You can also use "lost wax" casting (or variations on same) with 3D printing: build the positive model in wax or similar material, plaster/sand around model, me

You can also use "lost wax" casting (or variations on same) with 3D printing: build the positive model in wax or similar material, plaster/sand around model, melt/vaporize positive material in furnace, and then cast into mold.