Polymeric materials have been used by painting conservator-restorers as consolidants and/or varnishes for wall paintings. The application of these materials is carried out when confronting loose paint layers or as a protective coating. However, these materials deteriorate and cause physiochemical alterations to the treated surface. In the past, the monumental neo-gothic wall painting ‘The Last Judgment’ in the chapel of Sint-Jan Berchmanscollege in Antwerp, Belgium was treated with a synthetic polymeric material. This varnish deteriorated significantly and turned brown, obscuring the paint layers. Given also that the varnish was applied to some parts of the wall painting and did not cover the entire surface, it was necessary to remove it in order to restore the original appearance of the wall painting. Previous attempts carried out by conservator-restorers made use of traditional cleaning methods, which led to damage of the fragile paint layers. Therefore, gel cleaning was proposed as a less invasive and more controllable method for gently softening and removing the varnish. The work started by identifying the paint stratigraphy and the deteriorated varnish via optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy. A polyvinyl alcohol–borax/agarose (PVA–B/AG) hydrogel loaded with a number of solvents/solvent mixtures was employed in a series of tests to select the most suitable hydrogel composite. By means of the hydrogel composite loaded with 10% propylene carbonate, it was possible to safely remove the brown varnish layer. The results were verified by visual examinations (under visible light ‘VIS’ and ultraviolet light ‘UV’) as well as OM and FTIR spectroscopy.

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Alizarin (1,2-dihydroxyanthraquinone) forms coloured coordination complexes with metal ions; however, the molecular structure and formation mechanisms of aluminium-based lake pigments remain incompletely defined. In this work, Fourier Transform Infrared (FTIR) spectroscopy was employed to investigate the coordination environment and phase composition of alizarin-aluminium pigments synthesised via two distinct approaches: an alkaline complexation route and an acid-mediated precipitation route. Within each method, pH was systematically varied to evaluate its influence on complex formation and precipitation processes. FTIR spectra display significant modifications in the carbonyl and phenolic stretching regions, reflecting changes in alizarin deprotonation and metal-ligand coordination modes as a function of synthesis pathway. Shifts in ν(CO) and ν(CO) bands, together with variations in band profiles, indicate differences in binding geometry and degree of complexation. The synthetic route markedly affects nucleation and precipitation behaviour, altering the relative contributions of coordinated alizarin species and amorphous Al(OH)₃ substrate. Furthermore, pH governs ligand deprotonation equilibria and co-precipitation processes, ultimately determining pigment composition and structural homogeneity. These findings highlight the critical importance of each synthesis stage in directing coordination structure, phase development, and ultimately the properties of the resulting lake pigments.