A Nondestructive Approach To Comparing Ink Lines Is Accomplished With reflectance spectroscopy, a technique that measures the amount of light reflected from a surface at different wavelengths. This method allows for the differentiation of inks based on their unique spectral signatures, providing valuable insights in forensic document examination without damaging the original document. This article explores the effectiveness of reflectance spectroscopy, in conjunction with luminescence spectroscopy, for differentiating blue ballpoint pen inks.
Differentiating Inks with Reflectance and Luminescence Spectroscopy
In a study involving 30 blue ballpoint pens, 435 unique ink pairs were compared using both reflectance and luminescence spectroscopy. Reflectance spectroscopy successfully differentiated approximately 88% of the ink pairs, while luminescence spectroscopy differentiated 77%. By combining the results of both methods, the differentiation rate increased to 92%, demonstrating the complementary nature of these techniques.
Figure 1: Differentiation of blue ballpoint ink by applied methods (reflectance and luminescence spectroscopy).
Table 1 below illustrates the final groupings of the blue ballpoint pens after applying both reflectance and luminescence spectroscopy. Several pens shared similar spectral characteristics, indicating potential similarities in ink formulation.
| Group | Pen Code (bb) |
|---|---|
| 1 | 1, 3, 8, 15, 22 |
| 2 | 4, 9, 17 |
| 3 | 6, 7, 10 |
| 4 | 2, 14, 16 |
| 5 | 11 |
| 6 | 23 |
| 7 | 25 |
| 8 | 26 |
| 9 | 5, 21 |
| 10 | 24, 27, 30 |
| 11 | 28, 29 |
| 12 | 12, 13, 18, 19, 20 |
Table 1: Groups of blue ballpoint pens based on combined spectroscopy results.
Comparing Reflectance Spectroscopy Results
Reflectance spectroscopy provides a more objective and straightforward method for comparing ink lines. Figure 2 showcases examples of undistinguishable ink lines (bb1, 3, 8, and 15) with similar spectral shapes and peak wavelengths. Minor variations in signal intensity were attributed to natural variations within the same ink.
Figure 2: Reflectance spectra of undistinguishable ink pairs (bb1, 3, 8, and 15).
Conversely, Figure 3 depicts distinguishable ink lines (bb2, 5, and 9) with distinct spectral features, specifically in the number of peaks and infrared reflectance.
Figure 3: Reflectance spectra of distinguishable ink pairs (bb2, 5, and 9).
Reflectance spectroscopy proved crucial in differentiating inks that lacked luminescence, as seen in Figure 4 with bb6 and 9. This highlights its advantage over luminescence spectroscopy in certain scenarios.
Figure 4: Reflectance spectra of inks without luminescence but differentiated by reflectance spectroscopy (bb6 and 9).
Analyzing Luminescence Spectroscopy Results
While luminescence spectroscopy offers valuable information, it may not always provide definitive differentiation. Figure 5 shows similar luminescence spectra for bb24 and 27, indicating the limitations of this method in some cases.
Figure 5: Luminescence spectra of undistinguishable ink pairs (bb24 and 27).
Figure 6 demonstrates the successful differentiation of bb14, 21, and 26 using luminescence spectroscopy, based on variations in spectral patterns and peak characteristics.
Figure 6: Luminescence spectra of distinguishable ink pairs (bb14, 21, and 26).
Conclusion
A nondestructive approach to comparing ink lines is achieved through reflectance spectroscopy. This method, coupled with luminescence spectroscopy, provides a powerful tool for forensic document analysis, enabling accurate differentiation of inks based on their unique spectral properties. While both techniques have strengths and limitations, their combined use enhances the overall discriminating power and provides a comprehensive analysis for ink comparisons. Reflectance spectroscopy stands out as a particularly valuable tool due to its objectivity and ability to differentiate inks even in the absence of luminescence.
