## 1 Introduction
Traditionally, these treatments are applied using swabs, brushes, or poutlices [13; 14], which provide limited control over solvent penetration and action. Consequently, alternative application vehicles such as gels have emerged, allowing for more controlled and localized solvent delivery, thereby reducing the risk of damage to sensitive materials. Gels retain solvents and enable slower, more gradual removal of unwanted substances. Various gel formulations exist, based on cellulose derivatives, synthetic polymers, or other materials, which can be engineered to release solvents in a controlled manner [18; 19]. Some of these materials have been studied for their application in cleaning treatments on gypsum works, such as cellulose ethers like methylcellulose and hydroxypropyl cellulose [20]. PVA-borax gels have also been shown to produce good cleaning results on surfaces as porous and hygroscopic as gypsum, such as in mural paintings on plaster mortar and polychrome tempera, which therefore have characteristics similar to those of Hispano-Muslim plaster [21]. Complex polysaccharide gels, especially agar-based gels, have also been widely studied as cleaning agents for removing overpainting and dirt from both polychromed [19] and unpolychromed plaster works [11]. Regarding all different types of gels, agar-based gels are increasingly used for the removal of surface patinas such as dust and soluble salts, with a gentle action that makes them particularly suitable for cleaning sensitive surfaces such as paintings or frescoes. Furthermore, it can be easily removed from the artwork's surface after cleaning, without leaving undesired residues. In this research, many cleaning methods known in the literature, some of which have just been described, were studied and compared. In particular, the synergistic use of very promising materials for their respective intrinsic characteristics is proposed: polyamidoamine and agar-based gels. The use of glycine-functionalized polyamidoamines (PAA) for the capture of pigments from paint layers to be removed has been studied. Being an evolving field of research, the applications of this material in the restoration of artworks and in the removal of contaminants from delicate surfaces are being explored, although the chelating abilities of PAA have already been the subject of study [22; 23]. The advantage of using PAAs lies in the possibility of creating gels with controllable properties, such as viscosity and swelling capacity. Furthermore, their chemical structure can be modified to optimize the interaction with specific materials. PAA gels act as matrices that trap pigments through chemical and physical interactions. The removal of pigments is achieved by applying the gel to the surface to be cleaned, followed by the removal of the gel that has incorporated the pigments. Finally, it can be considered that this type of treatment can be used for the selective removal of undesired pigments from paintings, frescoes, and other polychrome artifacts, carefully selecting certain areas and cleaning delicate surfaces without damaging the original paint layers. To develop appropriate cleaning treatments, it is necessary to simulate the actual ageing of this type of plasterwork. For this reason, an innovative ageing protocol was proposed to subject the samples to climatic stress conditions that can occur in the Iberian Peninsula. Possible alterations undergone by materials during ageing were evaluated, especially for organic materials that tend to denature and lose physical properties. The samples were characterized before and after artificial ageing protocol (AAP), focusing on the organic components (animal glue, Arabic gum, and linseed oil). In this way, it is possible to establish a specific protocol that simulates the evolution and deterioration that occurs in the original materials. These characterizations were carried out by colorimetric evaluation, Fourier Transform Infrared Spectroscopy (FTIR), and Gas Chromatography coupled with Mass Spectrometry (GC-MS), both original polychromy and repaintings.