Go back to Izzal Din, in the Jarsath Wastes ( -689, -108, -854 ) Copy/waypoint -689, -108, -854.
Izzal was amazed at the weapon that I obtained at The Tabernacle of Pain.
He explained that it is the reformed metal tablets that once held the tenants of marr, but how The Truth of Marr spent a detrimental amount of time within the demi plane known as The Sphere of Malevolence. As a result of that time, it has become corrupted.
He believes that there must be a way to cleanse the sword and restore it to its prior glory.