I agree with @testpilot Unless it's been left out in the weather for three decades, I’d be hesitant to take anything resembling sand paper to it. Pick up any metal polish (check the auto parts store) and combine with elbow grease and a bunch of old sacrificial T-shirts. They’ll turn black as you remove built up oxidation but the platter should shine up nicely as you hand buff it out. A light coat of automotive wax will keep it shiny for a long time.
