Bronze bars are there as a permanent potion so you can bank your gold in them, instead of defence pots, which can be burned
You get them then you sell them... simple. They are not something that you use like the Mage, just you get gold from it. Info about Bronze Bars: You buy one for 30mill and sell one for 22.5 mill. A bronze bar was just a way to bank your gold, even though you lose gold in the end. It helps during war, or if you are being farmed. Or if you just don't want gold out but want to be able to get some back when you need it. Advantages: You can sell them for gold Earn them from Epics Banking Disadvantages: You lose gold Can only get dropped from Epics not wars Need a lot of them to do anything (Upgrade)