3.1.2. White

High pixel intensities in the titanium MA-XRF map suggest the use of titanium white in white regions of plate 55, such as the white flower (Figure 3) [33,37]. Titanium white was not commonly available as an artist's pigment before around 1920, thus moving the *terminus post quem* for the coloring on plate 55 to the first quarter of the twentieth century [33]. Characteristic features in reflectance data for titanium white fall between 393 and 406 nm, which is outside the range of the hyperspectral camera used for this study [38,39]. Therefore in our case HSI is not useful in confirming this identification.

**Figure 3.** Visible light photograph and (**left**) and MA-XRF map for titanium in Plate 55 (**right**).

High pixel brightness in XRF maps for zinc, barium and sulphur occurred in several regions of all three prints (Figure 4). This combination is consistent with the use of lithopone, which consists of zinc sulfide and barium sulphate [32,40]. Lithopone is a white pigment, but is observed here in regions that visually appear green and blue, suggesting its use as a filler. Lithopone was first patented and commercially produced in 1878; thus, its presence on these prints further confirms that the coloring on the prints is modern [32]. The use of two whites may suggest the use of two campaigns of coloring, or the choice to differentiate areas of the print.

**Figure 4.** False color images indicating brightness in the XRF maps for Ba\_L, S\_K, and Zn\_k in plates 9 (**left**) 54 (**center**) and plate 55 (**right**).

#### 3.1.3. Red

High pixel brightness in cadmium, sulphur, and selenium XRF maps in several red regions of plates 54 and 55 (Figure 5) suggests the use of cadmium red to color red regions in both prints [30,41]. Characteristic spectra in hyperspectral data Figure 6) are consistent with those for cadmium red [30,41] namely the inflection point around 590 nm and absorption maximum around 500 nm. Cadmium red became commercially available in 1919, confirming the early twentieth century *terminus post quem* for the coloring [30].

**Figure 5.** False color images indicating brightness in the XRF maps for Cd\_L, S\_K, and Se\_K, in plates 54 (**left**) and plate 55 (**right**).

**Figure 6.** Characteristic spectra for unidentified green (**left**) and cadmium and barium-rich reds (**right**).

Additionally, we observe that in the upper left-most pepper of plate 55 and in the uppermost spike of the flower on plate 54, circled in red in Figure 7, pixel intensities in cadmium XRF maps are a factor of 4 lower than the pixel intensities in other red regions of the cadmium map of the same print. The pixel brightness for selenium is also low in these areas and barium remains constant throughout. Because visibly the red remains consistent, it is possible that in these regions a second red, possibly an organic red with a barium-rich substrate, such as barium oxide, was applied in addition to cadmium red [31].

Pixel brightness is low in all regions of the Selenium XRF map for Plate 9 (Figure 8), indicating that cadmium red was not used in Plate 9. Cadmium and barium are found together in red regions of plate 9 (Figure 7), suggesting the use of cadmium barium red [30,42] in plate 9 or possibly, as in plates 54 and 55, a barium-rich organic red. The presence of multiple reds could indicate multiple distinct campaigns of coloring or the choice to distinguish or retouch parts of the prints. The shared use of cadmium red between plates 54 and 55 suggests that both were produced using a shared palette.

**Figure 7.** Details from plate 55 (**left**), plate 9 (**center**), and plate 54 (**right**) showing XRF maps for barium and cadium.

**Figure 8.** Visible light photograph and (**left**) and MA-XRF map for selenium in plate 9 (**right**).
