Blended Thitsiol/Urushiol Asian laquers in Cultural Heritage: curing, ageing, and photo-aging study by THM-GC/MS and other techniques

Nowadays Western Museums host a variety of precious collection of Asian Lacquers dated since the XV century, exported from Eastern Asia to a West fascinated by exotic objects and furniture. The focus of this research is a blend of two Asian Lacquer types, thitsi and urushi, very common in the West collections due to its cheap price. This special material has been studied for two years, starting from its curing process to the final artificial photo-aging. In order to acquire a deep knowledge of the chemical structure and its degradation process, both chemical and physical approach have been adopted. THM-Py-GC/MS has been used to determine the structures of the blend in comparison with the two pure lacquers, thitsi and urushi, through their typical markers, such as alkyl benzenes and aliphatic hydrocarbons, and oxidation products, such as substituted dimethoxybenzenes and mazzeic acid, and their oxidative reactions after UV exposure. THM-Py-GC/MS was joined by both ATR- and Transmission FTIR techniques, which were used to monitor the changes in the principal and characteristic functional groups of the lacquers, in a destructive (THM-Py-GC/MS) and non-destructive (FTIR) way. In conclusion, these data have been used to explain the images obtained with Digital Microscope during the whole research, in which it is clearly possible to see micro-cracks on the surface of thitsi and the blended lacquer but not of urushi, providing an overview of what kind of reactions could happen during the time, their mechanisms, why they happen and how to prevent them.