Color Properties of Natural Ultramarine Pigments with the Effect of Preparation Processes and Raw Rock Quality

Abstract

Natural ultramarine is a traditional and expensive blue pigment widely used around the world. It has been found recently in the decorative paintings (caihua 彩畫) of historical Chinese buildings. Interestingly, the preparation and application methods for this pigment have not been documented in Chinese painting reviews and artisans’ manuscripts before the 20th century. The sedimentation method (also named “Shuifei 水飛”) was likely the approach used by Chinese artists and craftsmen to produce this blue pigment. The extraction method (recorded by Cennino Cennini) was another representative method. Both methods have been used to prepare this blue pigment. Through the experiments of pigment and color sample, 21 natural ultramarine pigments produced by these two methods were collected. By means of color measurement and polarized light microscopy, this study aimed not only to summarize the color properties of this pigment mixed with gelatin but also to try to reveal how preparation process and raw rock quality influence its color effect. The colorimetry study of natural ultramarine pigments will provide data and visual references for heritage conservation and restoration, as well as traditional color design. Analyzing the pigment’s color properties from the perspective of materials and techniques will help uncover the intentions behind its history.