Elsevier

Science & Justice

Volume 58, Issue 1, January 2018, Pages 17-30
Science & Justice

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

https://doi.org/10.1016/j.scijus.2017.08.002Get rights and content

Highlights

  • Three new ink dating ageing parameters tested based on natural ageing and/or solvent loss.

  • Data acquired and shown for 25 ballpoint pen inks.

  • Statistical treatments performed in order to evaluate the potential of ageing parameters.

  • Comparative and critical studies of the ageing parameters in a forensic perspective

Abstract

The development of ink dating methods requires an important amount of work in order to be reliably applicable in practice. Major tasks include the definition of ageing parameters to monitor ink ageing. An adequate parameter should ideally fulfil the following criteria: it should evolve as a function of time in a monotonic way, be measurable in a majority of ink entries, be as accurate and reproducible as possible, and finally it should not be influenced too much by transfer and storage conditions. This work aimed at evaluating the potential of seven ageing parameters for ink dating purposes: the phenoxyethanol quantity, relative peak areas (RPA), three solvent loss ratios (R%, R%*, NR%) and two solvent loss parameters (RNORM, NRNORM). These were calculated over approximately one year for 25 inks selected from a large database to represent different ageing behaviours. Ink entries were analysed using liquid extraction followed by GC/MS analysis. Results showed that natural ageing parameters (NR% and NRNORM) were not suitable ageing parameters for ink entries older than a few weeks. RPA used other compounds present in ink formulations in combination to PE in order to normalise the results. However, it presented particular difficulties as they could not be defined for all inks and were thus applicable only for 64% of the studied inks. Finally, the PE quantity, R% and RNORM allowed to follow the ageing of the selected inks over the whole time frame and were identified as the most promising. These were thus selected to test three different interpretation models in the second part of this article. The possibilities and limitations of ink dating methods will be discussed in a legal perspective.

Introduction

Ink dating remains a particularly challenging forensic task. Despite almost a century of research [1], [2], [3], [4], only few methods have been reported as being used in practice [5], [6], [7], [8], [9], [10], [11]. This can mainly be explained by the complexity of the ageing processes and the amount of experiments needed to correctly interpret the results in actual caseworks. Several steps were previously described as minimum requirements to reliably estimate the age of an ink entry [12]: method development and validation, ageing parameters selection, data collection under different influencing factors and finally, data interpretation in a legal perspective. Indeed, a method must first be developed and validated in order to insure reliable and sensitive analysis of selected ink ageing parameters over time. This step generally represents the easiest task and is well described in the (forensic) literature [13]. More recently proposed approaches focused on the analysis of ink volatile compounds, and mainly phenoxyethanol (PE) and its decrease over time [5], [6], [7], [8], [9], [10], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32]. While gas chromatography coupled to mass spectrometry (GC/MS) was mainly used to analyse PE and other ink solvents, high performance liquid chromatography (HPLC) was also recently proposed to simultaneously analyse dyes and solvents [10], [11], [23]. Different extraction methods were also proposed such as liquid extraction [6], [8], [9], [12], [21], [22], [25], [26], [27], [29], [31], [32], thermodesorption [7], [18], [24], [33] or solid phase microextraction (SPME) ([17], [19].

Once the method is developed and validated, ageing parameters must be selected to monitor ageing according to the following criteria [12], [25], [34]:

  • -

    they must evolve as a function of time in a monotonic way (ascendant or descendent). The ageing must be measurable over a large time scale (ideally months to years for ink dating).

  • -

    they must be measurable in most ink formulations using the chosen method. It is generally known that ink composition has a significant influence on ink ageing [7], [31]. Thus, analysing representative ink reference populations is essential to insure that the selected ageing parameter can be implemented in most cases.

  • -

    they should be as reliable as possible yielding precise and accurate measurements, ideally even on different ink specimens of the same age.

  • -

    they should be influenced as little as possible by external factors typically encountered in caseworks (such as paper properties, transfer and storage conditions).

In a previous paper using liquid extraction followed by GC/MS [25], four ageing parameters were tested over time under different influence factors: the quantity of PE, different relative peak areas (RPA) and solvent loss ratios using two samples of the same ink entry, one of them artificially aged. These ratios were calculated from the quantities of PE (R%) or from the RPA values (R%*). While data was collected on a limited ink population (n = 3), obtained results were promising. RPA proved to be the most repeatable ageing parameter and the least influenced by the different tested conditions, the solvent loss ratios were the less reproducible parameters.

Finally, an adequate interpretation model must be developed to estimate the age of a questioned ink entry in a legal perspective. Several constraints are attached to this task such as the fact that the “source” ink or pen is generally unknown and thus, a representative ink population has to be considered to adequately interpret the results.

In this article, liquid extraction followed by GC/MS was used to analyse samples from 25 different inks provided by the LKA Münich. These were selected from a large ballpoint pen ink collection as representative of the ageing behaviours measured in previous studies [7], [35]. Ink lines were aged from 4 to 304 days on paper before analysis. Seven ageing parameters, including the PE quantity, the relative peak areas (RPA), three solvent loss ratios (R%, R%*, NR%) and two solvent loss parameters (Rnom and NRnom) were calculated. The first part of this paper focused on the evaluation of the collected data. The distribution of each ageing parameters over time was used to estimate their potential for ink dating purposes. The second part of this paper focused on testing different interpretation models on selected ageing parameters in order to reliably estimate the age of an ink entry in a legal perspective.

Section snippets

Material

Chloroform (99.9%) was purchased from Sigma Aldrich (Darmstadt, Germany). The reference substances phenoxyethanol (PE) 99.5%, benzyl alcohol 98% and heneicosane were purchased from Fluka (Buchs, Switzerland) and the internal standard was deuterated phenoxyethanol (PE-D2) from EGT Chemie (Tägerig, Switzerland),

For sample preparation, 1.5 ml vials, 300 μl and 50 μl inserts as well as springs were obtained from Swiss Lab (Basel, Switzerland).

Samples

The analysed samples were drawn with 25 different inks

Ink population composition

As expected, different ink formulations were observed for the 25 inks of the reference population using GC/MS (Table 1). 19 compounds were identified with the help of the NIST library in 4 days old samples. Among them, well known ballpoint pen ink volatile components were found such as benzyl alcohol (BA), hexylene glycol (HG), 2,2-ethoxyethoxyethanol (EEE), dipropylene glycol derivates (DGP 1, 2 and 3), phenoxyethanol (PE) and phenoxyethoxyethanol (PEE) [9], [25], [26], [31], [43], [44], [45].

Conclusion

This paper presented the ageing curves obtained from 25 ballpoint pen entries over one year. Seven ageing parameters were calculated, among these, four were previously proposed in the literature:

  • 1)

    the phenoxyethanol quantity (PE)

  • 2)

    the solvent loss ratio based on artificial ageing (R%)

  • 3)

    the solvent loss based on artificial ageing (RNORM)

  • 4)

    the solvent loss ratio based on natural ageing (NR%)

  • 5)

    the solvent loss based on natural ageing (NRNORM)

  • 6)

    the relative peak areas between compounds (RPA)

  • 7)

    the solvent loss

Acknowledgements

The authors wish to thank Dr. J. Bügler and Ms. A. Linder from the Landeskriminalamt of Munich for sharing their collection of ballpoint pen inks as well as for their precious help and availability.

The authors also wish to thank the Swiss National Foundation for its support in the frame of this research (no. PP00P1_123358 and PP00P1_150742).

References (49)

  • A.A. Cantú

    Evaporation of a non-ideal solution and its application to writing ink aging

    Forensic Sci. Int.

    (2015)
  • V. Aginsky

    Determination of the age of ballpoint pen ink by gas and densitometric thin-layer chromatography

    J. Chromatogr. A

    (1994)
  • R.L. Brunelle et al.

    Advances in the Forensic Analysis and Dating of Writing Ink

    (2003)
  • R.L. Brunelle et al.

    The dating of inks

  • C. Weyermann

    Dating a document

  • V.N. Aginsky

    Ink aging testing-Do preceding indentation examinations affect ink aging parameters

    J. Am. Soc. Questionned Doc. Examiners

    (2014)
  • V. Aginsky

    Dating and characterizing writing, stamp, pad, and jet printer inks by gas chromatography/mass spectrometry

    Int. J. Forensic Doc. Examiners

    (1996)
  • J.H. Bugler et al.

    Age determination of ballpoint pen ink by thermal desorption and gas chromatography-mass spectrometry

    J. Forensic Sci.

    (2008)
  • M. Gaudreau et al.

    Essentials of the solvent loss ratio method

  • M. Gaudreau et al.

    Ink dating, a solvent loss ratio method

  • D. Kirsch et al.

    A new approach for dating of ballpoint ink entries

  • A. Hahn et al.

    Ink dating by solvents, resins and binders

  • V.N. Aginsky

    Some new ideas for dating ballpoint inks-a feasibility study

    J. Forensic Sci.

    (1993)
  • V.N. Aginsky

    Current methods for dating ink on document

  • Cited by (17)

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

      2021, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
    • Interpol review of questioned documents 2016–2019

      2020, Forensic Science International: Synergy
      Citation Excerpt :

      By the determination of the dye formulation of a sample and by comparison with a database of ink formulation over time, Costa K. and al estimated the date on which manuscripts were launched on documents but with important dating errors (8–15 years). Five studies [67–71] focused on the analysis by GC/MS of phenoxyethanol (PE) of ballpoint inks and, its decrease over time. Koenig A. and Weyermann C [67,68].

    • In the pursuit of the holy grail of forensic science – Spectroscopic studies on the estimation of time since deposition of bloodstains

      2018, TrAC - Trends in Analytical Chemistry
      Citation Excerpt :

      Therefore, in order to apply the same parameter in dating studies of different objects within the same category, the relation between the ageing indicator and the TSD should remain the same, regardless of the initial constitution of the deposited material. To ensure that the changes of the selected ageing parameter are immune to alterations in the initial composition of the trace, analysis of the representative reference populations should be performed [168]; it should show reproducible changes over time to enable precise and accurate measurements;

    • Comparison of the main dating methods for six ball-point pen inks

      2018, Microchemical Journal
      Citation Excerpt :

      Mineral dyes (inorganic) are photo-stable, while organic dyes are photo-labile [61,62] (Fig. 2). Document dating methodologies based on analysing inks have focused on the processes of degradation of the dyes to establish age curves based on their relative concentration in comparison with the PE solvent, by studying the changes that occur in the ratios over time [9,10] (Table 6). These are divided depending on the theoretical base of the dating method.

    View all citing articles on Scopus
    View full text