In situ studies into the characterisation and degradation of blue ballpoint inks by diffuse reflectance visible spectroscopy

Abstract

blue ballpoint inks sourced from Western Australian retailers were deposited onto commercial copy paper and analysed using diffuse reflectance visible spectroscopy. Principal component analysis showed that while several pens were clearly distinguishable based on their visible spectra alone, others exhibited overlap. Linear discriminant analysis was then used to build a chemometric model for the classification of the inks. Using a separate validation set, 71.7% of spectra were correctly assigned to a specific pen, and a further 16.7% to the correct pen supplier. Analysis of six pen inks stored under different conditions found the inks remained chemically stable for at least two months when stored in the dark. However, two inks exhibited spectral changes within one week under ambient light, and all but one ink displayed changes within two months, resulting in altered predictions using the chemometric model. This may be useful in cases of alleged fraud, where it is suspected that an ink entry may have been altered using the same pen at a later date. Artificial ageing experiments found that both heat and ultraviolet light play a role in the ageing process, and that accelerated ageing using these factors gives a reasonable depiction of short-term ageing under natural conditions.

A study into the ageing and dating of blue ball tip inks on paper usingin situvisible spectroscopy with chemometrics

“…All data pre-processing and analysis was performed using the Unscrambler® X 10.4 soware (Camo Soware AS, Oslo, Norway). Previous work investigated the use of the Kubelka-Munk (K-M) conversion, 28 as this is routinely applied to reectance spectra in order to facilitate quantitative analysis. 32,33 However, it was found that the K-M function did not improve overall discrimination, and so this function was omitted in the present study.…”

“…† The deposits were then le to age in three locations representative of typical office environments as per below, with spectra previously recorded at various intervals up until two months. 28 The present manuscript is a continuation of that study utilising the same ink deposits, with additional spectra recorded at 4, 6, 8, 10, 13, 14, 19, 24, 28 and 32 months aer ink deposition.…”

“…In previous work by the authors, 35 blue ball tip pens were obtained from existing stationery supplies and Western Australian retailers (Table S1 †). 28 The sample set was intended to consist solely of ballpoint inks, as ballpoint pens are generally considered to be the most common writing implement in current use. 31 However, during the course of this study it was found that one ink, originating from a Pilot G-2 05 retractable pen, was in fact a gel formulation.…”

“…Ink deposits were analysed by diffuse reectance visible spectroscopy in the same manner described in previous work. 28 Five replicate spectra were obtained for each sample using a Cary 4000 UV-Visible spectrophotometer with a DRA-900 internal diffuse reectance accessory (Fig. S1 †).…”

“…In previous research by the authors Sauzier et al, diffuse reectance visible spectroscopy was utilised with chemometrics to examine the classication and chemical changes upon ageing of blue ball tip inks on paper. 28 As highlighted by Ortiz-Herrero et al, 27 diffuse reectance spectroscopy is highly advantageous for this purpose as it is rapid, requires minimal sample preparation and is non-destructive when applied in situ. A discriminant model was constructed from a sample set of 35 inks using PCA and linear discriminant analysis (LDA), then evaluated using an external validation set of 12 inks.…”