When the children of our people came of age, they earn the privilege of wearing the vallaslin, the blood writing. It sets us apart from the shemlen, and from the elves who have thrown their lot in with them. It reminds us that we will never again surrender our traditions and beliefs. —From Codex entry: Vallaslin: Blood Writing
Blood writing, or vallaslin in the elven language, is what the Dalish call the intricate facial tattoos worn by all adult clan members. When a Dalish elf comes of age, they prepare to gain the vallaslin by meditating on the gods and the ways of the Dalish, and by purifying the body and the skin. When the time comes, the Keeper of the clan applies the blood writing. This is done in complete silence. Cries of pain are taken as signs of weakness. If a young elf cannot tolerate the pain of the blood writing, they are deemed unready to undertake the responsibilities of an adult. The keeper may stop the ritual if they decide that the one gaining the vallaslin is not ready. Blood writing is at least in part a religious practice, and there are different designs of blood writing representing deities in the Elven Pantheon. However, it is not known whether the practice was associated with the worship of the gods in ancient Elvhenan or is a more recent development.
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According to Solas, vallaslin is a much more controversial concept than believed by modern elves -- the Dalish in particular. He reveals that the tattoos are not signs of patronage to the various elven gods but, in fact, slave markings--signs of ownership--dating from the time of Elvhenan, when noble elves enslaved the lower classes; they are representations of the gods that the nobles favored. Abelas and the Sentinels of the Temple of Mythal had vallaslin etched on their faces.
Thus far, two groups of Dalish have been encountered: those of the Dalish Elf Origin and those of Zathrian's clan in Nature of the Beast. Various designs of blood writing can be seen on their faces, but it is not known which design is associated with which deity. There appear to be eight main designs, each of which comes in a simpler and a more complex version. Though similar to the main eight there are two unique designs that are used by Velanna/Seranni in Dragon Age: Origins - Awakening and Merrill in Dragon Age II.