The Cultist's Ritual Tome is a common book found on dead cultists. It explains the requirements needed to execute the ancient skull's purification ritual.
Curse Removal Instructions
The removal of curses are permitted only of elders of the brotherhood. It is only they who should be entrusted with the white staff.
The Ritual Site
The location that the ritual is performed must meet the following specifications. A circular stone altar at the center of the intended ritual site must have a flat surface on top that is approximately a person's length in diameter. Surrounding the center piece must stand five squared-off stone pillars equidistant from each other. On top of each pillar there is to be a place to build a fire.
Performing the Ritual
Upon nightfall, place the cursed object on the center of the altar and slowly move the tip of the white staff near the object. This will begin the cleansing ritual. It is important that you keep the tip of the staff close to the object during the ceremony as it will expel the curse from the object. The cleansing can take some time. Some of the most powerful curses have senses of self-preservation, so be extra cautious when dealing with objects of that class.
If at any time during the ritual the cursed object displays signs of extreme anger, temporarily remove yourself from the immediate proximity of said object until its anger either erupts or dies down.