Corrosion

By combining the disciplines of water and earth, a mage of both can create a slurry of corrosive minerals to be flung at an opponent. Should this spray land on any metal equipment, it will begin to rapidly weaken and corrode it. If proper care is taken of the equipment, ultimately no harm will come to it; however, should a piece of armor stop a blow while under the weakening influence, it may crumple into uselessness. Weapons are less-immediately vulnerable, but will nonetheless deteriorate far more rapidly if used while coated with these minerals. It is rumored that the spell was originally commissioned by the guild of blacksmiths in an attempt to drum up business; whether true or not, there is no doubt that the working is effective.