## 3 Results
### Wood Deterioration
The latter shows the characteristic infrared features of woods, but with some significant differences if compared with the standard one. The broad band in the 1180-930 cm\({}^{-1}\) range (Figure 7b, green rectangular selection labelled with \(\lx@sectionsign\)) is attributed to C-O, C-O-C, and C-C stretching vibrations of carbohydrates and can be assigned to the presence of cellulose and hemicellulose [63]. This band shows a very intense signal with a broad shape in the standard wood. In sample #1, a slight decrease in the absorption signal was accompanied by a sharpening of the infrared features, while sample #2 showed a further decrease in the intensity with a strong loss of the characteristic band shape. The bands at 1509 cm\({}^{-1}\) (Figure 7b, orange rectangular selection labelled with \(\#\)) can be attributed to C=C stretching in guiaacyl rings, one of the main moieties of lignin, and were used for mapping the distribution of this wood component [65]. A decrease in the signal of this band was observed for both samples #1 and #2. In the spectral range of 1480-1180 cm\({}^{-1}\), several infrared features were present. They can be assigned to both cellulose/hemicellulose (i.e., the band at around 1320 cm\({}^{-1}\) was due to the C-H bending of this molecule) and lignin (i.e., the band at around 1270 cm\({}^{-1}\) was attributed to C-O stretching) [30]. This spectral range showed a broadening and a decrease in the infrared feature definition that can be linked to a decrease in the structural order of the wooden tissues in the archaeological woods when compared to the standard one. This had already been observed by several authors [30; 66]. Finally, a strong increase in the infrared signal in the 1800-1530 cm\({}^{-1}\) range was detected in the archaeological wood fragments when compared to the _Acacia_ one (Figure 7b, blue rectangular selection labelled with \(\divide\) ). Infrared features in this range are usually attributed to C=O stretching vibrations of esters, ketones, and aldehydes (in particular at higher frequencies). Moreover, the bending vibrations of -OH and the COO\({}^{-}\) stretching vibrations can fall at around 1640 and 1600 cm\({}^{-1}\), respectively. The spectrum of the standard wood (Figure 7b, black line) showed a peak at around 1730 cm\({}^{-1}\). It shifted at around 1711 cm\({}^{-1}\) in the #1 and #2 samples, while the broad peak at about 1610 cm\({}^{-1}\) strongly increased in intensity in the ancient samples. These bands could have been due to carbonyl stretching vibrations in carboxylic acids and carboxylic acid salts and can be attributed to a wood deterioration product increase originating from both hydrolysis and oxidative processes of cellulose [63; 67]. The above-mentioned bands are fundamental for observing the distribution and to quantify the relative percentages of cellulose, lignin, and their deterioration products in the archaeological woods. Unfortunately, the intense peak of weddellite at 1640 cm\({}^{-1}\) (Figure 4e) perfectly matched in the 1800-1530 cm\({}^{-1}\) range, with the band identified to be diagnostic of the formation of wood deterioration products. To avoid an overestimation of the deterioration product presence, the pixels corresponding to the oxalate crystals in sample #1 were cut out by the Quasar software [52]. Then, the FPA false colour maps (Figure 8a) were obtained by integrating the areas of the bands attributed to cellulose, lignin, and the deterioration products as described above and highlighted by the rectangular selections in Figure 7b. As expected, as shown in Figure 8a, the false-colour FPA images of the _Acacia_ standard sample showed the highest amounts (corresponding to the red colour in the maps and the scale bar) of cellulose and lignin (Figure 8b, orange and green rectangles, respectively) and the lower amount of deterioration products (Figure 8a, blue rectangle).