## 3 Results and Discussions
### SEM Analysis  
Simultaneously produced microtopographic images and determined the morphology of surface structure components, while EDX revealed the elemental composition [25]. SEM microphotographs show the specific filaments of cellulose fibers and the filling material (Figure 6a-c). These stand out very clearly, in the form of three-dimensional networks, which can move independently of the others, thus providing good paper flexibility. EDX analysis conducted on the three documents revealed the presence of C, O, Si, Al, Ca and S in all the samples; in addition, the samples marked S2 and S3 also contained Mg, Na, Cl and P (Table 1). Figure 4: OM images of written documents: (**a**) S1; (**b**) S2; (**c**) S3. Figure 5: Migration of the sulfate anion with acid hydrolysis on the back of the page: (**a**) S2 and (**b**) S3. Figure 6: SEM microphotographs of the analyzed documents: (**a**) S1 (\(\times\)500), (**b**) S2 (\(\times\)300), (**c**) S3 (\(\times\)200). Elemental composition revealed the following data and facts:  
* The lack of Mg in sample S1 is proof of the fact that the filling material does not contain talc, a material used to achieve an opaque and smooth paper surface [14]. Calcium carbonate (CaCO\({}_{3}\)) was used as a filler, which was also confirmed by the characteristic band within the 1400-1500 cm\({}^{-1}\) range revealed by micro-FTIR analysis (Figure 7). Calcium carbonate stabilizes the carboxylic groups of cellulose and makes it possible to increase paper aging stability [25]. * The presence of Si and Al accounts for the use of kaolinite (Al4[(OH)8 | Si4O10]) to increase paper opaqueness and whiteness, which was also confirmed by the 1029 cm\({}^{-1}\) peak. Sample S1 has the smallest amount of kaolinite. * Documents S2 and S3 were treated with calcium hydroxide and with lye/caustic soda (NaOH), which is accounted for by the Ca and Na contents. Saponified rosin glue mixed with aluminum sulfate and added with alum, is demonstrated by the presence of: Na, Al and S. Saponified rosin glue may have been used as gluing agent, as it was commonly used between 1807 and 1880 [23]. This gluing system provides alkaline conditions. After 1876, aluminum sulphate was used, which is thought to be the main source of acidity in paper (the pH is 3.8 to 4.5). Aluminum sulphate hydrolyses, and the result of this hydrolysis process is the hexahydro-aluminum acid complex [26] and sulphuric acid which has a strong destructive effect on cellulose fibers [27; 28]. Acidity also occurs during paper bleaching treatments, due to the oxidation products in lignin. Alum was used as a mordant, an assumption proven by the presence of Al and S. The use of aluminum in paper manufacturing is one of the main causes of paper degradation. Aluminum compounds have been used to reduce the hydrophilic character of paper. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{8}{c}{**Elemental Composition in Gravimetric Percentages (\%)**} \\ \cline{2-11}  & **C** & **O** & **Si** & **Al** & **Ca** & **Mg** & **Na** & **P** & **Cl** & **S** \\ \hline S1 & 36.62 & 60.50 & 0.42 & 0.77 & 1.02 & - & - & - & - & 0.67 \\ \hline S2 & 29.93 & 63.02 & 1.01 & 1.59 & 0.67 & 0.93 & 1.39 & 0.42 & 0.58 & 0.46 \\ \hline S3 & 30.92 & 62.52 & 1.08 & 1.84 & 0.72 & 0.70 & 1.25 & 0.27 & 0.32 & 0.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Elemental composition of the three documents. Figure 7: FTIR spectra on the paper medium of the three documents: (a) S1; (b) S2; (c) S3. In concentrations higher than 610 ppm [29; 30], they hydrolyze and contribute to the acidification of paper, which causes cellulose embrittlement and leads to poorer crystallinity (depolymerization). On the other hand, calcium and magnesium have positive effects on cellulose stability.