She’s probably making a vulcanized mold from the ‘first round’ silver
piece. Brass/bronze react with the vulcanizing rubbers and give a
slightly cruddy surface to the mold walls, while silver doesn’t. When
I was doing a lot of production work, I did the same thing: rough it
in wax, cast it in silver, then clean the silver so that it’s
perfect, polish & etc. Then make a mold, and cast it in the final
metal. Doing it that way lets you get a much crisper look than you’d
normally get by going straight from wax to the final casting.
It’s partly a factor of what material the person is most comfortable
working in. Some people work on nailing the wax, and go from there,
some people (like me) would rather get it into metal where we can get
our hands on it, and then clean it up. Having it in metal also lets
you do things like soldering on sheets, plates and wires, in ways
that (to my mind) are much quicker than fussing with trying to fake
it in wax. But then again, I’m a metal smith, so it stands to
reason that I’d prefer metal to wax.
For whatever that’s worth.