*3.5. Polychromy Analysis*

#### 3.5.1. Original Polychromy

The polychromy was done following the European artistic tradition. Over the final layer of maize stem paste, the artist applied a preparation layer made of *gesso grosso*, containing mainly anhydrite (CaSO4), identified thanks to the 1095 cm−<sup>1</sup> band from the νS=O in the μ-FTIR spectra (Figure 6f). Anhydrite, obtained by roasting gypsum, was traditionally used for ground layers in Southern Europe until the 16th century [50]. A particular characteristic of the ground layer of this sculpture is the presence of a cellulosic material (probably maize stem fragments) used as a filler (Figure 6a,d). These fragments are present in the different cross-section samples. The weak bands at 1656 cm−<sup>1</sup> and 1548 cm−<sup>1</sup> (data not showed) arising from ν(C=O) and NH, respectively [50], suggest the used of animal glue as a binder for the ground layer.

**Figure 6.** (**a**) SSE-1 cross-section, 20x; (**b**) Map of the band 1095 cm−<sup>1</sup> from the SO4 <sup>2</sup>−; (**c**) Map of the band at 3526 cm−<sup>1</sup> from OH of gypsum; (**d**) Map obtained integrating the area of the band at 1029 cm−<sup>1</sup> from the νCO at C6 [51] of cellulosic material used as filler; (**e**) Map of the band at 1735 cm−<sup>1</sup> from the C=O of the oil binder; (**f**) FTIR spectra from layers 0 (anhydrite) and 3 (gypsum) of sample SSE-1. The inset shows the bands attributed to animal glue as a binder; (**g**) FTIR spectrum obtained from layer 1, the bands associated with the binder marked with \*; (**h**) FTIR spectrum of the dark red layer (layer 2) where the band at 1409 cm−<sup>1</sup> indicates the addition of lead white and the band at 1099 cm−<sup>1</sup> suggests the presence of sulfates (probably calcium sulfate).

The cross-section analysis suggested that the original loincloth decoration was simple as the artist used the white color of the ground layer. Additionally, we identified the remains of the painted blood in the samples SSE-1 and SSE-2. The SEM-EDX (Table 2) and μ-Raman (Figure 7b) results suggested that the artist used two different red pigments applied in two layers; the first one contains vermilion (HgS), which has an intense red color, while the second was made using a red lake, most probably a cochineal lake, to achieve a darker hue to represent coagulated blood. The SEM-EDX results (Table 2) indicated the presence of Al, K, and Si in the dark red layer, probably associated with the lake substrate (alum [KAl(SO4)2·12H2O]) and traces of Cu, previously related to the use of insects for the lake preparation [52]. Lead white was also added to the mixture, as suggested by the SEM-EDX (Table 2) and μ-FTIR results (Figure 6g,h), probably as a drier [53].



**Figure 7.** (**a**) SSE-1 cross-section, 20×; (**b**) Raman spectrum of the red layer (layer 1) of sample SSE-1, compared to that of cinnabar; (**c**) Raman spectrum obtained from the upper white layer (layer 3) of SSE-1 compared to the spectra of anhydrite and gypsum; (**d**) SEE-2 cross-section, polarized light, 50×; (**e**) Raman spectrum of the original flesh-tones (layer 1) compared to that of cerussite.

The original flesh-tones were rendered using lead pigments, as suggested by the SEM-EDX results (Table 2) of sample SSE-2. In the μ-Rama spectrum (Figure 7e), the band at 1053 cm<sup>−</sup>1, arising from the ν1(a'1) CO3 <sup>2</sup>−, suggested the presence of lead white [54], mainly constitute by cerussite (PbCO3), which indicates an "inversed" proportion between cerussite (generally the minor component in the mixture) and hydrocerussite (2 Pb3(CO3)2(OH)2) produced by acidic processing of lead white pigment by washing or grinding with vinegar as suggested by Gonzalez [55].

The μ-FTIR analysis of sample SSE-1 (Figure 6e,g,h) suggests that the artist used a drying oil as a binder due to the band at 1735 cm−<sup>1</sup> from the ν(C=O) of the esters of the oil. Additionally, the spectra showed the characteristic bands of degradation products from the binder, such as free fatty acids (suggested by the band at 1710 cm−<sup>1</sup> [56]) and Pb carboxylates (associated with the band at 1517 cm−<sup>1</sup> and a shoulder at 1539 cm−<sup>1</sup> [56,57]).
