planishing helmets

[richsc]

I'm taking a metalsmithing class with the goal of raising a helmet in one piece (it's going to be red brass for now). Having spent an hour or more planishing out a small brass practice bowl, I am really wondering if Roman helmets would or could have had this level of workmanship, particularly considering the much larger surface area. Polishing with rough grit could have wiped the hammer marks out, but have helmets been found that have obvious planishing marks over the entire surface?
All the helmets reproduced today are extremely smooth, which is not easy to accomplish, apparently.