Just completed my first Vault w/a clanmate. Great success. I collected about 67 Decayed Eldarium & had no idea what to do with it. On a whim, I put a few pieces in the furnace. Voila–Eldarium bars! I clicked on the Info button (because I love all the lore entries on stuff) and saw a reference to using hardened steel with the decayed eldarium. Problem is, I didn’t use any. I didn’t use anything. Furnace + coal + decayed eldarium = eldarium bars, while the flavor text specifically references using hardened steel with the decayed eldarium.
I shouldn’t be working to make things harder for myself, but either the decayed eldarium → eldarium recipe is broken, or the flavor text on the eldarium bars is wrong.