Darkening of Historic Paintings

de bene esse: literally, of well-being, morally acceptable but subject to future validation or exception

Why are reds in paintings getting darker over the centuries?

http://www.medievalists.net/2013/12/03/casting-light-on-the-darkening-of-colors-in-historical-paintings/

Casting Light on the Darkening of Colors in Historical Paintings - Medievalists.net

medievalists.net

Many archeological sites, cathedral wall paintings, and famous masterpieces from major painters are affected by a slow, irreversible, light-induced degradation of pigments