Characterization of Thai Mural Paintings from Mid to Late Ayutthaya Period (1488-1688) on the case studies of Wat Chaiwatthanaram, Wat Chong Nonsi and Residential Building of Somdet Phra Phutthakosajarn ​

Thailand's Cultural Heritage faces significant challenges in preserving traditional mural paintings, given their historical and artistic importance. To ensure effective conservation, it is crucial to investigate the sources, categories, properties, and degradation processes of these materials over time, as well as the underlying causes and mechanisms of their alterations. This understanding is essential for selecting compatible materials and appropriate conservation methods, in alignment with international standards for heritage preservation. The present study focuses on the characterization of Thai pigments and binders used in secco techniques, as well as the environmental factors contributing to the degradation of murals from the Mid to Late Ayutthaya period (1448–1688). Specific sites under investigation include Wat Chaiwatthanaram (UNESCO site) and the residential building of Somdet Phra Phutthakosajarn in Ayutthaya, and Wat Chong Nonsi in Bangkok. These sites represent unique forms of ancient Thai artistic heritage, revered for their beauty and mysticism. A main aim of this work is the identification of key pigments—such as black, green, and red—which were fundamental to the Ayutthaya period's color palette. To this purpose, as a first step, non-invasive investigations with a colorimeter were carried out on site, and collected colorimetric data were analyzed to have a first overview of the possible pigments. As a second step, small fragments taken from the sites were analyzed with a range of advanced techniques, including Optical Microscopy, Micro-Raman Spectroscopy, Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy (SEM-EDS), Micro-Fourier-Transform Infrared (microFTIR) spectroscopy and Electron Paramagnetic Resonance (EPR). Additionally, the study examined the mortar used as the ground layer in Wat Chaiwatthanaram. This research is complemented by documentary studies and qualitative fieldwork, which includes interviews with conservators and restorers involved in safeguarding Thailand’s Cultural Heritage. While the study is limited to samples from selected sites, the findings will contribute to an evidence-based understanding of the materials used in 16th-century Thai mural painting. The knowledge gained highlights the adaptive strategies employed by artisans in a humid climate, characterized by heavy rainfall, river basins, and annual flooding. Additionally, the study reflects the impact of present-day environmental changes on heritage buildings. In summary, this study offers valuable insights into the preparation of local Thai materials used in historical paintings, while also contributing to the improved management and protection of cultural heritage. The findings aim to ensure the preservation of Thailand’s artistic legacy, safeguarding its intrinsic values for future generations.