## 3 Results and Discussion
### Tin Layer Chromatography (TLC)  
The TLC analysis provides a robust and powerful method for screening dye components within a chemical matrix. The results of the TLC analysis (Figure 7) revealed that the examined samples show a prominent presence of crystal violet dye as the primary organic dye ingredient [9; 24; 27]. The typical chemical structure of the crystal violet dye is shown in Figure S1. The TLC of crystal violet displays four chromatographic zones, even though it is a single substance, as can be seen in Figure 7a. It is worth mentioning that pristine crystal violet dye is photosensitive and it can degrade upon exposure to light. The light-exposed crystal violet can lose a methyl group and form methyl violet dye, which upon further light exposure loses another methyl group forming tetramethylpararosaniline [28; 29; 30; 31]. Consequently, the TLC of the crystal violet reflects the TLC zones correlated with the mother dye and its associated light degradation products. Additionally, many of the studied BP pens contained additional dyes to attain the desired coloration [32]. In addition to findings on the crystal violet, each group exhibited distinct TLC bands. Samples of subgroup I, including the RX1 and RO4, showed a prominent turquoise band with a retention factor (R\({}_{\mathrm{f}}\)) of 0.55, while the PE1 sample slightly displayed that band. On the other hand, the TO1 sample did not show a turquoise-relevant band. The turquoise-relevant band is designated as D1. For subgroup II, the PR2 and RE1a samples demonstrated bands relevant to strong green dye with an R\({}_{\mathrm{f}}\) value of 0.66. This band is designated as D2. The VN1 sample of subgroup II showed deviated behavior from the norm and displayed an outlier band. This outlier band was designated as D5. For the two samples, PK1 and BV1 of subgroup III, a green band with an R\({}_{\mathrm{f}}\) value of 0.76 could be observed for the PK1 sample; this was designated as D3. The BV1 exhibited bands relevant to the D2 dye band similar to samples of subgroup II. The SA1a sample of subgroup IV exhibited a turquoise-relevant band with an R\({}_{\mathrm{f}}\) value of 0.53, designated as D4. This band was observed in both the TO3 and ZR1a samples, but as a faint band only. Figure 6: IRL images of solvated ink samples of subgroups III and IV under white light and different preset optical excitation filters. A summary of the distribution of dye components among the different solvated ink samples of subgroups I-IV is presented in Table 1. The TLC results revealed the prominent presence of crystal violet dye in all solvated ink samples. The samples of subgroup I, except for the TO1 sample, contain the D1 dye. The samples of subgroup II comprised D2 dye, except for the VN1 sample which featured a D5 dye instead of D2. For samples of subgroup III, the PK1 sample contained D3, while BV1 contained D2. Samples of subgroup IV comprised the D4 dye, in addition to the D2 dye in the case of both SA1a and TO3 samples. The TLC plates were then examined by using the VSC to further study the optical behavior of the separated bands on TLC plates and gain insights into the origin of the IRL of the solvated ink samples. The IRL images of the TLC plates of samples of subgroups I-IV under white light and different preset optical excitation filters are displayed in Figures 8 and 9. The two TLC sheets for subgroups I and II were examined together under the ten preset excitation filters. The IRL images shown in Figure 8 indicate that the TLC bands of the reference crystal violet, as well as the correlated bands in the solvated ink samples, show very weak IRL under the first (400-485 nm) band-pass filter. They then began to luminesce from the second (400-535 nm) band-pass filter and luminescence increases over the excitation bandwidths range of the third (445-570 nm) filter to the fourth (485-590) nm filter. The highest luminescence could be observed using the fifth 485-610 nm band-pass filter.