Your avatar's face became covered with soot, and it remained for the entire day.
A Sootface will revert to its previous condition after saving changes to the avatar, but some users liked the look and decided to keep it.
This status was intended to be temporary, and therefore CANNOT be recovered after it is gone.
...See also Invisibob, as they are directly related to the Sootface.
I love my Sootface!