Metal that's been polished until it shines is burnished. If you're a fan of knights, you might enjoy checking out the burnished suits of armor in a museum.
Burnished metal is so smooth that it's almost glossy — light reflects off its surface. A brand new car and a gleaming piece of jewelry both have a burnished look. To achieve this effect, a metalsmith has to burnish, or polish, the metal. You can use this adjective figuratively too: "He revised that book report until it was burnished."