## 3 Results
### Black  
Under microscopic examination, samples taken from the black paint areas of all four masks appeared instead a homogeneous, translucent brown color, and without any discernible black particles (Figure 3A). FTIR analysis showed very similar profiles, and comparison with published databases suggested the black material to be a type of tannin, a plant-derived polyphenic compound. Most bands in the spectra could be related to the FTIR profile of tannic acid, including the OH stretching of hydrogen bonds at 3300 cm\({}^{-1}\)  
Figure 2: (**left**) Detail of white and black paint, lower PR front side (1970.103), with plant fibers indicated by an arrow, and (**right**) detail of red and black paint, front side (2008.190).  
the C=C stretching of the benzene ring at 1709 cm\({}^{-1}\) (less intense in the samples' spectra than in the reference spectrum for tann acid), the C-C stretching and C-H deformation of benzene ring at 1612 and 1535 cm\({}^{-1}\), a sharp band at 1447 cm\({}^{-1}\) from the C-C stretching of the benzene ring, two intense and broad bands at 1348 and 1221 cm\({}^{-1}\), and another sharp band at 1033 cm\({}^{-1}\) (Figure 3B) [11]. The spectra did not exhibit any additional bands attributable to the common classes of natural (e.g., protein, polysaccharide, or plant oil) or synthetic organic materials that might function as paint binders, suggesting that the paint is a relatively pure tannin-based material. Results of Py-GCMS analysis supported the FTIR data, showing a series of compounds consistent with plant tannins. A representative chromatogram, of sample S1 from the Hawk mask (1970.103), is dominated by the methyl derivatives of phenolic and polyphenic compounds including gallic and ellagic acids, together with the methyl derivative of the cyclic polyalcohol myo-inositol (Figure 3C).  
While these analyses allowed us to determine the nature of the coloring material in the black paint, further experiments were undertaken to corroborate its source as reported in the literature. Following [PERSON]'s descriptions of the preparation of the so-called \"thick black\" paint [1], seed pods from _Acacia nilotica_ were placed in a beaker, covered with distilled water, and boiled on a hot plate for 8 h (Figure 4A-C).  
Figure 3: **(A)** microphotograph of black sample S1 from the Fish mask (1958.116) under visible light; **(B)** FTIR spectra of (a) black sample S1 from the Hawk mask (1970.103), (b) _Acacia nilotica_ seed pod dried brown extract (8 h), (c) reference spectrum of a tann acid (IRUG database, OD00186 [12]); **(C)** Py-GC/MS data (total ion chromatogram) of (a) sample S1 from the Hawk mask (1970.103), (b) _Acacia nilotica_ seed pod dried brown extract (8 h).  
An aliquot of the brown extract was then dried and analyzed by FTIR and Py-GCMS. Results were very similar to those obtained for samples from the masks, with the FTIR profile (Figure 3B) closely resembling that of tannic acid, and the methyl derivatives of gallic acid, myo-inositol and other hydroxybenzoic acids identified by Py-GCMS (Figure 3C). While these results do not allow us to specifically determine seed pods from _Acacia nilotica_ to be the source of the black paint, since tannins are widespread in various types of plants, they nonetheless support the accounts of the source of the paint and its manner of preparation.