Discriminating blue ballpoint pens inks in questioned documents by Raman imaging and mean-field approach independent component analysis (MF-ICA)

In the present work, Raman spectroscopy and chemometrics tools were explored as an analytical method to discriminate blue pen strokes on common office paper and bank check paper. The sample set was constituted of blue ballpoint pen inks available on local market and promotional pens as well. The samples were prepared to simulate an adulterated document using different pens. The proposal methodology was based on Raman imaging spectroscopy and Independent Components Analysis algorithm, which were able to recover the original spectrum of each pen, as well as images containing special information about each of the pens used. All recovered spectra could be match with references spectra at least with 0.8572 of correlation coefficient, while recovered images left no doubt about whether a forgery occurred. At the end of analysis, all the examined cases could be solved based on the discrimination between the pens inks, without any prior information.