I use Shapeways, too! I started a small jewelry company (= just me) this
past January and am bootstrapping it all myself — I just don't have the
funds to pay my casting house to hand carve the castings I want to make (or
to pay the milling fees if they print the wax from CAD files themselves).
I'll work through designs in plastic first, then in brass as my proto
model. I'll file it down/add texture myself, then send that piece off to my
casting house to use for the mold. I also recently started working with an
experienced jewelry CAD artist through Shapeways to help me make pieces
that are beyond my own skill set (the process was super easy).
Shapeways prints it in wax first them makes their own mold, and it's a
bummer they won't let you keep their molds. I also find that their brass
and castable wax are somewhat brittle, so if a design has prongs I can't
just print a one-off with them in brass because the prongs are too brittle;
I always need to make the mold with my casting house and have them cast it
for me. Their wax is hard to file without breaking it, so once a design is
ready I'll print it in brass or silver (if it's affordable enough) and make
final tweaks then.
So excited to hear this is opening up new design opportunities for you!
Good luck as you dive deeper