Highly Photosensitive Daguerreotypes and their Reproduction: Physico‐chemical Elucidation of Innovative Processes in Photography Developed around 1840 in Vienna

A physico‐chemical elucidation of the first photographic technology that allowed manifold reproduction is presented. An etched daguerreotype manufactured around 1840 in Vienna, preserved by the Technisches Museum Wien, served as a case study. Surface analysis showed that the photographic process involved the formation of colloidal Ag nanoparticles with sizes of 30–120 nm with shell layers consisting of Ag 2 O, Ag 2 S, and some AgCl. This breakthrough photographic technique provided a hitherto unachieved high sensitivity because of various halogenide mixtures without the use of Hg. The image development consisted of the reduction of the Ag halides by H 2 SO 3 created by the hydrolysis of S 2 Cl 2 leading to the formation of Ag nanoparticles adjacent to the Ag nuclei of the latent image. The fixing of the image was performed either by KCN or by Na 2 S 2 O 3 . The investigated plate exhibits etched areas with Ag 2 O conversion layers and no Cl or S. The gum arabic use for etching preferentially wetted the exposed Ag nanoparticle regions so that unexposed areas could be etched by HNO 3 .