Creatures using natural armour or wearing armour made of metal, stone, or wood must also make a Constitution saving throw. On a failed save, their AC is reduced by 1 until the spell ends, as corrosion eats into their protection.
At Higher Levels: When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d8, and the AC reduction is increased by 1, for each spell level above 3rd.