Guardians of the Great Wall

Meticulous, repetitive loops, simulating real situations, reproduce the weathering that can be brought about over hundreds of years or more, and make it possible to develop corresponding reinforcement measures. Such processes are closely monitored by sensors and cameras, among other equipment.

Wang says, the idea of building such a laboratory to deal with the surface weathering mechanism of earthen sites and sandstone cave temples, and to develop solutions for it, came from his predecessors, including renowned heritage conservation scholar Li Zuixiong (1941-2019), Wang Xudong, who's now director of the Palace Museum in Beijing, and Guo Qinglin, deputy director of the academy.

They found that effective tests on small samples are often carried out to no avail in the real practice of restoration. It's natural for them to consider the size of the samples.

These scholars began studying the weathering of the earthen relics in the 1990s. Since the laboratory was officially put into use at the end of 2020, the academy has been simulating diverse climate conditions and testing on samples of earth taken from areas nearby key archaeological sites around the country. The samples show similar features with the earth used in the construction of these ancient sites.

In recent decades, the academy's conservation team has been promoting their research at more than 200 locations in 16 provincial-level administrative regions, and is aiming to build a database of the information collected and analyzed. Their work involves research and investigation, design of reinforcement measures, execution and effectiveness evaluation, Wang Yanwu says.

So far, the laboratory has preliminarily completed the exploratory research on the weathering mechanism of the sandstone North Grotto Temple in Qingyang, Gansu province, and the corresponding prevention and control technology. Research on the Mogao Caves will also be carried out in the laboratory.

Wang Yanwu says it has also developed a series of materials and equipment especially for protection of these structures, as well as reinforcement techniques, such as anchoring, grouting and propping, as well as formulating technical standards for their implementation. Together with anti-weathering technology, such as those using chemical or biological methods, or covering the relics with a sacrificial layer or protective shed, they have formed a technical system of earthen site preservation.

International cooperation is emphasized. Wang Yanwu notes that the lab has introduced and further developed the soft capping technique from the School of Geography and the Environment, Oxford University, which is usually applied on limestone and masonry artifacts, and experimented to protect the surface of earthen relics by covering them with a layer of moss or grass, in the hope of reducing drastic changes caused by temperature, humidity or rain.

The lab is also working with academic institutions including Oxford and the Northwest University in China on dealing with weathering. The Getty Conservation Institute in the United States will be involved in the future as well, Wang Yanwu says.