Minimum requirements for application of ink dating methods based on solvent analysis in casework

Abstract

Several ink dating methods based on solvents analysis using gas chromatography/mass spectrometry (GC/MS) were proposed in the last decades. These methods follow the drying of solvents from ballpoint pen inks on paper and seem very promising. However, several questions arose over the last few years among questioned documents examiners regarding the transparency and reproducibility of the proposed techniques. These questions should be carefully studied for accurate and ethical application of this methodology in casework. Inspired by a real investigation involving ink dating, the present paper discusses this particular issue throughout four main topics: aging processes, dating methods, validation procedures and data interpretation. This work presents a wide picture of the ink dating field, warns about potential shortcomings and also proposes some solutions to avoid reporting errors in court.

Identification of characteristic organic contaminants in wastewaters from modern paper production sites and subsequent tracing in a river

“…2). 2-Phenoxyethanol is commonly found in ballpoint inks, but is also used as a preservative in cosmetic products [22,23].…”

The investigation of dye aging dynamics in writing inks using Raman spectroscopy

“…When ink is applied on paper, a series of processes simultaneously occur: ink drying due to the solvent evaporation, solvent absorption on the surface of the paper and solvent diffusion inside the paper [1], ink fading due to degradation of colorants and ink solidification due to polymerization of resins [1e4]. The degradation of dyes is much slower than many other processes.…”

Situating forensic traces in time

“…Additionally, chemical and physical processes may interfere, so that more complex models generally need to be developed to describe aging reactions (e.g., [31]). …”

“…Situating a trace in time serves the three main purposes of forensic sciences: as information to help investigators [45,46,1], as evidence in court [31], and also in support to more proactive policing framework such as intelligence-led approaches (even for health or other security issues) [47,48]. The interpretation of traces and dissemination of the information both highly depend on the decision-making process which goes well beyond a court trial.…”

“…However, a probabilistic answer based on Bayesian inference of sources, is now generally considered the better approach in forensic sciences [54,55]. Following this guidance, recent works proposed the use of likelihood ratio (LR) to interpret dating evidence for inks [31,56], gunshot residues [57] and a person's age…”