Vitreous Focuser

Source
Obtained from Apothecary Dithers at The Bulwark (Horde) or the Alchemist Arbington in Chillwind Camp (Alliance). 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.

Note
If you accidently throw this item away you can get a replacement.