Is it possible to charge a paper with coming light from sliding slit lens and coat the exposed paper area with graphite powder and finish with sandwiching with a plastic foil ? I think this is one of a e paper solution and there is no chemical to dirt the nature , material is abundant .
Best ,
Mustafa Umut Sarac
Istanbul
Try googling ESDA for some ideas (ESDA=ESDA stands for Electrostatic Detection Apparatus. It is used to detect and to assist in the decipherment of indented impressions of handwriting on paper.)
Photocopiers use an electrostatic drum to form the image then transfer it to the paper.
Transparent Titanium Dioxide? If you can get some samples from a supplier of sunscreen raw materials this would prove a point. BASF (Z-Cote), Croda/Uniqema(Tioviel), Mitsubishi, Merck (Eusolex-T-AVO) and others make them. Be aware that there are two different crystal types of titanium dioxide. (Rutile and Anatase)One is photocatalytic, the other inert. This was found out when in the 50's white lead was beginning to be replaced with Ti02. Using the wrong crystal type makes the paint fall apart in sunlight.
This sort of question might get a better response on the Hybridphoto.com website