## 3 Results and Discussion  
### Chemical Analysis  
The chemical compositions of recently cut and archaeological wood samples are shown in Table 1. As can be seen, the amounts of holocellulose in recently cut elm and poplar were, respectively, 80.01% and 81.46%, while these amounts were significantly lower in archaeological elm and poplar, which were 56.45% and 51.18%, respectively. The amount of holocellulose in hardwood species are generally between 59% to 85%, and it changes considerably at different tree age and growing location [34]. The reduction of holocellulose content in archaeological wood samples was widely reported previously [34; 35; 37; 38; 39]. It can be due to the degradation of polysaccharides at the initial stage of the ageing process [6; 34; 40]. The amount of lignin in the archaeological samples was significantly higher than in the recently cut samples, which is mainly attributed to the loss of other wood compounds, e.g., holocellulose [1; 6; 41]. The extractive content of the archaeological elm and poplar were 2.50% and 3.55%, respectively, while these values for the recently cut samples were 1.26% and 1.48%, respectively. This significant difference can be due to the breakdown of wood polysaccharides into leachable monosaccharides or oligosaccharides articles during degradation processes [3; 4]. Similar results were reported previously by [PERSON] et al. [42] for archaeological cypress wood. The ash contents in archaeological elm and poplar were 4.70% and 3.18%, respectively, and the recently cut samples showed a respective ash content of 0.65% and 0.61 for the elm and poplar samples. The differences were statistically significant (ANOVA, \(p\) < 0.05). There is a significantly higher amount of ash content in the archaeological wood samples. The deposition of inorganic elements in the wood structures during the service life and storage periods might be an additional reason. These findings are almost in agreement with the previous studies on the chemical compositions of archaeological oak and elm wood samples [43; 44; 45; 46]. FTIR spectroscopy was used to analyze the changes in the chemical structure of archaeological wood samples due to the storage and ageing process. Figure 2a,b illustrates the FTIR spectra of recently cut and archaeological elm and poplar wood samples. The absorption band between 3300 and 3400 cm\({}^{-1}\) was assigned to the stretching vibration of the -OH group [5; 46; 47]. This band was identical in both recently cut and archaeological elm samples, while it was slightly decreased in the archaeological poplar. The stretching vibration in the region between 2800 to 3000 cm\({}^{-1}\) is associated with the -CH group in cellulose, hemicellulose, and lignin [5; 43]. The band at 1733 cm\({}^{-1}\), which is assigned to the stretching vibrations of the unconjugated C=O group and specific moieties, such as esters, had disappeared in the archaeological elm and poplar. This could be related to the strong degradation of hemicelluloses after the ageing process [41; 45; 48]. Both archaeological elm and poplar samples exhibited considerably higher absorption in the region between 1235 and 1646 cm\({}^{-1}\). These vibrations were mostly attributed to the stretching of the C=C and C=O groups in the lignin structure [6; 49]. The _LI_ values in both archaeological elm and poplar were strongly increased, i.e., from 0.71 and 0.82 in recently cut elm and poplar to the respective values of 1.67 and 1.40 in the archaeological samples. Similar results were