This time we’re taking a look at the quest Mysterious Machinations, which has you gathering three unclean metal skins. You’ll likely need to play a mission several times before you can gather them and turn in the quest.
Unclean metal skins can be found by killing and purifying frostcrawlers.
To farm unclean metal skins for the quest, I played the mission armor busters in Chapter 4 which requires you to kill five crawlers. The mission takes place in the Age of Yore.