Welcome, Joseph! I’m sorry to say I can’t explain the magnetic
silver, but, for what it is worth, I’ve had the following
experience, which I’ve continued to wonder about.
I melted a bunch of miscellaneous scrap, and poured it into water to
make grain. Before melting, I went over it with a magnet to remove
possible residue from files and steel wool, and pickled thoroughly.
After melting, pouring, and re-pickling, I had the (dumb, I guess)
idea of tumbling the whole mess in steel shot to brighten it. I used
a strong magnet to separate the shot from the grain, and, to my
surprise, some of the grains were picked up by the magnet. I threw
those away. I’ve never checked finished pieces, though.