## 3 Results
### Raman Spectroscopy  
The Raman analysis performed on Posca markers, and the black ballpoint colour reveals peaks associated to both organic and inorganic fractions (Table 9). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Vibrational Mode** & **Black** & **Red** &
\begin{tabular}{c} **Light** \\ **Blue** \\ \end{tabular} & **Blue** & **White** & **Yellow** & **Green** & **Pink** \\ \hline Multiphoton (TiO\({}_{2}\)) & 252 & 262 & 264 & 250 & & 264 & 271 & 257 \\ \hline Lattice mode Si-O-Si & 329 & & & 322 & 327 & & 315 & \\ \hline Lattice mode Si-O-Si & & 345 & 352 & & 357 & 359 & & 352 \\ \hline Eg mode (TiO\({}_{2}\)) & & 452 & 441 & & 450 & 445 & 413 & 452 \\ \hline \(\
u\) Si-O/Al-O & & 483 & 485 & 489 & 503 & 501 & 475 & 543 \\ \hline A1g mode (TiO\({}_{2}\)) & & 613 & 613 & 601 & 613 & 613 & 605 & 615 \\ \hline Macrocyde deformation & & & 682 & 684 & & & 684 & \\ \hline \(\delta\)(C-H)/\(\delta\) aromatic ring & 726 & 738 & & 749 & & & 743 & \\ \hline Aromatic ring breathing & 754 & & 754 & & 782 & & 775 \\ \hline \(\
u\)C-O-C/\(\
u\)C-C-C & & & & & & & \\ /\(\
u\)C-N/macrocyde deformation & 801 & 838 & 819 & & 852 & \\ \hline \(\
u\)C-O-C/benzene breathing & & & & & & 924 & \\ \hline Benzene breathing & & & 1016 & 1002 & & 1005 \\ \hline \(\
u\)(C-C) & & 1030 & & & & & \\ \hline \(\
u\)(C-C) & 1035 & 1040 & 1042 & 1030 & 1028 & 1028 & 1035 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Vibrational bands detected in the coloured areas of the experimental banknote and their corresponding vibrational mode assignments. The black ballpoint colour Raman spectrum shows intense peaks at 424, 522, 622, and 726 cm\({}^{-1}\), related to aromatic ring deformations and C-H bending vibrations, typical of triphenylmethane dyes (Figure 5). The peak at 1172 cm\({}^{-1}\) corresponds to in-plane C-H vibrations in substituted aromatic systems, while peaks between 1532 and 1620 cm\({}^{-1}\) indicate conjugated C=C stretching, characteristic of aromatic molecules like Crystal Violet. Secondary peaks between 800 and 1450 cm\({}^{-1}\) suggest the presence of a solvent, likely benzyl alcohol or phenoxyethanol [96; 97; 98]. The red Posca marker spectrum, dominated by peaks at 738, 1165, 1249, 1290, 1367, 1425, 1456, and 1616 cm\({}^{-1}\), points to an azo pigment with conjugated aromatic systems (Figure S11). Low-frequency peaks at 452 and 613 cm\({}^{-1}\) correspond to rutile-phase titanium  
Figure 5: Raman spectrum collected on black ballpoint ink. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Vibrational Mode** & **Black** & **Red** &
\begin{tabular}{c} **Light** \\ **Blue** \\ \end{tabular} & **Blue** & **White** & **Yellow** & **Green** & **Pink** \\ \hline \(\
u\)(C-H) & 1172 & 1165 & 1149 & 1177 & 1174 & 1165 & 1163 & 1165 \\ \hline \(\delta\)(CH\({}_{2}\))/\(\delta\)(CH\({}_{3}\)) & & 1249 & & 1277 & & & 1279 & 1272 \\ \hline \(\
u\)(C-N=N)/ring C=C & 1335 & 1323 & 1346 & 1344 & & 1335 & 1335 & 1325 \\ \hline \(\
u\)(C-N=N)/ring C=C/\(\delta\) aromatic ring & 1395 & 1374 & 1377 & 1393 & 1435 & 1409 & 1391 & 1395 \\ \hline \(\
u\)(C=C)/\(\
u\)(C-N) & 1532 & 1530 & 1532 & 1530 & 1532 & 1532 & 1530 & 1523 \\ \hline \(\
u\)(C=C) conjugated & 1620 & 1616 & 1609 & 1595 & & 1597 & 1602 & 1611 \\ \hline \(\
u\)(C=O) conjugated & & & & 1655 & & & 1637 & 1650 \\ \hline \(\
u\)(C=O) stretching & & & & & & & 1734 & 179 \\ \hline Overtones & 1825–1946 & & & 1813 & & 1948 & \\ \hline \end{tabular}
\end{table} 
Table 9: _Cont._dioxide, while secondary peaks in the 329-483 range and 522 cm\({}^{-1}\) suggest silica vibration. The region between 1370 and 1450 cm\({}^{-1}\) may also reflect contributions from the acrylic polymer, characterised by C-C and CH vibrational modes [82; 99; 100; 101; 102; 103; 104; 105; 106; 107]. The pink Posa marker shares similarities with the red marker but shows distinct features (Figure S12). Intense peaks at 322, 452, and 615 cm\({}^{-1}\) are related to aromatic ring vibrations and rutile-phase titanium dioxide.