Metal made from the world of The home of the Darkness. More. It has the strange properly of absolutely no reflection of light. Any light that touches darkiron is absorbed, turned into heat, and dissipated.
As it doesn’t exist anywhere outside Umbra, it’s very expensive. Armor made with threads of Darkiron is worth a king’s ransom, and has the benefit of deflecting or severely weakening any spells involving light (e.g., fire spells).