If you are referring to this kind of hubcap (not mine, just a random picture off Google).
Then I think they are either chrome or polished steel. I'm not sure how you would refinish them. I've tried chrome paint before and never had much luck. It always comes out as a glossy silver color - that doesn't look like chrome. It may be that I've been using the wrong brands, but I don't bother even trying any more. If I were forced to refinish one of these I might paint them as I'm not sure you can get the shine back short of rechroming, an expense that doesn't seem worth it given how many of these are on eBay at reasonable prices.
If these are what you are referring to, I think I have a set of these in pretty good shape buried in my garage. I got rid of the wheels they went to a long time ago. If you are interested PM me. You can have them for the price of shipping. If not, no worries - they've been in my garage for several years - they can stay there longer.
A.J.
1974 Fiat 124 Spider
2006 Corvette
1981 Spider 2000 (sold 2013 - never should have sold that car)