Were these ancient rock images painted with human blood?

The Zuojiang Huashan Rock Art Cultural Landscape was created over the course of nearly 700 years, between the fifth century B.C.E. and the second century C.E., by the Luoyue people—a matriarchal, hunter-fisher-gatherer society that lived in southern China. The images are found across 80 sites along a 260-kilometer stretch of river cliffs. Given that the area is battered by regular monsoons, the art is remarkably intact, especially compared with murals made hundreds of years later in other parts of the country.

“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,” says Meng Wu, a chemist at Shandong University. “The material stability of this art has long been an unsolved mystery.”

https://www.science.org/content/article/were-these-ancient-rock-images-painted-human-blood