## 1 Introduction  
Identifying pigments in art is one of the most important goals in the study of cultural heritage for numerous reasons, ranging from historical research and archaeometry to adequate conservation strategies [1]. From a historical and artistic point of view, the use of specific pigments is linked to specific time periods, thus helping to date artworks, providing useful information for experts, e.g., to confirm or refute the authenticity of paintings [2]. Moreover, by studying the pigments and techniques an artist used, historians can gain insights into the artistic process and the context in which the artwork was produced. On the other hand, from a conservation and restoration standpoint, pigment identification is essential for developing effective preservation strategies. The identification of pigments enables conservators to understand how to preserve painted artworks, acknowledging their reactions to environmental factors such as light, moisture, temperature fluctuations, etc., thereby mitigating deterioration and ensuring the long-term stability of the artwork [2]. In short, the scientific study of pigments not only enhances our comprehension of art history and artistic practices but also plays a crucial role in the safeguarding of cultural heritage for future generations. There are several analytical techniques that can be used for this purpose (e.g., X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, optical and scanning electronic microscopy modalities, chromatographical techniques, etc.) [3]. However, most of them are sample-invasive, and therefore not universally appreciated [3]. Nowadays, non-destructive instruments are broadly used for the in situ characterization of materials which are often more acceptable and convenient since they respect the integrity of the artwork [3;4]. The quality and performance of the equipment available have drastically improved, leading to the possibility of obtaining more information from the objects without the need for sampling [4]. Among the different analytical approaches, Fourier transform infrared spectroscopy (FTIR) can be used to characterize both organic (e.g., binders) and inorganic materials (e.g., pigments). FTIR spectroscopy utilises infrared radiation to measure the fraction of incident light absorbed at specific wavelengths. This process generates a spectrum that represents the vibrational modes of molecular bonds, enabling the structural analysis of various materials. Each spectrum serves as a chemical fingerprint for identifying minerals and provides unique insights into their molecular structure. In addition, FTIR devices have improved in the last two decades in terms of spectral resolution and detection limit, granting their consolidation as an effective and versatile technique for the study of cultural heritage materials [5; 6; 7; 8]. FTIR can be used in transmission, Attenuated Total Reflection (ATR-FTIR) and in reflectance modality, obtaining an IR spectrum that yields valuable information [7;8]. This is because the energy of most molecular vibrations is found within the IR region, particularly the mid-infrared (MIR, from 4000 to 450 cm\({}^{-1}\)) [6]. The kind of sample available will generally determine the modality applied as follows [8]:  
1. When the IR light can pass through the sample, transmission, which usually provides high spectral resolution, is the most suitable modality. However, it is considered destructive as a pelleting procedure is usually required; the sample must be grinded and mixed with another solid, typically potassium bromide (KBr). Samples can also be examined in a diamond anvil cell by previously compressing the sample (ergo, also destructive). 2. When the IR light cannot pass completely through the sample, ATR-FTIR is the most suitable since the light only interacts with the first few microns (\(\upmu\)m) of the sample.