Bronze was harder than copper and came to replace it in weaponry. It also had a bright, shiny surface—hence the simile in Rev. 1: 15.
Citation for bronze
Citation styles are based on the Chicago Manual of Style, 15th Ed., and the MLA Style Manual, 2nd Ed..
MLA
"bronze." In A Dictionary of the Bible. Ed. W. R. F. Browning. Oxford Biblical Studies Online. Jun 20, 2013. <http://www.oxfordbiblicalcstudies.com/article/opr/t94/e321>.
Chicago
"bronze." In A Dictionary of the Bible. , edited by W. R. F. Browning. Oxford Biblical Studies Online, http://www.oxfordbiblicalcstudies.com/article/opr/t94/e321 (accessed Jun 20, 2013).