A Methodology for Lacquer Gilding Restoration of Sandstone Sculptures: A Multidisciplinary Approach Combining Material Characterization and Environmental Adaptation

Abstract

The restoration of gold leaf on sandstone sculptures requires structural stability, aesthetic considerations, and compliance with the principles of cultural heritage preservation. A primary issue is achieving visual and material compatibility between newly restored and original areas. Based on the “Diagnosis–Analysis–Selection–Restoration” methodology, the research team developed a targeted restoration approach for gilded stone sculptures, using the Shakyamuni sculpture at Erfo Temple in Chongqing as a case study. Assessment of the current situation revealed that over 70% of the sculpture’s surface exhibited gold leaf delamination. The composition and structure of the gold-sizing lacquer, lacquer plaster filler, ground layers, and pigments were investigated using SEM-EDS, XRD, Raman spectroscopy, and THM-Py-GC/MS techniques. The results confirmed that the sculpture featured a typical multilayer gilding structure with clear evidence of historical restorations. Considering both material performance and interfacial compatibility, an NHL2/SiO2/SF016 composite emulsion and traditional lacquer plaster were selected as the optimal materials for reattachment and infill, respectively. A scientific restoration protocol was developed, encompassing gentle cleaning, targeted reattachment and reinforcement, and region-specific repair methods. Principal Component Analysis (PCA) was used to evaluate the influence of temperature and humidity on the curing behavior of lacquer layers. Additionally, a non-invasive gold leaf color-matching technique was developed by controlling the surface roughness of the gold-sizing lacquer, effectively avoiding the damage caused by traditional color-matching methods.