## 1 Introduction  
Among the important forensic procedures for the examination of questioned documents are handwriting analysis, authentication of documents, forgery detection, and ink discrimination [1, 2]. The chemical analysis of inks can reveal information about questioneddocuments based on the inorganic and organic characteristics of the writing pen ink matrices [3]. The role of pen ink analysis and the area of questioned document analysis has been significantly growing and is being addressed more in forensic chemistry [4]. Several chemical and physical techniques are used in the chemical analysis of hand-written documents quite apart from the classical mainstay of handwriting comparison. Today, the advent of modern instrumental methods of inorganic and organic analysis permits the comparison of pen inks for the sake of identification and discrimination [3; 4; 5]. A spot of typical writing pen ink is composed mainly of a colorant agent such as a dye or pigment, a vehicle including solvent and resin, and some additives such as emulsifying agents, surfactants, and anti-corrosion compounds. Ink analysis can reveal information about its chemical components and manufacture, which are valuable for ink discrimination, identification, and dating [6; 7]. The colorant agents such as dyes and pigments are the most important components of certain ink samples. BP and gel pens are amongst the most commonly used pen types, and each type has its specific chemical and physical characteristics. BP pen ink typically contains either a single dye or a mixture of two or three dyes to retain an appropriate color. Gel pen ink might contain only dyes or a mixture of dyes and pigments [8; 9]. Identifying inorganic pigments of writing pen inks and studying their optical properties such as luminescence and quenching plays a crucial role in forensic ink examination. Analytical techniques such as X-ray spectrometry, laser-ablation mass spectrometry, laser-induced breakdown spectrometry, and inductively coupled plasma mass spectrometry are employed to determine the elemental composition of inks, enabling the identification and quantification of various metallic components present in ink formulations. Optical absorption, emission, and reflectance spectrometry techniques are also vital for revealing the luminescence and quenching properties of inorganic or organic luminescent species within the ink formula [2; 10; 11]. Forensic examination of pen inks on documents relies in the first stage on non-destructive and simple tools such as visual and optical examination using microscopy and video spectral comparator (VSC) techniques [12]. Forensic examination of inks using microscopy techniques can be useful only for differentiating different types of ink and discriminating between pens of the same type that vary in mechanical features or color tones [13]. The VSC is considered the first analytical tool that is typically employed by forensic examiners for the primary examination of ink on documents. The VSC is a non-destructive technique that is fast, user-friendly, and can carry out sample-free analysis of questioned documents, and thus is one of the most common toolkits used in forensic document examination [8; 14; 15]. Infrared luminescence (IRL) and infrared reflectance (IRR) comprise highly effective approaches for ink differentiation using the VSC. They are based on discerning variances in the IRL and IRR of the questioned ink samples, whereby the inks are accordingly deemed distinguishable or indistinguishable [12]. The VSC instruments may also comprise a micro-spectrometer, enabling the measurement of reflected, transmitted, and luminescent light, which is a simple and valuable addition for the examination of a variety of pen types and documents [15]. Further forensic examination of inks using more complex and destructive analytical tools such as chromatography and spectroscopic techniques is typically required for deeper chemical analysis in forensic investigations [15; 16].