Early in my career I worked for a company that made costume jewelry.
The alloys used were composed primarily of tin with lead and
antimony, and perhaps some other metals in very small amounts. I
would have to say that I can’t recall anything being designed with
repair in mind. EVER. But then again some of the rings were going out
the door at $3 a dozen.
A soldering iron is appropriate. The time and expense of ramping up
may not be cost efficient, however. You can’t laser weld, sparkie,
torch solder or Puc weld this stuff, for the most part. The stones
are glass, foil backed, and glued in. The metal sags, and then melts,
often right out from under the plating. You are guaranteed to wake up
in the middle of the night in a cold sweat over destroying grandma’s
worthless trinket. Probably she will want the repair for far less
than the piece originally cost, after you have totally reconstructed
it. It probably cost $2 new, retail, unless it carried the made up
name of some imaginary designer, in which case it could be a valuable
"collectable"…
But someone has to do it, so, far better you than me. If you are
going to specialize in repairs, gold or platinum is a far better
choice, IMHO. Sometimes it even pays very well.
Rick Hamilton