The Coated Salted Paper Prints from the Eduard Isaac Asser Collection at the Rijksmuseum: FTIR and OCT Identification and Characterization

The Rijksmuseum holds four valuable albums with 187 photographs made by Eduard Isaac Asser (1809–1894), one of the first figures in photography in the Netherlands. Based on visual examination, most of these prints have been identified as salted paper prints with a coating, but they can be hard to distinguish from matte or glossy albumen prints, especially where the coating is thick. In order to be more accurate in our descriptions and to better understand Asser’s technique, a technical study of his work was conducted. Fourier transform infrared spectroscopy (FTIR) helped us to identify, to a certain extent, the nature of the coatings. Before the analysis, the prints had been described either as “shellac coated” or as “waxed,” based on their varying degree of sheen. FTIR identified a larger number of substances in the coatings: gum, protein, natural resin, and possibly starch. Optical coherence tomography (OCT) was also used to study the coatings. Because OCT has limitations when dealing with very thin layers, it was not always suitable for distinguishing coated salted paper prints from coated albumen prints. However, it did turn out to be a useful tool to explore the topography and structure of the paper supports and the coatings.