## 1 Introduction  
The conservation of cultural heritage requires meticulous approaches to preserving artworks, often relying on organic solvents for various restoration and maintenance tasks. Most of the solvents used, while effective, have raised concerns regarding their environmental impact and adverse health effects on conservators [1, 2]. Today it has become imperative to commit to sustainable conservation practices, in line with global initiatives such as the EU Green Deal and Agenda 2030. Organic solvents play a multifaceted role in cultural heritage conservation, from surface cleaning and protective coating to adhesive dilution and organic matter removal [3, 4, 5, 6, 7]. An unresolved challenge in this domain pertains to the removal of substances exhibiting low polarity or non-polar characteristics [8, 9]. Solvents commonly used for their removal [10, 11] pose considerable environmental and health risks, particularly in the case of material such as microcrystalline waves, which are widely employed as protective coatings for the substrate of diverse artworks [12; 13; 14; 15; 16; 17]. In response to the escalating demand for sustainable practices, various new strategies for removing low/non-polar substances have been studied [18; 19; 20; 21]. Recently, fatty acid methyl esters (FAME) are being studied as a potential green solvent. These compounds have emerged as promising candidates to replace low-polarity solvents due to their biodegradability, minimal volatile organic compound (VOC) emission, and non-toxic nature [22; 23]. Synthesized through alkali-catalysed reactions involving fats and methanol [24], the fatty acid chains comprise carbon chain lengths ranging from C6 (e.g., methyl hexanoate, CAS 106-70-7) to C18 (e.g., methyl stearate, CAS 112-61-8), mainly saturated but also mono- and di-unsaturated C18 (e.g., methyl oleate, CAS 112-62-9 and methyl linoleate, CAS 112 63 0). The present study endeavours to explore the potential of FAME as an alternative solvent for removing low-polarity materials commonly used as in-painting media and picture varnishes like low molecular weight (LMW) synthetic resins (Regalrez 1094) and microcrystalline wax [25; 26]. The aim of the experiment was to evaluate the effectiveness of FAME in removing the aforementioned low-polar substances. FAME were applied to the surface of prepared laboratory mock-ups (four canvases coated with two different types of non-polar coatings: microcrystalline wax and Regalrez 1094 varnish) using a gel formulation due to their negligible or low volatility, thus addressing the need to prevent solvent-substrate interactions in cultural heritage applications. The cleaning efficacy was assessed on the laboratory samples utilizing the following analytical techniques: visible (vis) and ultraviolet (UV) imaging, digital microscope observations, spectrocolorimetry, Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). In cleaning restoration practice, an important step (and the first that should be carried out) is the evaluation and choice of the most suitable solvent in order to assess different parameters;namely, assessing compatibility with the artwork's constituent materials, finding the solvent with the most suitable strength to remove the substances in question, and avoiding unwanted solvent-substrate interactions. The prevalent tool among conservators for solvent evaluation and identification of potential eco-friendly alternatives is the Teas Chart [27]. Although the Teas Chart is characterized by several limitations pertaining to solute-solvent interaction phenomena like leaching and swelling and by its inability to address substance solubility under varying pH conditions [28], for the conservator, it represents an invaluable resource. The solvent power is described on a triangular graphic using the three Hansen solubility parameters (5d: dispersion forces; 8p: polar forces; and 8h: hydrogen bonding). According to the Teas Chart, the area for wax (non-polar material) is located at the lower right corner.