The team used a compound of calcium hydroxide and graphene quantum dots in a water solution and applied the material in ancient wall paintings in three tombs of the Tang Dynasty (618-907). "Research shows that the new material is small (an average of 80 nanometers per particle), uniform in size, and very sticky, thus making it good at reinforcing the wall paintings," Wei Bingqing, a CNEM dean, stated.
Carbonate, which commonly exists in ancient murals, is the most easily damaged material, Wei said. He noted that once the calcium hydroxide is applied to the wall painting's surface, a chemical reaction with carbon dioxide to create carbonate protects the painting. Calcium hydroxide can even perform better after nano-crystallization with its surface activity and stability largely being enhanced, Wei said.
In contrast, organic materials that are widely applied in wall painting protection are less compatible with the painting and can cause them to chalk and turn yellow in the long run, Wei added.
Using nanometer calcium hydroxide to protect wall paintings was proposed by Italian scientists in 2000, and scientists from around the world tried for nearly 20 years to find a proper solution to synthesize nanometer calcium hydroxide, Zhu Jinmeng, a research fellow of the CNEM team, said. "But breakthroughs could not be achieved in the size and permeability until today".
Wei said the team would try to develop better materials and further promote their use for wall painting protection in China.