Use of Raman spectroscopy and chemometrics to distinguish blue ballpoint pen inks  Flávia de Souza Lins Borba, Ricardo Saldanha Honorato, Anna de Juan  Forensic Science International  Volume 249, Pages 73-82 (April 2015) DOI: 10.1016/j.forsciint.2015.01.027 Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 1 Analysis by video spectral comparator by visual inspection. Identification of numerical value alteration, (from $1000.00 to $70,000.00), using a 647nm bandpass filter. Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 2 Raw Raman spectra collected on ink lines. Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 3 (a) Three raw Raman spectra per each ink class before applying preprocessing, (b) mean spectra per each class after applying Savitzky–Golay second derivative (second order polynomial, 21 points window) and normalization. Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 4 Scores plot from PCA model built on the Raman preprocessed spectra of ink samples for: (a) 14 ink classes dataset (original data) (b) samples from C cluster in scores plot in (a) and (c) samples from D cluster in scores plot in (a). Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 5 Tree structure built based on local PCA models performed on Raman preprocessed spectra of the ink samples. Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 6 (a) Dendrogram obtained from Ward's cluster analysis method on Raman preprocessed spectra of ink samples and (b) enlarged view of dendrogram for distance values around 100. Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions

Fig. 7 Relevant spectral regions for discrimination among ink classes (as pointed out by VIPs values) together with mean spectra of ink classes preprocessed with Savitzky–Golay for a better comparison. Forensic Science International 2015 249, 73-82DOI: (10.1016/j.forsciint.2015.01.027) Copyright © 2015 Elsevier Ireland Ltd Terms and Conditions