This is clearly a clear coat finish:
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Polishing would remove the uneveness in the finish, presenting a perfectly smooth look rather than the slight orange peeling that you see.
Colour shots from the movie, take these shots to a professional painter and ask how to match this and they will say 'clear coat', and give you a funny look for asking something so obvious.
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Looking at Gino's shots of his own helmets, they look clearly polished. The finish is flawless and I'm sure a TON of work went into getting them like that, but they do not line up with the images I've posted.
A polished black without clearcoat is a lot deeper black and shiny.I know a guy who ripped all the clearcoat from his car because the black is so much better without clearcoat.
And you must look at the gunmetal sections..they are a lot more semigloss as the black ones.You can see that very good on your pic who Kershner wants to kiss Vader.You must also see the movie lights on the scenes you posted lower.
In the same scene(and different lights)the helmets looks not more so shiny.