Hidden Technologies of Thai Gold Glass Mirrors: Interface Chemistry and Raw Material Signatures Across Thailand

This study identifies the technological signature of ancient and alternative “Chu” and “Kriab” gold glass mosaic mirrors from Thailand. Although these mirrors play an important role in Thai decorative heritage, their production routes and interfacial chemistry at the lead-to-glass interface have remained unclear. A survey of 154 sites across Thailand shows mosaic glass was widely distributed and likely produced during the Ayutthaya period (~300 years ago). PXRF, WD-XRF, SEM, and XPS were used to examine the material properties of observed Chu mirrors. Most samples can be classified as a mixed lead-alkaline glass type, with PbO content ranging from 4.28 to 48.17 wt%. Their yellow tone is controlled by iron and manganese redox states. Chemical and physical analyses distinguish between Chu1 and BKK[7], which share a silica source but rely on different flux, pointing to different glass workshops. Additionally, some Chu and Kriab samples exhibit evidence of potential use of recycled materials. Depth profiling showed that there were lead species at the interface, including PbO4, PbO, and Pb0. The ancient samples had higher Pb0 concentration due to reducing kiln conditions. Silanol groups on the glass surface are identified as the key factor promoting the adhesion of lead coating to the glass surface. Variations in raw materials and coating techniques further differentiate ancient Chu mirrors from modern reproductions. This research offers useful information about the technological ingenuity of ancient artisans and supports the conservation and replication of these culturally significant artifacts. The results contribute to preserving Thailand’s rich heritage in decorative glasswork and lay a foundation for future research into material provenance and historical restoration practices.