19th March 2014, 10:26 PM
Marc Berger Wrote:How does it work if you had to clean the picture but it was face down on the floor.
I would pick the picture up and turn it so its painted face was up. If you were to remove deposits from the back of the painting then this represents a different face and the deposits on this face do not have any direct stratigraphic relationship with the paint on the other side.
let's say the face down painting is instead a collapsed painted ceiling. The collapse of the ceiling transforms it into a new layer which is later than the surface it fell onto even if the painting and ceiling were originally earlier than the lower layer.