Innovative gels for the removal of unwanted layers from painted artifacts

Water-based detergent systems, such as nanostructured fluids, offer several advantages, over organic solvents, for the cleaning of Cultural Heritage artifacts in terms of selectivity and gentle removal of grime materials or aged polymers, which are known to alter the readability of the painting. Unfortunately, most of the painted artifacts are water-sensitive, so using water-based systems might favor mechanical stresses between substrate and paint layers, which could lead to the detachment of pictorial layers. In order to avoid artifacts damage and to ensure a fine liquid diffusion control (layer by layer) for the removal of unwanted layers, water-based cleaning systems have been confined into innovative chemical hydrogels, specifically designed for cleaning water-sensitive Cultural Heritage artifacts. The synthesized hydrogels are based on semi-interpenetrating chemical poly(2-hydroxyethyl methacrylate)/poly(vinylpyrrolidone) networks with suitable hydrophilicity, water retention properties, and required mechanical strength to avoid gel residues after the cleaning treatment. Three selected hydrogel systems were investigated when loaded with water and with nanostructured fluids. Water retention and release properties were studied by quantifying the amount of free and bound water through Thermoanalysis; microporosity was obtained from Scanning Electron Microscopy; hydrogelʼs mechanical properties from Dynamic Mechanical Analysis; gel networkʼs structure from Small Angle X-ray Scattering. To demonstrate both the efficiency and versatility of the selected hydrogels in confining and modulating the cleaning agentʼs action, several mock-ups were tested and two important case-studies were addressed: the removal of overpaintings from the contemporary mural painting of modern artist Giuseppe Capogrossi and the removal of grime and aged adhesives from an important Vincenzo Coronelliʼs Terrestrial Globe.