Study On The Mechanism Of Surface Dissolution And Protection Of Typical Cliff Stone Carvings In Guilin

As a national key cultural relics protection unit,Guilin stone carvings,mainly cliff carvings（including cliff carvings and cliff statues）,more than two thousand pieces exist,possessing precious historical and cultural value.Under the effect of long-term natural erosion such as sun and rain,stone carvings are subject to different degrees of damage,thus the study of the mechanism of stone carving dissolution in the natural environment is of great significance.Focusing on the surface dissolution damage commonly found on two typical stone carving groups in Guilin（the Longyin Cave cliff carvings and Xishan cliff statues）under environmental influences,dissolution experiments that simulated the environmental characteristics of two typical stone carvings groups were conducted.The comparison of the dissolution characteristics and patterns of the two types of limestones were conducted and studied under different p H values（p H=3.5 and p H=6.5）and different environmental actions（dry-wet cycles,hydrostatic immersion,rainfall cycles,and temperature difference cycles）,and the annual dissolution rate of stone carving was calculated based on the results including the mass loss rate of stone samples.The protective effects of two acrylic resins（Paraloid B-72 and B-67）on limestone under acid rain immersion and washing was studied.Early warnings on the risk of dissolution of the Longyin Cliff Carvings and the Xishan Cliff Statues in Guilin were conducted to provide the basis for the conservation of the carvings.The major conclusions are as follows:1.Acidic solution was the main cause of mass loss of stone samples under different p H values and dry-wet conditions,which gradually increased with the number of dry-wet cycles.After 50 dry-wet cycles of p H=3.5,the mass loss rate of stone samples reached 0.068～0.078%.2.Rainfall cycles had a greater impact on dissolution than temperature difference cycles under different p H and circulation,and the acid greatly promoted dissolution.After 50 cycles of p H=3.5 rainfall cycles,the mass loss rate of stone samples reached 0.326～0.364%.3.The annual dissolution rates of the two stone carvings were calculated based on the final mass loss of the stone samples.Under different test conditions,the dissolution rate of stone carvings reached 2.30×10^-4～2.70×10^-3cm/year.4.The fastest damage time of the stone carvings and statues was calculated based on the annual dissolution rate.Without effective protection measures,the cliff stone carvings and statues in the research areas would be eroded and flattened within75 to 1303 years under various environmental conditions.5.The protective layer on the surface of Guilin limestone using Paraloid B-72and B-67 acrylic resin materials could effectively reduce the water absorption rate of Guilin limestone and had a certain acid-resistant performance.