LEI Yong 雷勇
The Palace Museum 故宮博物院
Was Malachite the Most Popular Green Pigment?
Based on an investigation of recent pigment analyses of many dated caves and murals, as well as some historical records and scripts in China, the most popular green pigment for wall painting and architecture might be copper trihydroxychlorides since North Dynasty (386-581 CE) until late Qing Dynasty (1840 -1911 CE), rather than malachite. Furthermore, the synthetic technology of making bronze corrosion artificially probably began to dominate the green pigments supply in Five Dynasties (907-960 CE) or Song Dynasty (960-1279 CE).
It is well known that Blue and Green Landscape Painting ("Qing Lv Shan Shui" in Chinese) is one of the dominant Chinese landscape painting trends. It illustrates the important roles that blue and green pigments play in Chinese arts. It is also well accepted for normal Chinese artists that the most popular traditional green and blue pigments in China are malachite and azurite.
However, based on recent Chinese mural and architectural painting analytical research, copper trihydroxychlorides (Cu2(OH)3Cl) might have played a more important role rather than malachite in Chinese paintings. However, this research doesn't cover Chinese painting scroll for the difficulties of nondestructive analytical requirement.
Some Chinese historical scripts might document copper trihydroxychloride. "Salt green" or "green salt" ("Yan Lv" or "Lv Yan"in Chinese) was mentioned in both the Weishu and Suishu as one of local products of Qiuci or Persian Capital.
Based on the documents above, the imported "green salt" or "Salt green" in China might be mineral copper trihydroxychlorides. The assumption matches a recent geological discovery of some copper trihydroxychlorides both in Shanshan and Qiuci.
Some scripts of Tang Dynasty (618-907) found in Turfan mentioned the price of both Malachite and copper green (Tong Lv in Chinese).If copper green was synthetic copper trihydroxychlorides, it should be easier and cheaper to obtain than mineral malachite. But the much cheaper price of malachite in Turfan scripts provided contradictory evidence. Then, the "copper green" here should be the rare mineral copper trihydroxychloride, which had a higher price than malachite.
Wang Jinyu and Li Zuixiong's research in Duhuang and Yulin Grottos suggested the copper trihydroxychlorides were the most popular green pigment before Five or Song Dynasty. Furthermore, malachite sometimes was always found together with it. The copper trihydroxychlorides and malachite can exist together in nature geologically. Therefore, mineral copper trihydroxychlorides was the most popular green pigment from North to Five Dynasties.
It is very interesting that the most popular green pigment in Dunhuang and Yulin Grottoes was pure copper trihydroxychlorides without malachite since Five Dynasties or Song Dynasty. This evidence indicates that the synthetic technology of copper trihydroxychlorides began to be popular since Five Dynasties.
There are several documents mentioning the recipes of making copper green, especially in Song and Yuan Dynasty.
For example the recipe in Song Dynasty: Firstly, vinegar added with sodium chloride was heated on a fire for a long time; secondly, the hot vinegar was poured onto copper boards in a big copper pot; thirdly, some green powder was peeled off from the boards after 4 hours. Then repeat those steps.
Based on David Scott's research, we know the final product of those recipes is copper trihydroxychlorides rather than copper acetate, especially the treatments of heating prevented making copper acetate.
Research on a wall painting of the Yuan Dyansty (1206-1368 AD) in the Nelson-Atkins Museum of Arts has shown that the most widely used original green pigment was copper trihydroxychlorides. Another achievement of this research is that it also found tin in the green pigment, which might derived from tin bronze.
Similar unpublished research was done by conservation microscopist, Inge Fiedler. She found minor to trace amounts of both tin and lead in the green pigment of a polychrome seated Guanyin (11-13th century) in the Art Institute of Chicago.
Another large mural painting of the Yuan Dynasty, Seven Buddha Sermon Illustrations, is now preserved in the Palace Museum, Beijing. By Polarizing Microscope (PLM), I found green and spherical Cu2(OH)3Cl particles with dark sports in the centre, which are one proof of artificially making.
In addition, an unpublished research on another large mural painting of the Yuan Dynasty preserved in the Royal Ontario Museum also found copper trihydroxychlorides, but without synthetic or natural identification. In addition, the similar murals preserved in Metropolitan Museum of Art, University of Pennsylvania Museum of Archaeology and Anthropology didn't receive any pigment analyses.
I was involved in a mural painting research of several Ming Dynasty (1368-1644 AD) temples in Yong Deng, Gansu Provence. Most of the green pigments particles were found to be spherical with dark spots in the centre, which is a proof of synthetic making, too. Similar evidence was also found on architectural painting in Palace Museum, Beijing.
In summary, based on a number of artifact analyses and historical scripts, for Chinese mural and architectural painting, the most popular green pigment may be copper trihydroxychlorides rather than malachite since North Dynasty until late Qing Dynasty. Then the synthetic technology probably began to dominate the green pigments production in Five Dynasties or Song Dynasty. Bronze might be more popular than pure copper when synthesizing copper trihydroxychlorides. Therefore, the green pigments supply for historical Chinese mural making was supported by the synthetic technology of copper trihydroxychlorides in a great deal rather than the mineral malachite's exploration.