The White Chrism is a secret item introduced in Silent Hill 2.
The White Chrism is a blessed item of the Order, necessary for many rituals including the Ritual of the Holy Assumption and Rebirth ritual. It is a thin bottle containing white oil, with a label reading "I deny thee".
Silent Hill 2: Born from a Wish
The White Chrism is referenced in the Born from a Wish scenario. The chrism is represented by a white board. Maria must collect the white board (along with three other boards representing the three other items) in order to solve the Acacia Key Puzzle.
The White Chrism is physically picked up by Maria upon the request of Ernest Baldwin. Like in the larger scenario, it is located in the Blue Creek Apartments inside Room 105. However, the name has been changed to "White Liquid" rather than White Chrism.
Silent Hill 2: Letter from Silent Heaven
It is found on a counter in Room 105 on the first floor of the Blue Creek Apartments in Silent Hill 2, and is required for the "Rebirth" ending. It can only be unlocked after completing the game once.
Silent Hill 4: The Room
Henry Townshend also sees the oil on a table along with the Obsidian Goblet when he opens the secret room with Walter Sullivan's corpse. It indicates that the white liquid substance is used by Walter to commence the Ritual of the Holy Assumption and live on as a Ghost.
Silent Hill: Book of Memories