Iron Rivets in a Brass Umbo?

[Matt Lukes]

When you consider that things may have been re-used, bits replaced, etc. over the years, there's every reason to believe somewhere, sometime iron rivets secured a copper alloy umbo to someone's scutum. Just as an example, I have a small copper alloy buckle that has what appear to be several new holes in the plate for replacement rivets- the final one, which is still in place, is iron.

Matt