| More than 7000 pieces of terracotta warriors and horses are buried in the pits of Qin's Terracotta Army, only about 1000 pieces of them have already been unearthed currently, and still nearly 6000 pieces of the rest are expected to be excavated. With the addition of the numerous painted cultural relics which have been discovered in the pits around Emperor Qin's mausoleum, there will be a lot of work to do with the paint protection in the future. Therefore, it's very important to find a kind of material and method of reliable performance and effective reinforcement for the paint protection. After years of unremitting efforts, we have made a major breakthrough on the paint research and protection of the terracotta army of Qin, found the initial good strengthening effect protection method, which has surely laid the foundation of the paint protection for the future work. However, if the protective materials are reliable and reasonable, there haven't particular studies yet. This study is a comparison of the physiochemical properties and aging resistance of the reinforcement materials used in the color protection of the Qin's terracotta army and some commercial materials usually used in the color protection of cultural relics, through which to understand their abilities to withstand the environments and the impacts of different environmental factors on them. Eventually, according to the results, on the one hand, to choose the protection material of a better performance, on the other hand, for the painted terracotta figures which have been protected and reinforced, in their future storage, transportation and exhibition, to make them free from adverse environmental factors and to achieve a long-term proper protection purpose.This research studied the anti-aging property, reversibility and the major influence environmental factors of seven kinds of protection materials by the observation of their film-forming properties and many tests, such as 3-year-long indoor and outdoor natural aging experiments, ultraviolet radiation tests, temperature tests, temperature and humidity tests, high humidity tests, tests with temperature and ultraviolet radiation together, organic solvent dissolution tests and tests in a variety of chemical reagents. And also studied the mechanism why the materials'film turns yellow through the detection and analysis of the membrane materials before and after the aging tests by infrared spectrometer.The research primarily has the following results: 1. The reinforcement material PU(Polyurethane dispersion) used in the paint protection of Qin's terracotta army, turns yellow very easily when exposed to outdoor environment, it would turn to yellow just within 1-2 days in the outdoor in May. This was never expected before. Protective material's discoloration will lead to the changes of cultural relics'appearance. On colored relics, it will change the original color, which is not allowed by the cultural relics'protection principle. This discovery can not only make the painted figures which have already been protected by PU be preserved properly, but also express the protection staff of using PU with caution. And already, this has attracted the attention of the conservation scientists, they are actively looking for the alternative materials of PU at present.2. Results show that:polyacrylate emulsion materials have better stability and reversibility, but there are differences in physical and chemical properties in different brands. This reminds the cultural relics'protection staff must do some tests when selecting the protection materials. The results also indicate that within five kinds of emulsion materials tested, LR9001 polyacrylate emulsion material has the best comprehensive performance. It may be instead of PU to become the reinforcement material for the painted figures of Emperor Qin after some further studies.3. Results show that:comparing the two kinds of protection materials B72 and M30 of organic solvent type, M30's chemical resistance and aging resistance are relatively poor, and B72 has a good comprehensive performance, which can be used as the reinforcement material to the polychrome cultural relics which are dry and free of lacquer layer.4. Through the studies of environmental factors on the influence of PU film's color, it shows that the PU film yellowing is mainly caused by ultraviolet radiation and temperature changing. This provides scientific basis of the proper preservation of the painted terracotta army and other polychrome cultural relics which have already been reinforced by PU.5. Based on the research and analysis of the yellowed PU film by infrared spectrometer, it shows that yellowing of the PU film is caused by the products of the light and thermal degradation.6. According to the literature, assessed the environmental conditions of the terracotta army pits, and put forward some specific protection proposals for the painted figures which have been protected by PU. |
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