Okay so the name is lame. Maybe it would be a cape, maybe armour. Whatever, this artifact is a Magical Armour. Is an inventory item.
Cost.... 10000g
Effect: Absorbs 50% of damage dealt by magic abilities. For example fireball, Spit, Pentinance. Pretty much all things that cause damage to a DG that ARE NOT reduced from normal armour would be absorbed 50%.