Vitreous Focuser

Source
Obtained from at The Bulwark or  in Chillwind Camp. You must have one of these in your inventory in order to loot Osseous Agitators, Somatic Intensifiers, and Ectoplasmic Resonators from the mobs at the various cauldrons in Western Plaguelands. These can then be used at the cauldrons to complete a repeatable reputation quest for the Argent Dawn.