Investigations with Dibasic Esters: A Green Approach to Varnish Removal from Oil Paintings

Removing altered varnishes and retouching from oil paintings is a delicate and irreversible procedure in the conservation of cultural heritage. Surfactant-free gelled o/w emulsions containing dibasic esters (DBE) provide a green, safe, and environmentally friendly alternative to traditional solvent methods. The use of Xanthan gum and polyacrylate as thickening agents successfully restricted solvent diffusion, thereby minimizing the risk of interaction with water-sensitive substrates. Spectroscopic and microscopic analyses (FTIR and SEM) were employed to evaluate the cleaning efficacy and to assess the morphological integrity of the paint surface post-treatment, detecting potential inhomogeneities, erosion, or pigment loss. Determination of surface conductivity has allowed us to verify the degree of removal of any residues that could have undesirable long-term effects. Fatty acid leaching was quantified by gas chromatography-mass spectrometry (GC/MS): the use of free DBE resulted in a loss of up to 60% of the lipid component, while for surfactant-free gelled o/w emulsions with DBE, this figure was significantly reduced, with no observable surface damage. The tests were performed at both neutral pH and pH 8.5. The pH change was consistent with expected values: alkaline and ionizing conditions enhanced the emulsifying and removal effect, as well as the interaction with the painting medium. These results suggest that surfactant-free gelled o/w emulsions represent a promising alternative to conventional solvent-based systems, offering effective varnish removal while minimizing risks to both artifacts and restorers.