It is machined at the Shubb shop in Missouri, and left unplated. Plain, unplated brass will darken in time. For those of us who appreciate brass, we prefer this look; reminiscent of an old microscope, or a piece of gear from a sailing ship. But if you like your brass to shine, it can be polished with a cloth and most any commercial metal polish, and it will shine like gold.
A good choice for instruments with gold colored hardware, and a natural for those who fancy a retro look.