Influence of Taoism on the invention of the purple pigment used on the Qin terracotta warriors

Abstract

Introduction:In March 1974, Chinese farmers made a remarkable archaeological find: during the sinking of wells for farmland irrigation construction near Xi'an (Shaanxi province, China) they discovered an army consisting of more than 8000 life-size terracotta figures of warriors and horses dating from the First Emperor of the Qin dynasty, Shi Huang Di (reigned ca 221 BC -ca 210 BC). The figures, facing east and ready for battle, were individually modelled with their own personal characteristics, and were accompanied by their weapons, real chariots, and objects of jade and bone. How, more than 2000 years ago, the ancient Chinese constructed these large and heavy statues and what technologies they used to finish such a large project are questions which are still only partially answered by modern archaeologists.The discovery that BaCuSi 2 O 6 (FitzHugh and Zycherman 1983, FitzHugh and Zycherman 1992), also known as "Chinese Purple", was the main constituent of the purple pigment used in the paint covering the warriors constitutes an enigma in itself.This pigment was also used later in the Han dynasty in pottery (hence its other common name of "Han Purple") and for trading. BaCuSi 2 O 6 is a mineral that has never been found in nature, which implies that the makers of the warriors must have been able to synthesize it. The process to synthesize BaCuSi 2 O 6 is now known to be highly complex ). An additional problem with the Egyptian-Chinese connection theory is that, to our knowledge, no Ca-bearing Egyptian Blue has been found in China. 4 In order to address these questions, we re-examined the chemistry and the morphology of purple pigments found on one of the Qin Terracotta warriors ( fig. 1). By combining our findings of the technology used in the synthesis of Chinese Purple with existing archaeological evidence, we conclude that Taoist alchemists invented this pigment as well as the related pigment Chinese Blue independently from any Egyptian influence. Experimental Methods:Our investigation was based on a two pronged approach. We used a small fraction of our specimen, ground it into fine powder and used synchrotron radiation high-resolution powder x-ray diffraction (XRD) analysis to identify the crystallographic phases present. Then based on this inventory, we used spatially resolved x-ray and electron micro-beam techniques, such as micro X-ray diffraction (µXRD), micro X-ray fluorescence (µXRF) and Scanning Electron Microscopy (SEM) based Energy Dispersive X-ray (EDX) microanalysis, to study the chemistry of individual pigment clumps and map the distribution of these and other minority phases in the pigment.These chemical and phase maps gave us an insight into how the pigment was synthesized.Synchrotron radiation is 8-12 orders of magnitude more brilliant than the high performance rotating anode x-ray tubes (Eisenberger 1986). The X-ray beams at current third generation synchrotron radiation sources can be focused to a one micrometer size spot and still maintain high photon fluxes (>10 10 ph/s/µm 2 ) to ob...

Synchrotron Methods: Color in Paints and Minerals

“…Purple pigments such as Co, Mn, and ultramarine violet only became available by synthesis from the mid-nineteenth century. Chinese purple samples have been submitted to highresolution SR-XRD to identify the crystalline phases and additionally to a combination of micro-XRD/XRF (at ALS, beamline 7.3.3, Lawrence Berkeley National Laboratory (LBNL), and beamline 6-2 at SSRL) and SEM-EDX allowing the acquisition of chemical and phase maps of the heterogeneous pigment (Liu et al, 2007). This pigment was also found as a main component on the purple paints of the Qin terracotta warriors of the First Emperor of the Qin dynasty (221-210 BC; Liu et al, 2007).…”

“…It is therefore remarkable that in a limited period of the Han dynasty in China (208 BC-AD 220) and some centuries before, a purple pigment, a BaCu silicate with the chemical formula BaCuSi 2 O 6 called also Han purple, often in association with a synthetic blue pigment BaCuSi 4 O 10 , was identified (West Fitzhugh and Zycherman, 1992). Motivations to imitate jade diminished and consequently the use of BaO in glass production that led to the pigment manufacturing (Liu et al, 2007). The process of manufacturing Chinese purple is highly complex.…”

Diffusion Of Indigo Molecules Inside The Palygorskite Clay Channels

“…The first known artificial pigment is the Egyptian Blue 1 (2 nd millennium BC). Chinese also elaborate a blue/purple pigment found on pottery 2,3 and the terra cotta soldiers of the First Emperor of Qin 4 . Production of Maya Blue in the pre-Colombian MesoAmerica constitutes another example of the know-how of the ancient people 5,6 .…”

Scientific investigation of the paint and adhesive materials used in the Western Han dynasty polychromy terracotta army, Qingzhou, China

“…Han purple and Han blue are synthetic barium copper silicate pigments that were developed in China at least 2000 years ago. It is known that those pigments were in use by the late Western Zhou dynasty (800 BCE) until the end of the Han dynasty (Liu et al, 2007). Those pigments were found in artifacts of beads, earrings, and octagonal sticks, as well as in paint layers of the terracotta army from the Qin dynasty (221e207 BCE) and on wall paintings of Han dynasty tombs (206 BCEe220 CE) (Heinz et al, 2010).…”