Ancient paintings covering towering river cliffs in southern China have survived for at least 2,000 years despite intense heat, monsoon rains and frequent typhoons. New analysis suggests that part of the reason may be an unusual paint mixture made with lime mortar and blood.
The Huashan rock art landscape stretches for 260 kilometers (162 miles) near the border with Vietnam. Across more than 80 locations, thousands of images show people, musical instruments, boats, animals, weapons and other figures.
To investigate how the paintings were made without damaging them, researchers examined fallen fragments of rock from the base of three sites. They used scanning electron microscopy to study the individual paint layers and spectroscopy to identify their mineral and chemical composition. They also tested the samples for ancient organic binders.
The red pigment appeared to have come from local red clay containing microscopic iron oxide particles known as nano-hematite. But those pigment particles were not simply deposited on the rock. The analysis found them enclosed in the outer layer of a manufactured mortar containing lime and blood.
That finding points to a possible role for blood in helping the paint adhere to the cliff.
Blood may have strengthened the paint
The researchers propose that blood could have acted as a natural chemical hardener when mixed with lime. According to their interpretation, proteins in the blood triggered a reaction that caused calcium carbonate to form around the pigment particles.
That process may have helped bind the pigment directly to the rock surface, creating a durable composite material.
The researchers describe the result as a stable combination of organic and inorganic materials and say it reflects complex technological processes used by the artists.
The evidence also raised a possible symbolic explanation for the blood. The ancient artists belonged to the Luoyue people, described in the study as a matriarchal society. Tests detected human serum proteins, leading the researchers to suggest that the blood may have come from females who had given birth.
They propose that such blood could have carried a symbolic connection to life and renewal within the community’s worship of female fertility. This remains an interpretation of why blood was included in the paint.
The paintings required more than manpower
The Huashan paintings were already known to have required substantial physical effort. Creating images high on dangerous cliffs would have meant scaling the rock faces and transporting large amounts of paint.
The new findings suggest that the technical side of the work may have been just as important. The researchers argue that the artists were not simply carrying out a labor-intensive task but were using a technically intensive process to produce the paintings.
The study was published in the Journal of Archaeological Science.
