Why does the exposure route matter, and what's the risk? 

With the rise of nanotechnology, research in recent years has also shown the dangers of titanium dioxide (TiO2) nanoparticles, and their genotoxicity, which refers to a chemical agent’s ability to harm or damage DNA in cells, thus potentially causing cancer. 

The author thanks Marco Leona, Scientist-in-Charge of the Department of Scientific Research at the Metropolitan Museum of Art for conducting fluorescence spectrometry on Wheel of Fortune and a valuable discussion of the research, as well as Silvia Centeno, Research Scientist at the Metropolitan Museum of Art, who performed Raman analysis on the watercolors and also contributed her insight. The phenomenon of the phosphorescing lithopone was originally discovered during the author's fellowship in the Sherman Fairchild Center for the Conservation of Works on Paper, funded by the Andrew W. Mellon Foundation. The author thanks all her colleagues for their ideas and support during the research of this paper, and special thanks to Rachel Mustalish for her assistance in editing this work.