Removing old over paint
Old restoration can discolour and deteriorate. The example on the right shows the remains of the blue overpaint in the process of being removed. This was liberally applied over the whole sky, covering details of original paint that were in good condition. The result of the conservation treatment to this 17th Century panel painting was to reveal the painting as per the artists original intention, without the 19th Century intervention.
Image right shows remains of blue overpaint during overpaint removal.