Analysis of the degradation of crystal violet in traces of blue ballpoint pens on paper using statistical and forensic methods under different aging conditions

Crystal Violet (CV), a commonly used triarylmethane dye in blue ballpoint inks, is of interest in chemical ink-dating approaches, yet its degradation kinetics under standardized and environmentally relevant exposure conditions remain underexplored. Here, we quantified CV degradation in ink strokes from three commercial blue ballpoint pens exposed to (i) indoor daylight transmitted through window glass, (ii) dark-storage conditions, and (iii) accelerated xenon-arc aging (ISO 12040). Samples were positioned in accordance with ISO 2810, and CV degradation was monitored by HPLC-DAD via changes in the normalized A(CV)/A₀(CV) peak-area ratio over ten days. All inks showed a pronounced initial decrease in detectable CV under both indoor daylight and xenon-arc exposure, followed by a slower degradation phase, while samples kept in darkness exhibited only minor changes. Meteorological parameters (temperature, cloudiness, and sunshine duration) provided environmental context for interpreting degradation under naturally varying indoor daylight conditions. An exponential decay model provided excellent fits for both indoor daylight and accelerated aging (R2 ≈ 0.97–0.99), describing the observed degradation profiles across inks from different manufacturers.
By combining controlled and environmentally relevant exposures with HPLC-DAD analysis, meteorological data, and kinetic modelling, this study provides a quantitative framework for characterizing CV degradation on paper. The findings demonstrate the strong influence of exposure conditions on CV degradation and support its use as a complementary chemical indicator in forensic ink-aging assessment rather than as an independent measure of chronological ink age.