Doom of the cracked shield is cast on a melee weapon. The next time that weapon is used, it destroys the target’s nonmagical shield or damages nonmagical armor, in addition to the normal effect of the attack. If the foe is using a nonmagical shield, it breaks into pieces. If the foe doesn’t use a shield, its nonmagical armor takes a -2 penalty to AC.    If the target doesn’t use armor or a shield, the spell is expended with no effect.