From the Elemental Weeping Weapons quest introduced in the Visions In The Darkness event.

Acidic Elemental Pool
Acidic Elemental Pool
Value: ???
Unknown Burden
An elemental pool, bubbling over with acid.

You examine the elemental pool, being careful not to get too close.

You give Acidic Elemental Pool <Weeping Weapon>.
<Character Name> submerges the Weeping weapon in the acidic pool. The weapon takes on the elemental power of Acid!