This large smith's hammer appears well-used and rough in make and maintenance. If you use this hammer as part of a set of smith's tools, you can repair metal items in half the time, but the appearance of the item is always sloppy and haphazard. When you roll a 20 on an attack roll made with this magic weapon against a target wearing metal armor, the target's armor is partly damaged and takes a permanent and cumulative –2 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.