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Table 2 Typical deteriorations in Guangyuan Thousand-Buddha grotto

From: A quantitative evaluation based on an analytic hierarchy process for the deterioration degree of the Guangyuan Thousand-Buddha grotto from the Tang Dynasty in Sichuan, China

Category Deterioration Description Figure
Stability deterioration Scaling off Surface of the stone is peeled off as a slice or crust due to salt dissolution and crystallization, temperature fluctuation, freezing or weathering View full size image
Detachment Surface of the stone is out of the grotto body and forms a cavity but is not peeled off View full size image
Water deterioration Water leakage, water incrustation inside the grotto due to rainfall, surface runoff and capillary water View full size image
Body loss The grotto or sculpture show a certain volume loss from its initial state View full size image
Cracks Includes three types: one is weathering fracture, often occurring on the surface; second is stress fracture, often extending to the inner stone, and may cause body loss or complete breakage; last is structural fracture, often closing, smoothing and appearing as a group View full size image
Plant damage Plants grow in the cracks of grotto; the root may lead to more cracks View full size image
Weathering deterioration Rock powdering weathering Surface of the stone is softened and peeled off because of temperature and humidity fluctuation, freeze–thaw cycles, water and salt activity View full size image
Deep loss The plaster layer of paint in the grotto is peeled off from the stone View full size image
Salt crystallization Soluble salt dissolved and crystallized because of temperature and humidity changes View full size image
Pigment layer peeled off Paint layer of grotto flaked and broke away from the grotto or sculpture View full size image
Paint layer craquelure Paint layer of grotto cracked but not peeled off from the grotto or sculpture View full size image
Scratch or graffiti Scratch or graffiti by human activity View full size image
Improper repairing The grotto was repaired by improper materials or methods in the past View full size image
Surface pollution Sootiness on the grotto or sculpture by smoke from the past. Dust and weathering products cover the surface of the grotto View full size image
Microorganism pollution Microorganism grows on the grotto View full size image