## 3 Results and Discussions
### Micro-FTIR  
The spectra recorded for the three paper samples were compared and the functional groups characteristic of paper [31] were identified (Figure 7). Thus, within the 2000-4000 cm\({}^{-1}\) range, the presence of valence vibrations was identified for OH groups, with a 3333 cm\({}^{-1}\) peak, CH and CH2 with a 2895 cm\({}^{-1}\) peak; the 1500-2000 cm\({}^{-1}\) range shows poor absorption at 1621 cm\({}^{-1}\) due to symmetrical water molecule deformation vibrations (cellulose moisture).  
The 1200-1500 cm\({}^{-1}\) wavelength range contains a series of distinct bands of the CH\({}_{2}\)OH primary alcohol group with peaks at 1427 cm\({}^{-1}\), 1361 cm\({}^{-1}\), 1280 cm\({}^{-1}\) and 1203 cm\({}^{-1}\) due to deformation vibrations. Additionally, the deformation vibrations of the C-O and C-H bonds are found within this same range.  
The 950-1200 cm\({}^{-1}\) range contains the valence vibrations of the C-O, C-C bonds of the pyranose cycles, which peak at 1053 cm\({}^{-1}\), and the deformation vibrations of the CH\({}_{2}\)OH groups. The area ranging from 1430 cm\({}^{-1}\) to 850 cm\({}^{-1}\) is the fingerprint area, which is the most complex [32].  
Within the 750-900 cm\({}^{-1}\) range, the 895 cm\({}^{-1}\) band is due to the deformation vibrations of the CH\({}_{2}\)OH, CHOH groups and pyranose cycles.  
According to the 1508 cm\({}^{-1}\) peak, the paper in the document marked S1 contains lignin, which is absent in documents S2 and S3.  
All samples contain calcium carbonate, as shown by the 1428 cm\({}^{-1}\) peak [5]. The 1315 cm\({}^{-1}\) peak corresponds to C black or amorphous carbon [33].  
The 1683 cm\({}^{-1}\) peak, which is hardly noticeable and visible only for S1, belongs to the C=O band, which indicates cellulose hydrolysis and oxidation [34]. The peaks within the 1430-1350 cm\({}^{-1}\) and 1610-1550 cm\({}^{-1}\) ranges are thought to be generated by the carboxylic salts responsible for paper degradation. The group of absorption bands in the 1400-1200 cm\({}^{-1}\) area corresponds to the crystalline component of cellulose.  
The 895 cm\({}^{-1}\) peak intensity is due to the amount of amorphous cellulose [5; 35].  
Structural organization was assessed by calculating the crystallinity index (I\({}_{\rm c}\)), degree of lateral order extent (G\({}_{\rm OL}\)) and intensity of hydrogen bonds (I\({}_{\rm legH}\)).  
I\({}_{\rm c}\) and G\({}_{\rm OL}\) were determined by calculating the ratio between the absorbances of the bands specific to the crystalline and amorphous ranges of cellulose (1372 cm\({}^{-1}\), 1429 cm\({}^{-1}\) and 2900 cm\({}^{-1}\), 893 cm\({}^{-1}\)), while the I\({}_{\rm legH}\) in the absorption band intensity ratio ranges from 3400 to 1320 cm\({}^{-1}\)[31].  
Table 2 shows the crystallinity index, the degree of lateral order and the intensity of hydrogen. Higher indices are correlated with the presence of larger amounts of type I cellulose.  
The data collected may be correlated with some degradation processes: in microclimate conditions, the evolution of IR parameters reflects the oxidation of amorphous areas.  
When comparing the three ink spectra (Figure 8) with their paper counterparts, we noticed that the former resembled the latter, yet they were slightly flattened or had slightly shifted. Moreover, the 786, 756 and 733 cm\({}^{-1}\) peaks in S3, the 853 cm\({}^{-1}\) peak in S2 and the 1582 cm\({}^{-1}\) peak in S1 may be attributed to ferro-gallic ink.