Unfortunately we don’t have a mural specialist here at the National Museum (as of December 2020), so I recommend that you make contact with the conservators at NIKU (the Norwegian Institute for Cultural Heritage Research). Once paint has faded due to exposure to direct sunlight, it’s unfortunately impossible to reverse the fading or prevent further fading. Flakes of paint can be glued back into place; you should do this using a special-purpose glue. The conservators at NIKU will be able to advise you about this.

Kind regards from Laura, paintings conservator