This Rock Art in China Has Remained Bright Red for Nearly 2,000 Years. How? The Secret Ingredient Might Be Blood

A new study offers clues about how the Luoyue people created rock paintings in what’s now southern China. The murals have somehow been durable enough to withstand rain, heat, wind and humidity for centuries

Sarah Kuta | Daily Correspondent

August 25, 2026 10:00 a.m.

Share

Copy linkEmailSMSFacebookXRedditLinkedInBlueskyPrint

Add as preferred source

For nearly 2,000 years, vivid red rock art has adorned the karst limestone cliffs of southern China, depicting drums, bells, weapons, animals and human figures. Despite being regularly blasted by wind, rain, heat and humidity, many of the ruby murals have survived largely intact for centuries—a feat that has long puzzled scientists.

Now, a team of researchers says it may have uncovered the secret behind the rock art’s durability. A study that will be published in the September issue of the Journal of Archaeological Science suggests blood—possibly including blood collected during human childbirth—was a key ingredient in the paint used to create the enduring images.

The paintings, known collectively as the Zuojiang Huashan Rock Art Cultural Landscape, are in China’s Zuojiang River Valley, near the country’s border with Vietnam. They’re spread across more than 80 sites spanning roughly 160 miles.

Archaeologists suspect the art was created between the fifth century B.C.E. and the second century C.E. by the Luoyue people, a women-led fisher-hunter-gatherer society that practiced matrilineality, a system in which descent and property are traced through the mother’s side of the family.

To figure out how the art gallery has survived so long in such harsh environmental conditions, researchers collected and analyzed five fallen fragments of the paintings from three sites. The team used several techniques to analyze the samples, including how they interact with infrared light, their appearance under a high-powered microscope and their protein makeup.

Analyses hinted that the Luoyue artists created their long-lasting rock art in two steps. First, they gathered animal bones or bird droppings, as well as limestone or shells. They heated these materials to produce a mixture of calcium phosphate and quicklime, then streamed in enough water and blood to create a “milky emulsion of mortar,” the researchers write in the paper.

They used this mortar emulsion as a primer of sorts, painting a base layer directly onto the limestone cliffs. Once this layer had partially dried, they painted over it with a pigment solution made from water and local red clay rich in iron oxide. As the slaked lime reacted with carbon dioxide in the air, the blood proteins helped form calcium carbonate, securing the pigment to the rock.

“The pigments are so firmly bonded to the bedrock that when peeling occurs, it is the limestone layer itself that detaches along with the pigments,” lead author Meng Wu, a chemist at Shandong University in China, tells Science’s Soumya Sagar.

The Luoyue’s mortar created such a strong bond with the limestone that, hundreds of years later, researchers had to use an electric drill to separate the paint layers from the base rock, they write in the paper. By contrast, the rock’s natural sediments, without any paint, were only weakly bonded to the surface.

A closer look at the blood revealed that around 97 percent of the detected proteins in samples from one site came from humans. The rest came from cows, antelopes, sheep, goats or other herbivores. A sample from a different site contained roughly equal amounts of human and animal blood proteins.

What’s more, the human blood contained prolactin-inducible protein and lactotransferrin—two proteins found in high concentrations in the blood of pregnant women. The researchers suspect the blood may have been collected during or after childbirth in a nod to the matriarchal society’s reverence for women and fertility. The artists wouldn’t have needed much blood, only around eight millimeters for every square meter of rock they hoped to paint, the team estimates.

This childbirth blood idea seems to be supported by the rock art itself, which depicts pregnant women, sexual intercourse between men and women, and men with prominently featured genitalia.

“It is an extremely elegant and comprehensive study,” Matthew Collins, an archaeologist at the University of Cambridge in England who was not involved with the research, tells Science. However, because the signals of human blood were faint and didn’t seem affected by millennia in a harsh environment, he suspects the team’s samples may have been contaminated in the laboratory. The authors “may be right, but they may have overinterpreted their data.”

Jose Miguel Perez-Gomez, an archaeologist at Simon Bolivar University in Venezuela who was also not involved with the study, tells the Art Newspaper’s Hadani Ditmars that prolactin-inducible protein and lactotransferrin can also be found in people who are not pregnant, which means the blood may not have been related to childbirth. He also cautions that the study analyzed only a small number of samples and did not recover ancient DNA, making it difficult to determine whose blood was used.

Moving forward, he hopes future studies will explore whether the chemistry of the paint can shed light on the meaning and ritual significance of the rock art.

“If childbirth blood was intentionally selected, we should ask whether images associated with reproduction cluster where human blood is detected, whether pigment recipes vary according to motif and whether the spatial setting itself formed part of the ritual,” he says.

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.