The Relation between the Fine Structural Change and Color Fading in the Natural Mineral Pigments Azurite and Malachite

Abstract

AbstractMany ancient Asian and Japanese paintings have been drawn with natural mineral pigments. The discoloring mechanism of these pigments has been a real concern for the characterization, restoration and preservation of the ancient cultural properties. The authors expect that the color fading is deeply related with the chemical composition and the fine structural change of the major elements. Therefore the purpose of this paper is to make clear the relation between the fine structural change and color fading.We analyzed several representative pigments of Japan, including copper carbonate hydroxide pigments (blue verditer and green verditer, “gunjo” and “ryokusho” called in Japanese) by x-ray fluorescence analysis (XRF) and x-ray absorption fine structure (XAFS). In order to examine the deterioration of pigments, some of them were exposed in the highly-heated condition. In addition, the spectral reflectivity data are also collected on spectrophotometer system.Here we propose to compare the results obtained from XRF and XAFS with the spectral reflectivity data. The results demonstrate that the chemical composition and the fine structural change can provide valuable information for revealing the discoloring mechanism, which would then lead to the original color estimation of the ancient cultural properties.