Speak with Derotain Mudsipper at Gadgetzan in Tanaris.
Description
There's a dwarf in Gadgetzan by the name of Derotain Mudsipper who'll teach you how to make imperial plate armor. All you gotta do is get to the Tanaris desert and find him. Interested?
Completion
Of course I'll teach you how to make imperial plate armor! It might cost you a bit of gold... in the form of thorium bars!
Additional Information