Blood May Help Explain China’s Enduring Red Cliff Paintings

Across more than 80 sites in southern China’s Zuojiang River Valley, vivid red paintings show drums, bells, weapons, animals and human figures on limestone cliffs. Despite centuries of wind, rain, heat and humidity, many remain remarkably well preserved. A study scheduled for publication in the September issue of the Journal of Archaeological Science suggests that blood may have helped make the images so durable. The paintings, known as the Zuojiang Huashan Rock Art Cultural Landscape, are generally believed to have been created between the fifth century B.C.E. and the second century C.E. by the Luoyue, a matrilineal fisher-hunter-gatherer society. Researchers analyzed five fallen fragments from three locations using infrared techniques, high-powered microscopy and protein analysis. Their proposed reconstruction is that the artists first made a mortar from heated animal bones or bird droppings combined with limestone or shells. Water and blood were then added, producing a milky mixture that was applied to the cliff as a base layer. After the layer partly dried, the artists covered it with a solution made from water and red clay containing iron oxide. According to the researchers, a reaction involving lime, carbon dioxide and blood proteins helped form calcium carbonate, firmly attaching the pigment to the limestone. The team says the bond was so strong that, centuries later, an electric drill was needed to separate painted layers from the underlying rock. Protein analysis at one site indicated that about 97 percent of the detected blood proteins were human. A second site showed approximately equal amounts of human and animal blood proteins. The researchers also identified two proteins associated with blood from pregnant women and proposed that blood collected during or after childbirth may have reflected the Luoyue’s emphasis on women and fertility. The art includes pregnant women, sexual scenes and men with prominently depicted genitals. That interpretation remains uncertain. Matthew Collins, an archaeologist at the University of Cambridge who was not involved in the research, said the human-blood signals were faint and may have resulted from laboratory contamination. Another outside archaeologist noted that the identified proteins can also occur in people who are not pregnant. The study examined only a small number of samples and did not recover ancient DNA, leaving the source and possible ritual meaning of the blood unresolved.