[Scarlioni]

I think the suggestion to modify the properties of bronze armor would match the game. My understanidng or bronze is as follows.

Bronze is made from copper and tin with some arsenic thrown in. In fact copper was alloyed with arsenic before tin. I believe this was because arsenic appeared naturally in/near the early copper exploitation. Tin almost is almost invaribly found separately from and usually a good distance from copper.

Bronze also enjoys the advantage of being able to be cast, and your forge doenst need to be as hot. In Dominions 3 terms I would think Bronze would be more expensive than iron because of the need fot imports, but would cost fewer resources due to the casting process.

I know less about iron. Involves hotter forges and much hammering, but since your working with only one element no expensive importing. As iron is repeatedly reheated (hotter is better) and hammered you start getting to steel, as in pattern welding.

In game terms I'd give the following modifiers to Bronze over the corresponding Iron items.
+1AP +1enc Costs more gold but fewer resources.

For small things like a cap there'd be no difference between iron and broanze performance wise. The word cap brings to mind "cheap" and "incomplete coverage" as well as "light" and "cheaply mass produced" so I'd say

I'd say something like a corthian style helmet would be more equated to a great helm.

Just my two cents.