involved in this, but it seems to be an interesting problem,
and if anyone has a workable solution, I'll be glad to pass it on
(with attribution) to the OP.

Thanks,
Joe