Oscar Díaz Santana

Determining the approximate dates that written documents were drawn up based on the chemical composition of the ink is not a simple process. It is very demanding in terms of legal requirements. Various studies have succeeded in dating manuscripts by analyzing the temporal evolutions of the concentrations of dyes and solvents in documents based on the original formulations of the ink pens. These analyses were carried out simultaneously by HPLC-DAD for dyes and by GC-MS for solvents. This study aims, for the first time, to evaluate novel ink compounds and the temporal evolution of the concentrations of the degradation products of the dyes used by most suppliers and which are present in almost all types of ballpoint inks, i.e., Crystal Violet (CV). CV degrades through two parallel pathways: on the one hand, it undergoes progressive demethylation until it becomes pararosaniline, and on the other, it undergoes a breakdown of the molecule obtaining, among other by-products, the compound N,N′-Dimethyl-4-aminophenol (NNAPH), that was experimentally verified using four different inks (e.g., Inoxcrom^® and Sigma^® brands, in blue and black). For the NNAPH compound, we observed that four of the inks under analysis displayed the same temporary behavior despite having different initial chemical compositions. These initial results show the high potential for both CV and NNAPH, together with the rest of the pararosaniline family, as age tracers for dated/old documents. These techniques may potentially open up new avenues for universal dating tools, regardless of the brands of ink employed for use in different ballpoint pen types.

The order of laying down homogeneous intersecting strokes of ball-point inks has been assessed using a range of different spectroscopic and analytical techniques for recent inks and for inks with a time difference of 4 years. These techniques are infrared reflectance photography with luminescence, fluorescence micro-spectrophotometry, Fourier transform infrared spectrometry, high resolution liquid chromatography and gas chromatography with mass spectrometry. This paper presents a combined method applicable to forensic cases aimed at resolving homogenous intersecting strokes of ball-point ink to determine whether they were made at the same time or, on the contrary, they were intersecting strokes laid down with an acute time difference, taking four years as an age reference.