*3.4. Orange*

In orange areas, the most evident and common feature of the three walls is the disappearance of Sb from the XRF analysis with respect to the corresponding yellow areas (Tables 2 and 3). In Alexander's mantle on the north wall, the use of red ochre added to the yellow ochre was identified. In addition, the presence of Pb was seen by XRF, and the first derivative of reflectance with the hinted maximum at 510 nm (Figure 9, line 1) also suggests, if compared with other litharge-based areas (Figure 9, lines 2, 4), its presence, which is not so strange due to its yellow/orange hue (Figure 9, area 1).

**Figure 8.** Comparison of first derivative reflectance spectra, recorded on selected yellow areas (lines 1–4).

calcium carbonate.

simultaneous presence of Pb and Sb.

**Figure 7.** Raman spectrum of Roxane's yellow dress showing the presence of lead antimonate and

The presence of Naples yellow is also found on the third wall, as revealed by XRF and Raman spectroscopy (Table 3). However, in these areas, the first derivative of reflectance spectra almost exclusively shows the shape of litharge (Figure 8, lines 3, 4), as can be seen from Figure 8 by comparison with the reflectance spectrum on the landscape of the north wall (mostly litharge and yellow ochre, Figure 8, line 2) and with the dress of Roxane's maid, which in reflectance shows mostly yellow ochre (Figure 8, line 1). The striking presence of litharge allows for its otherwise difficult identification, due to the

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**Figure 8. Figure 8.** Comparison of first derivative reflectance spectr Comparison of first derivative reflectance spectra, recorded on selected yellow areas (lines 1–4). a, recorded on selected yellow areas (lines 1–4). ened maximum at 510 nm compared to their yellow counterparts (Figure 9, lines 2, 3 and lines 4, 5).

**Figure 9.** Comparison of first derivative reflectance spectra, recorded on selected orange and yellow areas (lines 1–5). **Figure 9.** Comparison of first derivative reflectance spectra, recorded on selected orange and yellow areas (lines 1–5).

*3.5. Blue*  The blue areas in each of the three walls studied are characterized by the presence of Co, which corresponds—in most cases—to the reflectance spectrum of smalt. Along with Co, associated impurities such as As and Bi are always found. On the east wall, smalt is used to create the shades in the white robe of one of Darius' daughters (Figure 10, area 1) and in the white cloak of Hephaestion (Figure 10, area 2). It Additionally, on the third wall, the orange areas are characterized by mixtures of yellow and red ochre, with the presence of Pb seen from XRF (Table 3). The use of litharge is also perceivable in the orange hue of the dress of both young Alexander and his father Philip II of Macedon, when considering in the first derivative of their reflectance the weakened maximum at 510 nm compared to their yellow counterparts (Figure 9, lines 2, 3 and lines 4, 5).

### is also found mixed with hematite to obtain the gray/purple hue of Sisigambi's dress, as *3.5. Blue*

already highlighted above (Figure 5, area 3). On the third wall, the use of smalt returns, as indicated by the presence of Co, Bi, and As, in the dark blue areas of Alexander's father's robe, Philip II of Macedon (Figure 10, area 4), and in the white garment of the young The blue areas in each of the three walls studied are characterized by the presence of Co, which corresponds—in most cases—to the reflectance spectrum of smalt. Along with Co, associated impurities such as As and Bi are always found.

Alexander taming the horse Bucephalus (Figure 10, area 3). The first derivative of the reflectance spectra measured in the same points confirms its presence (Figure 10). On the east wall, smalt is used to create the shades in the white robe of one of Darius' daughters (Figure 10, area 1) and in the white cloak of Hephaestion (Figure 10, area 2). It

is also found mixed with hematite to obtain the gray/purple hue of Sisigambi's dress, as already highlighted above (Figure 5, area 3). On the third wall, the use of smalt returns, as indicated by the presence of Co, Bi, and As, in the dark blue areas of Alexander's father's robe, Philip II of Macedon (Figure 10, area 4), and in the white garment of the young Alexander taming the horse Bucephalus (Figure 10, area 3). The first derivative of the reflectance spectra measured in the same points confirms its presence (Figure 10). *Heritage* **2021**, *4* FOR PEER REVIEW 13

**Figure 10.** Comparison of first derivative reflectance spectra recorded on selected blue areas (lines 1–4). **Figure 10.** Comparison of first derivative reflectance spectra recorded on selected blue areas (lines 1–4).

On the north wall, two different blue pigments were individuated: smalt and lapis lazuli, with the latter univocally identified by infrared spectroscopy (Figure 11) thanks to its characteristic infrared band at 2340 cm−1 [20]. Both these pigments have been used to obtain different shades of blue in different ways, namely: On the north wall, two different blue pigments were individuated: smalt and lapis lazuli, with the latter univocally identified by infrared spectroscopy (Figure 11) thanks to its characteristic infrared band at 2340 cm−<sup>1</sup> [20]. Both these pigments have been used to obtain different shades of blue in different ways, namely:


**Figure 11.** Infrared reflectance spectrum recorded on putto's dress, north wall. The lapis lazuli characteristic infrared band is evidenced in the spectrum. **Figure 11.** Infrared reflectance spectrum recorded on putto's dress, north wall. The lapis lazuli characteristic infrared band is evidenced in the spectrum. **Figure 11.** Infrared reflectance spectrum recorded on putto's dress, north wall. The lapis lazuli characteristic infrared band is evidenced in the spectrum.

**Figure 12.** Comparison of first derivative spectra of visible reflectance spectra recorded on selected blue areas (lines 1–4). **Figure 12.** Comparison of first derivative spectra of visible reflectance spectra recorded on selected blue areas (lines 1–4). **Figure 12.** Comparison of first derivative spectra of visible reflectance spectra recorded on selected blue areas (lines 1–4).

Further lapis lazuli finishes would also seem by now lost or seriously compromised, as can be seen from the heavy repainting of some mantles, to restore the outlines that are no longer perceptible, including Alexander's dress, which presents elements attributable to restoration interventions such as Ti and Zn. Moreover, some gold finishes which were revealed by XRF only in the north wall also seem to be very compromised by restoration. They are present in the columns, in the mirror behind Roxane, and as labile traces in the sleeves' edge of Alexander's blue garment. Further lapis lazuli finishes would also seem by now lost or seriously compromised, as can be seen from the heavy repainting of some mantles, to restore the outlines that are no longer perceptible, including Alexander's dress, which presents elements attributable to restoration interventions such as Ti and Zn. Moreover, some gold finishes which were revealed by XRF only in the north wall also seem to be very compromised by restoration. They are present in the columns, in the mirror behind Roxane, and as labile traces in the sleeves' edge of Alexander's blue garment. Further lapis lazuli finishes would also seem by now lost or seriously compromised, as can be seen from the heavy repainting of some mantles, to restore the outlines that are no longer perceptible, including Alexander's dress, which presents elements attributable to restoration interventions such as Ti and Zn. Moreover, some gold finishes which were revealed by XRF only in the north wall also seem to be very compromised by restoration. They are present in the columns, in the mirror behind Roxane, and as labile traces in the sleeves' edge of Alexander's blue garment.
