Now You're Cooking with Netherlight

To unlock the Netherlight Crucible you have to play through the Argus story campaign and reach the quest An Offering of Shadow at the end of Chapter 3: War of Light and Shadow to complete Now You're Cooking with Netherlight. (This won't unlock until 3rd week into Patch 7.3.) (Criteria: Complete the quest, "The Netherlight Crucible". - Imbue a relic with Netherlight Fortification using the Netherlight Crucible.) Unlocking the Netherlight Crucible is account-wide, once you unlock it with one of your character your other characters can access it too.

How is this unlocked?

@Jakemiller75 : "Unlocking the Netherlight Crucible is account-wide, once you unlock it with one of your character your other characters can access it too." That's not entirely true. Once you unlock the Netherlight Crucible, it will be unlocked for your other characters on that server; not account wide. Meaning that if you're on Vek' and you unlock the Crucible, then change over to Nes, none of your characters there will have access to it until a character on that server also goes through the Argus story campaign.