Characterization of unprocessed historic platinum photographic papers by Raman, FTIR and XRF

Five unprocessed historic platinum photographic papers were characterized by a combination of Raman, FTIR and XRF spectroscopies to gain insight into their manufacturing processes and obtain information that can help identify the use of similar papers in works of art in a non-invasive manner. The analysis of one of these papers, 'Japine Platinotype for Sepia Tones,' showed a sensitized surface layer in the recto consistent with the use of a parchmentization process of the paper substrate, and that the verso presents a slightly modified surface. Raman and FTIR measurements revealed that this surface layer in Japine is composed mainly of amorphous cellulose. No gelatin or other surface coatings were found to be present in Japine. In the rest of the papers studied, the sensitizer was found to have been applied directly onto the paper fibers and no gelatin or gums were observed as sizings. Relatively larger amounts of mercury were detected in Japine, confirming the use of a Hg salt in a sepia-type platinum paper. The combined use of Raman and XRF provides information that can help discriminate platinum photographic processes involving parchmentization in works of art in a non-invasive manner.