Ink Testing

Finšgar, Matjaž, and Katja Andrina Kravanja. Microchemical Journal 205 (2024): 111425.

This study explores the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with multivariate statistical analysis to differentiate blue pen inks in document forgery investigations.

ToF-SIMS analysis was performed on strokes from six commercially available blue pens, with the data analyzed using principal component analysis (PCA) and multivariate curve resolution (MCR). PCA successfully reduced the complexity of the ToF-SIMS data, allowing for clear differentiation of the inks. The first three principal components captured the majority of the variance, and the PCA score plots showed distinct clusters corresponding to each pen's spectra. PCA analysis of large-area ToF-SIMS images also highlighted characteristic spatial patterns in the pen strokes, though it was less effective for identification purposes.

In contrast, MCR provided a more chemically intuitive approach by isolating pure component spectra from complex mixtures. Each MCR factor was linked to a specific pen, enabling precise identification of the pen stroke. MCR score images revealed clear correlations with individual pen strokes, and the loadings identified characteristic m/z signals specific to each pen.

Koochakzaei, Alireza, and Tahereh Ghaffari. Vibrational Spectroscopy 127 (2023): 103545.

This study aims to identify different types of traditional black inks using molecular spectroscopy and spectral imaging methods.

Six types of black inks—carbon, iron-gall, carbo-gall-vitriol, carbo-gall-alum, peacock, and starch—were prepared using traditional recipes and subsequently analyzed using Raman spectroscopy, FTIR spectroscopy, micro-spectrophotometry, FORS, technical imaging, hyperspectral imaging, and SEM. The results showed that Raman spectroscopy effectively distinguishes between carbon-based and iron-gall-based inks. Additionally, SEM-BSE imaging and EDS, which provide information about the presence of vitriol and alum in some inks, support Raman spectroscopy in ink identification. Spectral imaging aids in classifying inks as either carbon-based or iron-gall-based. FTIR spectroscopy produces reliable results for ink identification, although it cannot fully differentiate between iron-gall and carbo-gall-vitriol inks. However, these two inks can still be identified due to distinct reflective spectra. Overall, this research demonstrates that combining spectroscopic and spectral imaging techniques with a multi-analytical approach is effective in identifying various types of traditional black inks.

Mirzanli, Ummugulsum, Pelin Guzel, and Nuriye Akbay. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 326 (2025): 125167.

This study presents a methodology for detecting falsified documents using a combination of spectroscopic techniques and chemometrics.

UV–Vis and FTIR-ATR spectroscopies, along with principal component analysis, were applied to analyze black, blue, and red ballpoint inks from three different brands. The results from the spectroscopic techniques were consistent across the eleven ink samples, with FTIR-ATR spectroscopy showing superior discriminative power. A novel sample preparation technique for small quantities was developed, which enhanced the sensitivity of FTIR-ATR. Statistical analysis indicated that UV–Vis spectroscopy was effective in distinguishing inks based on color, while FTIR-ATR spectroscopy was particularly useful for identifying ink brands. Further analysis of sub-brands of black inks and falsified check samples confirmed the potential of this methodology for forensic ink classification. Due to sample limitations in real-world cases, only FTIR-ATR analysis was conducted, demonstrating that document forgery could be detected even from small samples.