In order to get the recipe to smelt Dark Iron you need to make sure before you go in the dungeon to have 20 gold bars, 10 truesilver bars, and 2 star rubies; then at the spot with the seven dwarf ghosts before you kill then talk to gloom'rel, he'll conjure a bowl click the bowl make an offering of the bars and gems and then talk to him again and your done. Also the only way to smelt is in the room with the fire elementals and instance to the Core, on the side there will be one lone fire elemental guarding a oven looking forge in the wall of lava and your done.