To cast this spell the Mage must take the life of a single Keldian in ritual sacrifice, plunging a ritual blade into their heart. As the sacrifice dies it takes some of the Mage's corruption with it, sloughing it away with the flowing blood. The Mage loses corruption equal to the Spirit of the sacrificed Keldian. The 1 point of corruption gained for casting the spell is permenant however.
In desperate times the spell can be used to sacrifice an animal instead of a Keldian. In this case the corruption lost is equal to the creature's Intelligence or the Mage's Level, whichever is lower. The casting corruption is still permenant.