Auxilia shieldbosses why "allways" brass??

[Folkert van Wijk]

Still there must be a reason why mankind moved from the bronze age into the Iron age. I always understood that iron/steel was tougher then bronze and also more difficult to work with. So iron was the "new" invention especially for the Celts who where the first Europeans that brought iron working to a higher lever. Therefore it looks to me that iron in those day's was more sophisticated then bronze, therefore more functional, yet more expensive and so in those days cooler to have then bronze. Yes I do like the shine of bronze more then the cold look of iron, but hey where from 2008 and not from around 0...