Spectroscopic and Chromaticity Examination of Disappearing Ink

Abstract

The increasing prevalence of disappearing ink pens in forgery cases has posed significant challenges to forensic document examiners. This study investigates disappearing ink's spectroscopic and chromaticity characteristics to establish a reliable method for determining the relative age of writing. Using a Video Spectral Comparator (VSC-6000/hs), the absorbance, reflectance, and fluorescence spectra of disappearing ink were analyzed over time. Chromaticity values were evaluated within the CIE L*a*b* color space to quantify changes in the ink's optical properties as it faded. Results demonstrate that the L* value, representing luminance, showed a strong correlation with time in absorbance and reflectance spectra (R² = 0.82 and 0.81, respectively). Statistical analysis confirmed the linearity of L* values, making it a significant indicator for estimating the time elapsed since writing. The study concludes that absorbance and reflectance measurements are more effective than fluorescence for analyzing disappearing ink. This research provides forensic experts with a sensitive, non-destructive, and reproducible method to analyze disappearing inks and estimate the relative time of writing, offering a valuable tool for addressing forgery-related challenges.