## 3 Results  
### Vis-NIR Multispectral Reflectography  
Enhanced instrumental resolution was ensured by raster acquisition performed with oversampling (4x) in both x and y scanning directions, while proper image deconvolution was applied to the datacube. False-color imaging, which was performed on the high-resolution images following the processing described above, revealed traces of the preliminary drawing that outlines the steep cliff on the left of the waterfall and the fortress on the promontory. Details of the rocky wall can be observed in Figure 2, which displays the FC images obtained by combining the NIR -at 1292 nm, the red, and the green images (Figure 2b,d), and PC2, PC3, and PC4 images (Figure 2c,e). According to XRF analysis of the same areas [27], the sketch was drawn with a lead stylus, which is consistent with findings pertaining to other drawings by the same author. The use of a lead stylus is particularly evident in the reported NRG-FC images, where a dark line is visible beneath the red of the main drawing. The same lines appear bright orange in the PC-FC images. [PERSON] used to draw with different metal points: lead, which is soft and easy to erase, was used to sketch out drawings that were then refined with a pen; silver and metal alloys were preferred for figure sketches and studies, often completed with lead white highlights [30]. The preliminary sketch in metal point was completed with another tool, possibly a dip pen, in two successive steps [31]. Multispectral analyses showed the presence of two distinct drawings, one outlining the main composition with pale brown lines and the other defining more intense-colored details. The different spectral behavior of the two materials is especially evident in the NIR image at 1600 nm (Figure 3a), where all the main elements of the landscape become transparent except for the outline of the rocks, the fine strokes defining the vegetation in the foreground, and the maelstrom at the bottom of the waterfall. XRF identified common chemical elements in the two types of ink distribution, namely iron, copper, and sulphur. This is consistent with iron-gall ink, and, more specifically, with hydrated green and blue vitriol (FeSO4-nH2O and CuSO4-nH2O, respectively), which were typically added to tann acid solutions to obtain ink [27; 32]. The different absorption properties of the two drawings suggest that [PERSON] may have used a more diluted, and therefore IR transparent, ink for the main composition, and a more concentrated one for defining specific details [27]. Reflectance spectra (Figure 3d) acquired in the three points shown in Figure 3c confirm the similarities between the two ink compositions. The marked rising in reflectance beyond the red region (inflection point occurring at ca. 730 nm), which accounts for the brownish tone perceived in the visible, is compatible with metal-gall inks [33]. In the analyzed drawing, the overall degree of reflectance appears lower as the ink's hue becomes darker, with a rise occurring in the NIR. Conversely, the lower hiding power of the more diluted iron-gall ink mixture inevitably determines a higher contribution of the paper support, which, in its turn, affects the position of the inflection point in the resulting reflectance spectrum [34]. While there are studies relating the ink's hue to its metal content [35], such a hypothesis requires further verification, especially when considering that artists would often add organic carbon to the mixture to enhance its dark tone. Moreover, recipes for iron-gall inks are numerous and varied, and may include very diverse components and impurities, each undergoing various degradation processes resulting in color changes. In our case, browning and darkening may have resulted from  
Figure 2: Traditional false-color and trichromatic RGB PC processing reveals the presence of the underdrawing in lead stylus on the recto. (**a**) White dashed rectangles on the RGB image indicate the regions where the preliminary sketch was observed.