Smelt Dark Iron

Ok here is a very detailed account of what to do to be able to learn the ability Smelt Dark Iron. I am creating this one detailed as possible because it is annoying to get bits and pieces by reading through several posts to get all of the info needed.
1. Before heading to Blackrock Mountain to go into Blackrock Depths you should gather these items in these amounts for the quest Spectral Chalice.
Gold Bar x20
Truesilver x 10
Star Ruby x 2
2. Next you head to Blackrock Mountain to go into Blackrock Depths.
3. Once inside the instance Blackrock Depths, turn to your right and you will see a bullet like drilling machine(aka digger) sticking out of the ground. When you click on it choose the option "take me just past The Grim Guzzler". When you load back in from taking the digger there is a mob, after the mob you will turn right, go down a flight of stairs, turn right again and bypass Ambassador Flamelash by turning left in his chamber. Follow the little hallway to the Mold Foundry, once in the Mold Foundry you will follow the room around to the right where you will enter the Summoner's Tomb.
4 . You will speak to Gloom'rel which is the second dwarf on the right upon entering the Summoner's Tomb.
5. When you speak to him you will ask him to tell you all his secrets and he will summon the Spectral Chalice to the right of him that will have an exclamation indicating a quest. Pick up the quest and if you have brought the above mentioned items you will be greeted with a lit up question mark signaling you are able to turn it in.
6. Be sure you speak to him again after you have turned in the quest and you will tell him "I have paid the price now tell me your secrets" and he will grant you the ability to smelt Dark Iron.

When you get or have already acquired the Dark Iron you wish to smelt, then you can talk to Doom'rel to start the fight and kill the seven to get the door to open. Once you have gone through the door there is a door to your immediate right that leads you to the bridge that takes you to the Molten Core. To the left and just before the bridge is a set of train tracks leading to where you actually smelt the Dark Iron.

The alternative to killing the seven to get past the door, is to go back to Ambassador Flamelash and there is a place to jump off and try to swim through the lava. I personally feel that if you are doing this at a level that you can just run through the mobs anyway why not just kill them real quick instead of swimming through lava. But to each their own.

Hope this helped!

You get this quest by talking to Gloom'Rel, one of the seven dwarves in Blackrock Depths. He will ask for a tribute so remember to bring:

2 Star Ruby
10 Truesilver Bars
20 Gold Bars

He will tell you to put them in a Spectral Chalice. Don't forget to talk to him again after you have done this.

If you delete Mining to learn an another craft, and after that you decide to re-learn Mining, the tribute is considered to be payed once and for all, means he'll give you Dark Iron smelting free of charge.