Bruno Eckhardt, Jakub S. Prauzner-Bechcicki, Krzysztof Sacha, and Jakub Zakrzewski Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg, Germany 2 Faculty of Conservation and Restoration of Works of Art Academy of Fine Arts, Smoleńsk 9, Kraków, Poland Marian Smoluchowski Institute of Physics and Mark Kac Complex Systems Research Centre, Jagiellonian University, Reymonta 4, 30-059 K...