Micro Seki gunmetal platter

One of the attractions of MS turntables is their gunmetal platters. Often these will show wear and tear of three decades.

What platters are interchangeable? Is there a film on the metal or is it patina? How did the platters present when new? Were they brilliant or dull finish?

Finally has anyone had experience in restoring a platter removing light gouges or uneven colour?