Take a look at the FTC regulations on how much solder is allowed to
be in a peice of jewelry. Only a very small amount is allowed,
though I’m not sure the exact amount because it’s not a strategy I
pursue. There are myriad technical reasons why one shouldn’t use
solder in casting alloy, but if you have to argue with them about
the merits of quality, you’ll probably never win out. However, the
threat of breaking federal law is a bit more compelling, even though
I haven’t heard of anyone getting busted over solder. Too bad, too.