Characterization and quantitation study of ancient lacquer objects by NIR spectroscopy and THM-Py-GC/MS

Abstract

Abstract Oils were often used as additives in lacquering process in ancient time, and the proportion of oil to lacquer is crucial for the quality of the lacquer objects. In order to quantitative analyze the proportion of oil to lacquer in the ancient lacquer objects, Near-infrared spectroscopy (NIRS), a non-destructive method was studied. In this research, a partial least squares (PLS) model of reference samples for quantitative analysis of lacquer films was established. When evaluating the final model, factors such as correlation coefficient (R) and the root mean square error of prediction (RMSEP) were considered. The final optimal results of the PLS model showed that RMSEP and correlation coefficients (R) in the calibration set were 0.112 and above 0.98, respectively, demonstrating that NIRS can be used to the quantification analysis of lacquer film. Subsequently the developed PLS model was applied to quantitatively analyze the lacquer samples from the Buddhist statue and altar of Qing dynasty, while thermally assisted hydrolysis–methylation for pyrolysis-gas chromatography-mass spectrometry (THM-Py-GC/MS) was applied for the qualitative analysis. The results show that urushiol-based lacquer and tung oil were used and the ratios of oil in lacquer are varied in different objects for special purposes. For the first time, the proportions of oil to lacquer were revealed in the ancient lacquer objects, which is significant to enhance the knowledge about lacquering techniques in ancient times.