Quantitative X-Ray Fluorescence Imaging to Evaluate the Efficacy of Micro-Structured Cellulose Foams and Poultices in Wall Painting Desalination

The crystallization of soluble salts poses a significant challenge to mural painting conservation. While cellulose poultices are widely used to desalinate mural paintings due to their high absorption and ease of handling, their effectiveness within the porous network of wall paintings remains a complex issue. For the first time, this study explores the potential of micro-structured cellulose-based foams as an alternative to conventional poultices for desalinating fresco wall paintings. A laboratory experiment compared the efficacy of foams and poultices, using fresco wall painting mock-ups (produced with the Roman technique) that were vacuum-impregnated with salt solutions (chlorides, sulfates, and mixtures). Short and long application times were considered, and foam reusability across multiple application cycles was assessed. Micro-energy dispersive X-ray fluorescence (µ-EDXRF) imaging was employed to quantitatively evaluate salt content reduction, both superficially and throughout the mock-up stratigraphy. Results show that foams are considerably more effective than poultices, achieving a salt removal efficiency between 6 and 10 times higher. The uniform micro-porous foam network enables faster desalination, reducing treatment risks and minimizing waste while supporting circular economy principles. This study also demonstrates the utility of µ-EDXRF imaging in monitoring desalination efficacy for both surface and cross-section analyses when assessing new desalination protocols.