The rock paintings of Huashan in southern China, bordering Vietnam, could have been preserved for at least 2,000 years due to the unusual composition of the ancient paint.
According to a new study published in the Journal of Archaeological Science, a mixture of lime mortar and blood may have been used during its preparation.
The Huashan complex is included in the UNESCO World Heritage List. Thousands of images have been carved into the boulders at more than 80 locations, stretching for about 260 kilometers. They depict people, boats, animals, weapons, musical instruments and other characters. Some paintings are at least 2 thousand years old.
Their preservation is particularly surprising because the region is characterized by an extreme subtropical monsoon climate. here there is intense heat, torrential rains and frequent typhoons.
In order to study the composition of the paint and not to damage the images themselves, the scientists examined the sections of the rock fragments lying at the foot of the three sections of the complex. Using electron microscopy, they studied the layers of paint, and spectroscopic methods allowed to determine their mineral and chemical composition.
It was found that the red pigment was probably made from local red clay, which contains microscopic particles of iron oxide, nanohematite. These particles were found in the outer layer of the artificial solution, which contained lime and blood protein components.
The researchers assume that the blood could simultaneously perform both technological and symbolic functions. When mixed with lime, blood proteins may have contributed to the formation of calcium carbonate around the pigment particles. As a result, a strong organic-inorganic structure was formed, which bound the pigment to the surface of the rock and could significantly increase the durability of the paintings.
"This stable organic-inorganic bond system testifies to the complex technological processes used by the creators," the authors of the study note.
Scientists have also discovered human serum proteins. This allowed us to assume that human blood could have been used for the preparation of the paint. The authors link this practice to the cultural and religious beliefs of the Loyue people, who are credited with creating these paintings. The Loyue people followed matriarchal traditions, and the blood of women who had recently given birth could symbolize life, fertility, and renewal.
At the same time, the researchers stress that the origin of the blood still remains a hypothesis and requires further study.
Until now, the creation of the Huashan petroglyphs was considered primarily as an extremely labor-intensive process; painters had to work on steep and dangerous cliffs and carry large quantities of paint there. The new data show that the craftsmen faced not only physical but also complex technological problems, including the development of a durable binding material.
"These results provide a new understanding of the creation of prehistoric rock art and show that it was not so much a labor-intensive as a technologically complex project," the authors of the work concluded.
