## 3 Results
### The Polychromy Scheme
The diffuse red color on the hair of the sphinx was characterized by a different XRF spectrum which included intense X-ray lines of Fe, accompanied by less intense lines of Mn, elements that are associated with red-brown ochres. Figure 3: Imaging of the proper right wing of the sphinx: (**A**) VIS image showing traces of the original colors of the feathers; (**B**) VIL image illustrating the presence and distribution of the luminescence of Egyptian blue between the feathers; (**C**) IRR image highlighting the presence of black outlines defining the feathers, indicated by the red arrow. The detection of well-resolved, intense X-ray energy lines of Hg, associated with weak lines of S, by pXRF on darkened areas revealed the consistent presence of mercury sulfide, most likely a combination of cinnabar and metacinnabar (\(\beta\)-HgS) [32; 33; 34; 35; 36; 37]. An XRF line scan recorded across the proper left eye showed variation in intensities of Hg and Fe X-ray lines, suggesting that cinnabar was used either in purity or mixed with ochre to represent the iris, and possibly the pupil (Supplementary Materials: Figure S5). An Fe-based pigment containing traces of Mn, likely a red ochre, was also identified on the inscribed letters of the base and the shaft background, the youth's eye and hair, the sphinx's hair, carpal pad ([PERSON]'s pisiform bone), and in the areas between the wings and the tail's curl by pXRF analysis. In other locations, such as the sphinx's face, the leonine body, and the wings, the Fe-based pigments were either hindered by a thick crust resulting from burial or so scarce that their identification was not possible by means of non-invasive techniques. Digital microscopy proved essential in locating Fe-based pigment particles in highly disturbed surfaces, such as the sphinx's lips (Supplementary Materials: Figure S4C), where residual traces of the pigment were found deep in the groove that defines the lips. First observations by digital microscopy suggested that all the pigments were applied directly to the marble substrate. Based on the combination of multiband imaging and XRF analysis, two types of Cu-based blue pigments were identified, as well as at least two types of red pigments, Fe- and Hg-containing, respectively. The presence of yellow, black, and white pigments was also inferred from observation of the surface at high magnifications. In an attempt to define the original color scheme and inform reconstruction of the sphinx, elemental maps were collected by sXRF on selected areas of the sphinx's diadem, wing, and chest, and the capital (Figure 4). Figure 4: Locations of XRF maps and micro-samples. The arrows indicate sampling locations that are not visible in this frontal image. Although currently completely concealed by a thick crust, glimpses of the original decoration of the diadem could be seen by shining a strong light through the marble (Supplementary Materials: Figure S6). Scanning XRF in this area helped identify the chromatic scheme of the decoration, by associating characteristic elements with specific pigments. The distribution of Hg, Cu, and Fe on the analyzed area of the diadem (Figure 4, area B, and Figure 5) reproduces the geometric design; in particular, Hg and Cu clearly identify the design of repeating red and blue meanders. The presence of Hg is indicative of cinnabar, whereas Cu suggests the use of a Cu-based pigment, possibly azurite, as the absence of luminescence in VIL images excludes the presence of Egyptian blue. Although the distribution of Fe might be indicative of the presence of Fe-containing pigments, mostly ochres, its identification is complicated by the abundance of iron oxides/hydroxides in accretions and patinas. Two areas of the proper right wing (Figure 4, areas A and E) were also scanned with sXRF to reconstruct the design and color scheme of the feathers, even where minimal residues of the original pigments were observed.