How did the Huashan rock art survive for roughly 2,000 years on limestone cliffs exposed to monsoon rain? A new study points to an unusual material answer: red-clay pigment bonded to the rock with a lime mortar that appears to have included blood proteins.
The paintings span more than 80 sites along the Zuojiang River in Guangxi, southern China. The cliffs are hot, humid and exposed to heavy rain and typhoons, yet many images remain attached to the limestone. Researchers examined fragments that had already fallen from three sites to investigate how the painted layers were made.
That does not mean the artists simply painted with blood. The study describes a composite material: red clay rich in tiny hematite particles, set into a lime-based layer whose chemistry was altered by blood proteins. The result appears to have formed a hard mineral structure around the pigment, helping it resist the wet and abrasive environment.
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A landscape of thousands of images
Huashan is not a single painted wall. The Zuojiang Huashan Rock Art Cultural Landscape contains more than 80 sites along the river valley, with paintings spread across roughly 260 kilometres. The figures show people, animals, boats, weapons, musical instruments, and scenes that researchers associate with ritual life. Many were painted high above the river, making access part of the challenge.
The paintings are usually associated with the Luoyue people, a community known through historical sources from the region. The new research adds a different kind of evidence: the chemistry of the paint itself. It suggests that the artists’ achievement involved not only reaching the cliffs but preparing a binder that could hold pigment to limestone in a demanding climate.
What the scientists found
The team did not sample intact cliff paintings. Instead, they examined fallen fragments from three sites. They used microscopy and spectroscopy to study the layers, then applied proteomic testing to look for ancient organic material.
The red colour came from local clay containing nano-sized hematite particles. Those particles were enclosed in a mortar containing lime and calcium phosphate. The researchers also detected proteins consistent with blood. In their reconstruction, blood proteins helped trigger the formation of calcium carbonate around the pigment, creating a strong bond with the limestone.
The researchers report evidence indicating that the binder contained a mixture of animal and human blood. They also propose that some human blood may have come from women who had given birth, perhaps connecting the material to fertility beliefs. The chemical analysis supports the material claim; the proposed ritual meaning remains interpretive.
What the evidence can—and cannot—show
The findings describe fragments from three locations, not every painting across the 260-kilometre rock-art belt. The chemistry therefore cannot show that all Huashan images used an identical recipe. Nor does this paper date the paintings: the roughly 2,000-year timeline comes from earlier archaeological dating work discussed by the authors.
The tests do not identify individual donors or, on their own, establish the meaning artists gave the material.
Why the binder matters
The finding helps explain why the paintings survived in such a difficult setting. A conventional loose pigment would have been vulnerable to rain and repeated heating and cooling. A lime-and-blood binder could have created a much more stable surface, locking the red particles against the cliff.
It also changes the picture of the artists’ work. The achievement was not only the ability to climb the cliffs or organise a large workforce. It involved a practical understanding of materials: how a pigment behaved, how a binder hardened, and how a painted surface could survive the climate.
Ancient artists did not leave laboratory notes, so their knowledge often survives indirectly—in the chemistry of a wall, the structure of a kiln, or the wear on a tool. At Huashan, a microscopic layer of mortar may preserve a decision made by people whose names are lost but whose technical choices remain visible.
For more on ancient painted landscapes, see our coverage of prehistoric rock art in India and rock art depicting celestial bodies in Siberia.
