Forensic discrimination of blue fountain pen inks based on dielectric constant property

The present work aims to show the analysis and comparison of fountain pen inks that are crucial in forensic questioned document examination, particularly in developing nations where the likelihood of fraud is higher in situations involving checks, marriage papers, birth and death records, and similar documents via using dielectric properties of material. Dielectric constant measurement is a new and deep method for discriminating fountain pen inks. To achieve this goal the dielectric constant of the identification of fountain pen ink has been studied to differentiate commercially used blue colour fountain pen inks in Turkey. The data was obtained by designing and setting up an alternating current (AC), Function Generator, and Oscilloscope to measure the resistance of each fountain pen ink sample. The measurements were performed in the frequency range between 1 Hz and 3 MHz at room temperature. Then, resistance measurements were used to calculate the dielectric constant. To support the result, as a conventional method, TLC-IA (image analysis) was applied to the same samples to discriminate these samples based on the intensity profile of red, green, and blue (RGB) by using the software PyCharm Community 2024.1.1. The results from each method supported each other. The distinction between samples can be made based on their dielectric constants in the frequency range of 2–2.5 MHz, and their loss factors in the range of 0–1 MHz have also been found to be distinguishing variables. Also, for the result of TLC-IA similarity ratios, the mean was calculated as 51.72% while the minimum value was 9.66%. For example, Sample 6 was distinguished from other samples with these two methods. So, dielectric properties, the new method, allowed us to identify the different fountain pen inks with the obtained results.