It is not clear whether Ruskin has in mind any particular painting by Leonardo da Vinci as an example of Leonardo's finish in walls. The Adoration of the Magi mentioned at MP I:85 is a possibility (and there are also studies for it, including its walls, in the Louvre and in the Uffizi); another possibility would be the Annunciation in the Uffizi, mentioned at Works, 23.325; a painting which has sometimes been attributed to Ghirlandaio, though Ruskin is convinced that it is Leonardo's work.