## 3 Results and Discussion

Table 4: The frequencies and shapes of vibrations in Raman spectra recorded for writing ink containing dyes from the triarylmethane group (B-type) and data from the literature corresponding to crystal violet dye. Figure 5: Raman spectra of A-type ink (**left**) and B-type ink (**right**). These Raman spectra were recorded using two laser excitation wavelengths: 785 nm and 532 nm. always requires an evaluation of the quantity of the extracted or evaporated material using another method. The most common methodology used for this purpose is the analysis of micro-fragmentsof handwritten inscription based on densitometry or spectrophotometry [22; 23; 24]. Figure 7 demonstrates comparison of the absorption spectra of writing inks and corresponding individual dyes. The writing ink of type A includes both alcohol-soluble phthalocyanine dye and dyes of the triarylmethane group, whereas their absorption bands are centered at 676 and 620 nm, as well as at 566 nm, respectively. Despite several distinctions in the shapes of the absorption bands, the positions of the absorption maxima of writing inks are to a greater extent governed by the spectral properties of the dye rather than by the spectral properties of other components. Thus, chromatographic studies were performed in combination with spectrophotometric ones. In this regard, the chromatographic peak intensities were normalized to the optical density value of the dye extract in DMF. In order to establish the time intervals of processes connected to the presence of solvents as binding components in writing inks, evaporation in particular, gas chromatographic experiments were carried out undernormal storage conditions and temperature treatment. The obtained results were compared in order to find the optimal conditions for the elimination of volatile components from writing inks. The evaporation dynamics of volatile components were studied in the writing inks listed in Table 6. All samples underwent different regimes of temperature exposure in order to study the influence of temperature on the spectral characteristics of writing inks (Table 7). In addition, the relation of the heating effect withthe effect of storage time at normal conditions was evaluated in order to estimate the rate of chromatographic degradation of the writing inks with respect to spectral degradation. Thus it was found that, upon increasing the temperature, the rate of tetraethylene glycol evaporation also increases. It took about 56 h of heating at 90 degrees in order to completely evaporate the solvent. It is curious that this dependency is exhibited significantly less for glycerol, despite the fact that this solvent is considered to be the most convenient component for chromatographic analysis. Typically, the majority of solvent evaporates after 1.5 months under normal conditions. Glycerol is a more viscous solvent, and, despite the fact that its boiling temperature is lower than that of tetraethylene glycol, the evaporation process may last longer. This interferes with the reliable comparison of storage time at normal conditions and at high-temperature evaporation. The obtained experimental results are consistent with similar studies on writing inks using gas chromatography, supporting the idea that the capability of handwriting dating based on volatile components is limited and the implementation of spectral methods for dye analysis is required. Figure 6: Raman spectra of pure solvents involved in the composition of different types of writing ink. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Writing Ink** & **Ink Pen Type** & **Solvent Studied** & **Retention Time, Min** \\ \hline A & Technical & Tetraethyleneglycol & 13.676 \\ B & Ballpoint & 2-Phenoxyethanol & 10.823 \\ C & Gel & Glycerol & 7.365 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The characteristics of the writing inks chosen for the current work.