A promethium bar is a bar of refined Promethium ore. It is the highest tier of bars available in Daemonheim, with the highest level requirements to obtain and use. It can be created through the Smithing skill by using promethium ore on a furnace, requiring level 90 Smithing and granting 63.7 Smithing experience. The promethium ore itself can be mined from the rocks scattered throughout the dungeon, obtained as a monster drop, or bought from the Smuggler.
A promethium bar can be smithed on an anvil through the Smithing skill to create Promethium equipment, granting between 91 and 95.5 Smithing experience per bar used. A list of promethium items that can be smithed from promethium bars and the Smithing levels required can be found here.