The History and Chemistry of Platinum-toned Salted Paper Prints

ABSTRACT A wealth of period literature from as early as 1856 through the 1920s promoted the toning of salted paper prints with platinum to achieve certain aesthetic effects and improve silver image permanence. A variety of toning bath compositions were proposed to achieve a range of image tones. Additionally, other platinum and matte silver photographic processes, such as kallitypes, silver-platinum prints (e.g., “Satista”), and silver-intensified platinum prints, were popular during the salted paper print revival and may have similar characteristics. However, few examples of prints containing both silver and platinum have been identified in museum collections. To investigate their chemical natures and range of appearances, the authors fabricated prints according to historic recipes. These simulacra were analyzed by XRF spectroscopy and color measurement and artificially aged to provide data relating to metal content, appearance, and longevity. High-resolution electron microscopy of the salted paper print samples revealed the chemical influence of the toning method on the metallic nanostructures that comprise the image. Ultimately, the analytical results are tied to visual observations to elucidate toning methods used by early photographers, contribute to process identification, and draw conclusions about the conservation of these materials.