Pentimento

A pentimento (plural pentimenti) is an alteration in a painting, evidenced by traces of previous work, showing that the artist has changed his or her mind as to the composition during the process of painting. The word is Italian for repentance, from the verb pentirsi, meaning to repent.
See also Palimpsest.
More information on the Wikipedia page which includes examples and links. There is various other coverage on the web and in print, eg .
Category:Reference