Separation Science Group, Department of Organic and Macromolecular Chemistry, Faculty of Sciences, Ghent University, Krijgslaan 281 S4 Bis, B-9000 Ghent, Belgium; Paintings Lab, Laboratories Department, Royal Institute for Cultural Heritage (KIK-IRPA), Jubelpark 1, B-1000 Brussels, Belgium; Conservation and Restoration of Cultural Heritage, Amsterdam School for Heritage, Memory and Material Culture (AHM), Faculty of Humanities, University of Amsterdam, P.O. Box 94552, 1090 GN Amsterdam, the Netherlands. Electronic address: jonas.veenhoven@ugent.be.