Daguerreotypes – The Science of Early Photography

In 1839, a new photography technique was introduced: the daguerreotype, named after its inventor Louis Jacques Mandé Daguerre. It consisted of a silver-plated metal sheet that was sensitized by iodine fumes to generate a photosensitive silver iodide cover on its surface. When this sheet was exposed to light in a camera, a latent image was created. After the development and fixing process, the final daguerreotype image was obtained.

The daguerreotype was a major development for photography. At the beginning of the 1840s, further progress was achieved by photography specialists in Vienna, such as lenses that reduced exposure times, improved photosensitivity by new sensitization methods using combinations of iodine, bromine, and chlorine, and new development procedures which made it unnecessary to use harmful mercury vapors. In addition, in 1840, the Austrian anatomy professor Joseph von Berres produced printing plates for the first reproduction of photographs by etching daguerreotype plates. This etching technique is still widely unexplored.

Valentina Ljubić Tobisch and Wolfgang Kautek, University of Vienna, Austria, have conducted a detailed material analysis of a newly discovered daguerreotype from the 1840s provided by the Vienna Technical Museum. The plate was probably etched by Berres. The team used both historical literature and analytic techniques to unveil the relevant chemical steps in the photographic procedure. They used surface measurements such as scanning secondary electron microscopy (resulting images pictured) and profilometry studies with an optical microscope, as well as material analysis via electron dispersive x-ray (EDX) spectroscopy.

Surface analysis showed that the photographic process involved the formation of colloidal Ag nanoparticles with sizes of 30–120 nm in the light-exposed areas of the plate (pictured left). The investigated plate exhibits etched areas. Berres applied a gum arabic solution on the fixed image surface before the etching step. The gum arabic preferentially wetted the exposed Ag nanoparticle regions, so that unexposed areas could be etched using HNO₃. The formed depressions could then accept printing ink in the following reproduction step. The results of this work could help with subsequent studies of early prints and photography.