Derotain Mudsipper is a Thorium Brotherhood NPC in Gadgetzan, Tanaris. He gives the Imperial Plate quests: you hand in Thorium Bars and get the Imperial Plate plans. He sells nothing.
He is outside near the anvil and the forge, near the southern exit of Gadgetzan, next to the blacksmithing trainer. (51.5, 28.6)
Tanaris
Derotain Mudsipper
Imperial Plate quests
All seven quests need level 50 and are open to both factions. Each one asks for Thorium Bars and rewards the plans plus Thorium Brotherhood reputation. Do 
A Blue Light Bargain first, it unlocks the others.
| Quest | Thorium Bars | Reward | Reputation |
|---|---|---|---|
| A Blue Light Bargain | - | opens the quests below | 100 |
| Imperial Plate Belt | 20 |  Plans: Imperial Plate Belt | 100 |
| Imperial Plate Bracer | 20 | Plans: Imperial Plate Bracers | 100 |
| Imperial Plate Shoulders | 20 | Plans: Imperial Plate Shoulders | 100 |
| Imperial Plate Boots | 40 | Plans: Imperial Plate Boots | 150 |
| Imperial Plate Helm | 60 | Plans: Imperial Plate Helm | 200 |
| Imperial Plate Leggings | 60 | Plans: Imperial Plate Leggings | 200 |
| Imperial Plate Chest | 80 | Plans: Imperial Plate Chest | 200 |