The Corrupted Bar is a mineral bar in Avalon. It is crafted from 7 Corrupted Ore at a Caesium Forge. Corrupted Ore will spawn in your world upon the second defeat of Cataryst. In the world, Corrupted Ore appears as a navy-colored ore. It is pictured at right.
It's also worth noting that for some players, Corrupted Ore may spawn on the first time of defeating the Cataryst.