Dark Iron Bar

In order to learn the recipe to smelt Dark Iron Bars you must first finish a quest that involves taking some materials into [zone=1584], the materials needed for the quest are:

2x Star Ruby
20x Gold Bar
10x Truesilver Bar

The quest is called "The Spectral Chalice", which starts at [npc=9037], he is the second dwarf ghost to your right when you enter the Chamber of the Seven.

To reach the Chamber of the Seven, enter Blackrock Depths, then use the Mole Machine control which is to the right side looking from the entrance. Choose "Just past the Grim Guzzler", from there take the door on your right and just keep going downward, Chamber of the Seven is the room after a large metal smelting plant with lava golems patrolling in it.

Once you have learned the recipe, you can proceed to the Dark Iron Forge to smelt your Dark Iron Ore. To reach the Dark Iron Forge, proceed through the Chamber of the Seven (you will have to defeat the dwarven ghosts first, speak to [npc=9039] to start the boss fight), after exiting the chamber, turn right and head down the ramp to where you can see 3 fire elementals guarding a bridge.

Head left past the fire elementals and over the narrow metal walkway that leads across the lava, there you will find the Dark Iron Forge guarded by another fire elemental.

For everyone wanting to smelt Dark Iron bars, here's a little walkthrough;

Before you go in, make sure you bring:

2x Star Ruby
20x Gold Bar
10x Truesilver Bar

Upon entering use the transporter to transport you to the Grim Guzzler. Take the first right, past Ambassador Flamelash, past the golem trash packs, you should now arrive at "the Seven". Talk to Gloom'Rel to make him spawn the chalice which you can click for the quest. Hand in the materials and complete the quest. Afterwards talk to Gloom'Rel again to learn his "secrets", which is learning how to smelt Dark Iron bars. Next up, talk to Doom'Rel which should start the encounter. Kill all seven mini-bosses and proceed through the door, then make a right. Before the first trashpack make a left and proceed to the forge. Here you can smelt your Dark Iron bars.

Remember, it takes 8 ores to make 1 bar.

Good luck!

Dark Iron Bars require 8 Dark Iron Ore to smelt. The can only be smelted at the black forge. Assume you're looking at the bridge in BRD that leads to the entrance of Molten Core and the attunement shard. There is a short path off to the left. There is a black box looking thing. That is the black forge.

To craft most items that require Dark Iron Bars, the crafter will need the Black Forge. This is the black anvil constantly circled by Incendius in BRD. HOWEVER! Not all DIB items require said anvil, try a regular one first.

You'll notice most of the craftables are high quality FR items. One's best bet for decent FR without loss of stats is to make helm and pants and add +20 FR to each. The fewer items one must remove for FR the better.