Hammer of the Armoursmith
An old blacksmiths hammer with a precious gem placed in the head.
This weapon does damage as a mace and is considered as such for all intents and purposes.
Upon hitting a creature wearing armour that primarily consists of metal (eg, chain shirt, half-plate, full-plate), that creatures AC is reduced by 1 as the armour is damaged.
In addition, any time spent crafting or repairing primarily metal armour using this hammer is halved.