Bill -- Don't know about aging, but I do know that iodine does an excellent job of browning, if slower than the more commonly used browning chemicals. My early barrel brownings were accomplished by coating a "white" barrel with iodine, then suspending the barrel over an elongated container of water and covering with a plastic "tent" to keep the atmosphere moist. Repeated applications of iodine deepened the browning, 0000 steel woolling gently between applications.