Green Solvent-Based Gel Cleaning Systems for the Selective Removal of Aged Synthetic Resin from Mural Paintings: A Multi-Analytical Evaluation for Sustainable Conservation

Sustainable conservation of cultural heritage encompasses not only the use of environmentally friendly materials but also minimizing the impact of conservation treatments on the cultural heritage object through the selection of treatment methods based on scientific evidence to ensure its long-term preservation. Aged synthetic resin applied to earthen mural paintings can increase surface gloss, form resin films, and promote contaminant accumulation, requiring cleaning treatments that balance resin reduction with the preservation of the original paint layer. This study evaluated the applicability of green solvent-based gel cleaning systems using mock-up samples prepared to reproduce the deterioration patterns of Paraloid B-72 identified on the Mural Painting in Josadang Shrine of Buseoksa Temple, a National Treasure of Korea. Cleaning performance was comprehensively assessed through morphological, optical, and chemical analyses using optical microscopy, spectrophotometry, hypercolorimetric multispectral imaging (HMI), external reflection Fourier transform infrared spectroscopy (ER-FTIR), and scanning electron microscopy (SEM). The cleaning behavior was governed by the combined effects of gel matrix, resin-film thickness, solvent composition, and gel application time. Under the tested mock-up conditions, the Nevek-based gel system achieved the most favorable balance between selective resin reduction and paint-layer preservation. Multi-analytical evaluation further demonstrated that visually favorable cleaning results did not necessarily indicate complete resin removal. These findings provide a scientific basis for evidence-based conservation decision-making and support a more sustainable, minimum-intervention approach to the conservation of earthen mural cultural heritage.