Xiahou Dun's Eye Patch and Glass Eye

Origins
Xiahou Dun was a military general serving under the warlord Cao Cao in the late Han Dynasty. In a battle against  Lu Bu in the late 190s he lost his left eye when it was struck by a stray arrow. For the remainder of his life he was known as "Blind Xiahou", a name he greatly despised. A glass eye was fashioned for him, though he frequently wore an eye patch dueto his disgust at his disfigurement.

Effects
The wearer of the eye patch sees not black, but whatever the glass eye is pointing at. Because of this, when the eye patch is worn over the glass eye the user sees incomprehensible colours and shapes, mentioned by Warehouse 6 agents as "glimpsing a heavenly realm beyond our understanding". Modern agents suspect this to be the reason for Xiahou's anger and refusal to use the eye.

Warehouse 13
The glass eye was lost in 1919 during the movement of artifacts from Warehouse 12. It went missing in the Madrid Sector and has not been found since. The eye patch rests on a shelf in Artie's office and during downtimes agents sometimes use it to (unsuccessfuly) find the eye.