Ink dating, part I: Statistical distribution of selected ageing parameters in a ballpoint inks reference population

A common framework to situate digital and physical traces in time

In this article, three main approaches to situate forensic traces in time were revisited under the prism of the Sydney Declaration and adapted to be applicable to a large range of physical and digital traces. The first approach is based on time tags which are time-based characteristics produced as the result of an activity at a specific time. They can either be directly related to time (i.e., time stamps) or indirectly (i.e., time indicators). While relatively straightforward, time tags require scientific knowledge to be correctly interpreted and to account for the risks of desynchronisation, anomalies and manipulation. The second approach is based on time dynamics and aim at measuring changes that occur as a function of time, such as caesium pulsation (i.e., on which international atomic time is based) or body cooling after death (i.e., from which time since death can be inferred). However, time dynamics phenomena are generally also influenced by other case-specific factors (e.g., environmental factors), and thus more difficult to reliably implement in practice. Finally, the third approach relies on relative sequences, using information unrelated to time, such as relative positions or dynamics of traces at the scene. As each approach has its potential and limitations, a combination of traces from different (both material and digital) sources and approaches is recommended to answer time questions in practice (When? How long? In which succession?) and enhance the reliability of the dating endeavours. It is strongly recommended to consider the principles of the Sydney Declaration when implementing or developing dating methods, as they point at potential issues that are often forgotten in forensic research and practice, such as uncertainties linked to the concept of trace, scene investigation, the asymmetry of time, the importance of context and the multiplicity of purposes. Future research should focus on improving the reliability of these dating approaches by combining and systematising their usage in investigative practice, as well as in broader intelligence processes.

GC-MS Silylation Derivative Method to Characterise Black BIC® Ballpoint 2-Phenoxyethanol Ratio Evaporation Profile-A Contribution to Ink Ageing Estimation

One of the major challenges in forensic document analysis is estimating the age of ink deposition on a manually written document. The present work aims to develop and optimise a methodology, based on the evaporation of 2-phenoxyethanol (PE) over time, that can contribute to ink age estimation. A black BIC^® Crystal Ballpoint Pen was purchased in a commercial area, and ink deposition began in September 2016 over 1095 days. For each ink sample, 20 microdiscs were subjected to n-hexane extraction in the presence of an internal standard (ethyl benzoate) followed by derivatisation with a silylation reagent. A gas chromatography-mass spectrometry (GC/MS) method was optimised for PE-trimethylsilyl (PE-TMS) to characterise the ageing curve. The developed method presented good linearity between 0.5 and 50.0 μg mL^-1, as well as limits of detection and quantification of 0.026 and 0.104 μg mL^-1, respectively. It was possible to characterise PE-TMS concentration over time, which reveals a two-phase decay behaviour. First, there was a substantial decline between the 1st and the 33rd day of deposition, followed a by a stabilisation of the signal, which allowed to detect the presence of PE-TMS up to 3 years. Two unknown compounds were also present and allowed to identify three dating time frames for the same ink stroke: (i) between time 0 and 33 days, (ii) between time 34 and 109 days, and (iii) more than 109 days. The developed methodology allowed to characterise the behaviour of PE over time and to establish a relative dating of three-time frames.

Comparative analysis of aged documents by desorption electrospray ionization-Mass spectrometry (DESI-MS) imaging

Document dating is an important and challenging task in the field of forensic science. With the development of analytical techniques, related methods are emerging for document dating studies. Desorption electrospray ionization-mass spectrometry (DESI-MS) is an ambient ionization-MS technique that has been applied in the forensic discrimination of inks. This study focused on utilizing DESI-MS to distinguish between ink entries of different ages. Blue ballpoint ink and black gel ink samples were artificially aged by heat and light exposure and then screened by DESI-MS in the positive ion mode, with a methanol-water-formic acid solution (90:10:0.1%, v/v/v) as the desorption solvent. As a result, the artificially aged ink samples were directly differentiated from the reference ones in the chemical images of age-dependent compounds such as basic dyes or polyethylene glycol derivatives. The amount of ethoxylated fatty amine surfactants in copy paper was also found to decrease after artificial aging. Moreover, this method enabled us to visualize the differences between the composition of naturally aged and fresh ink samples. It has been proven to cause no apparent destruction of the samples. The identification of chronological changes in document materials suggests that the DESI-MS method is a promising approach for relative document dating.

Non-destructive analysis the dating of paper based on convolutional neural network

A non-destructive method based on Fourier Transformed Infrared Spectroscopy (FT-IR) was proposed to estimate the date of paper from different years in this article. For the paper samples, dated from 1940 to 1980, naturally aged and conserved in library. Partial least squares-discriminate analysis (PLS-DA), Logistic regression and convolutional neural network (CNN), were employed to evaluate the date of paper, with the accuracy 60.74%, 95.31% and 98.77%, respectively. Based on the characteristics of CNN model and with the help of network localization, active variables could be recognized in the whole spectrum. Although the localization of active variables showed a discriminative pattern, the selected spectral regions were similar. Most important variables focused on the 1700-1400 cm^-1, were corresponding to cellulose crystallinity, which was consisted with the ageing processing. The present work gave the potential of FT-IR combined with chemometric techniques could estimate the dating of unknown paper. Meanwhile, the analysis of active variables obtained further indicated the worthy of CNN model for document dating.

Interpol review of questioned documents 2016-2019

This review paper covers the forensic-relevant literature in questioned documents from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol Review Papers 2019.pdf.

Preliminary Studies on the Absorbance Ratio Method Used to Determining the Age of Stamp-pad Ink Seal

Stamp-pad ink seals are often placed on important documents, and determining the dating of stamp-pad ink seal is important to assess the authenticity of a document. In this study, 20 different brands and types of stamp-pad inks were classified by ultraviolet visible spectrophotometer. Six different brands and types of papers were classified by micro-Fourier transform infrared spectrometer and visual spectral comparator 6000. Three different brands of stamp-pad inks and two different types of paper were used to make diachronic samples of the seals. A method was employed to date the stamp-pad seals by comparing absorbance ratios and inks of known age. Curves were created to show the relationship between the absorbance ratio of ink and the age of the seals. The experimental results showed that the absorbance ratio method was applicable for the relative dating of stamp-pad ink seals in some cases where the seal was placed on the document within 10 weeks.

On the behavior of certain ink aging curves

This work treats writing inks, particularly ballpoint pen inks. It reviews those ink aging methods that are based on the analysis (measurement) of ink solvents (e.g., 2-phenoxyethanol, which is the most common among ballpoint pen inks). Each method involves measurements that are components of an ink aging parameter associated with the method. Only mass independent parameters are considered. An ink solvent from an ink that is on an air-exposed substrate will evaporate at a decreasing rate and is never constant as the ink ages. An ink aging parameter should reflect this behavior. That is, the graph of a parameter's experimentally-determined values plotted against ink age (which yields the ink aging curve) should show this behavior. However, some experimentally-determined aging curves contain outlying points that are below or above where they should be or points corresponding to different ages that have the same ordinate (parameter value). Such curves, unfortunately, are useless since such curves show that an ink can appear older or younger than what it should be in one or more of its points or have the same age in two or more of its points. This work explains that one cause of this unexpected behavior is that the parameter values were improperly determined such as when a measurement is made of an ink solvent that is not completely extracted (removed) from an ink sample with a chosen extractor such as dry heat or a solvent.