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.

Johannes Vermeer (1632–1675) is known for his brilliant blue colours, and his frequent use of the costly natural ultramarine. This paper reveals new findings about ultramarine in the headscarf of Girl with a Pearl Earring (c. 1665, Mauritshuis). The painting was examined using a range of micro- and macroscale techniques as part of the Girl in the Spotlight research project (2018). Analysis of micro-samples mounted as cross-sections using SEM–EDX and FTIR-ATR showed that Vermeer used high-quality ultramarine in the blue headscarf, based on the relative abundance of bright blue particles of lazurite. Analysis with synchrotron sulphur K-edge XANES suggested that the ultramarine pigment was prepared—at least in part—from a heat-treated lapis lazuli rock. The entire painting was imaged using MS-IRR, MA-XRF, RIS, and digital microscopy to reveal the distribution of materials of the headscarf, and to give more insight into Vermeer’s painting process. The shadow part of the headscarf has a remarkably patchy appearance, due to paint degradation that is probably related to the large amounts of chalk Vermeer mixed in the ultramarine paint in this area. The question was raised as to whether extra chalk was added deliberately to the paint to adjust the handling properties or opacity, or whether the chalk was the substrate of a—now faded—yellow lake. Schematic paint reconstructions were made to investigate the effect of the addition of chalk or yellow lake on the paint properties. The analyses and reconstructions led to the hypothesis that the blue headscarf originally contained a wider range of different blue colour shades: an opaque light blue for the left (lit) zone, a slightly brighter opaque blue for the middle zone, and a deep dark blue-green glaze with alternating blue-green glazing brushstrokes for the shadow zone—now largely compromised by paint degradation.