Ember required for weapon ascension.
The church long hid the forbidden black ember,
and no living blacksmith knows of it.
Ascends +5 divine weapon to occult weapon.
(occult weapons can be reinforced to +5)
Occult weapons were used to hunt the gods,
and are effective against their following and kin.
Found in the Painted World of Ariamis
It is inside the Annex, so it will require the Annex key to enter. It is located in the courtyard, but after you pick it up several Crow Demons will ambush you - video