Try this at your own risk. When I get a gold peice with lead
solder on it to repair, I remove it but soaking in warm muriatic
acid overnight. I also put a pinch of red rouge in. I warm up the
acid until almost boiling put in the pinch of red polishing
compound,remove from heat, put under a vent hood for the night.
You can see the lead fizz and beginning to disolve right away. In
the morning the lead is black and crusty and comes of easily and
completely with a file. I got this from a very old jewelers and
watchmakers formula book. It has always worked for me on gold,
never tried on silver. I usually charge 25-45 bucks plus the
repair for this because not many know how to do it and just say
the piece is ruined AND because the fumes are so bad I hate to
do it. People are always thrilled to have their items restored
the way they should be.