Human blood may have helped preserve China’s 2,000-year-old rock art

On the limestone cliffs above China’s Zuo River, thousands of red human figures, animals and objects have faced heat, rain and monsoonal moisture for around 2,000 years. A Shandong University-led analysis now points to an unsettling ingredient in the paint: components of human blood.

The paintings form the UNESCO-protected Zuojiang Huashan Rock Art Cultural Landscape, a vast gallery linked by archaeologists to the Lạc Việt, or Luoyue, cultures that lived near today’s China–Vietnam border until roughly 100 CE. Radiocarbon dating indicates that some of the earliest images could be nearly 2,400 years old.

To understand how the paint was made, researchers examined fallen rock fragments from three sites. Several tests used different wavelengths of light to identify chemical signatures, while another method broke proteins into fragments and mapped the organic materials present. The red color appears to come from clay rich in iron oxide particles, or haematite.

The likely binder was a mortar made from slaked lime — calcium hydroxide — and blood. The study indicates that only a small amount may have been needed, with blood from humans and at least two herbivorous animal species. Researchers suggest the material could have been collected during births, a possible fertility symbol in a society led by women. Blood-based binders are not unknown in ancient painting, but the finding helps explain how this exposed artwork remained so bright.

So what does it change, concretely? It offers a possible explanation for the paintings’ durability and provides another clue to the techniques used by their creators. It also adds a biological clue to the meaning of the ritual material. The analysis does not yet answer why artists climbed so high or what the images represented, and future studies could shed more light on the history of the artworks.