I have done quite a bit of research on what sorts of helmets were worn by imperial Roman soldiers and it seems that both iron and bronze were used, with iron predominating over time.
It seems, however, that there’s no real clear benefit to one or the other. Iron is cheaper,, but needs to be wrought, which increases cost and complexity. Brass is more expensive, but it doesn’t rust and can be cast.
Since I am building a 3mm Roman Imperial army, I need to visually distinguish units as much as possible. Would it be too much of a stretch to paint my auxiliaries with bronze helmets and the legionnaires with iron? I know that in reality, both groups would probably be mixed, with iron predominating.
But my rationale here is that, given that auxiliaries were more “jack-of-all-trade” troopers, they probably had more need of rust-proof brass helmets than the legionnaires.
Practically, this will allow one to distinguish them from legionnaires on the table when looking from above and behind, given that both troops have the same base size and number of ranks.
What do you all think?