Precise in-situ detection of inorganic pigments in ancient architectural color paintings by HH-XRF

Abstract

Abstract The handheld X-ray fluorescence spectrometer (HH-XRF) is commonly used to detect the inorganic elemental composition of pigments on-site. However, the accuracy of in-situ detection results can be affected by the characteristics of the painted surface contaminants and the layered structure of pigments in ancient architectural color paintings. To mitigate this error, a method was proposed that combined the XRF spectra of inorganic pigments with the elemental concentration values obtained through principal component analysis (PCA). Additionally, this study discussed the typical surface contaminants and pigment layering found in color paintings separately. Firstly, experiments were conducted on dust accumulation layers of varying thicknesses. The results indicated that the condition of color paintings after pretreatment of dust accumulation tended to resemble the situation with thin dust accumulation during in-situ testing. A fitting formula was derived to establish a relationship between field testing and laboratory testing results. Secondly, experiments were conducted using various combinations of pigment layers. Based on the findings, it was hypothesized that there was a connection between XRF detection results and the maximum concentration value of a single element (as determined by XRF, in an unmixed or unlayered pigment sample without dust or smoke accumulation). The test results were fitted using a Polynomial formula, providing evidence for the existence of a nonlinear functional relationship between these two variables. Finally, an empirical formula for predicting the concentration values of the top color layer with different base colors was proposed. This study offered a precise method for accurately assessing pigments of ancient architectural color paintings through in-situ testing.