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 Ag2 O, Ag2 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 H2 SO3 created by the hydrolysis of S2 Cl2 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 Na2 S2 O3 . The investigated plate exhibits etched areas with Ag2 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 HNO3 .
Keywords: daguerreotypes; heritage science; nanoparticles; photochemistry; photography.
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.