Research On Derusting And Painting Of Cultural Relics In Sheet Metal Bronze Based On Hydrogel Method

Gilt-bronze is an exotic flower in Chinese historical relics, for its unique technology and exquisite shape, which has been an important part of metal artifacts. However, many excavated gilt bronzes were covered with a thick layer of patina masking the original luster that was often descaled by various methods. The presence of plated layer on gilt-bronze made it exceptionally challenging to remove the patina above the plated layers without any depletion and change by traditional cleaning methods. A complex gel cleaning method was put forward to descale the patina from gilt-bronze based on the exploration of its corrosion mechanism.The filth of oils and smokes was a common pollution on the surface of cultural relics in China, which was chiefly corresponding to the burning of incense and candle. As a common pollution apperacing on the surface of the Dazu Stone Carvings, it deeply influenced their apperance. Thanks to the data by scanning electron microscopy with X-ray energy dispersive spectrometry (SEM-EDS) and infrared spectrometer (IR), the characteristics of pollution were revealed for the establish of gel cleaning method.Considering the shortcomings of traditional cleaning methods, the gel cleaning method were selected for descale gilt-bronze and remove the filth of oils and smokes on the colored drawing layer of cultural relics.The following works have been accomplished by experiments:(1) Ultra-depth microscope, SEM-EDS, XRD, IR and Raman were applied to analyze the corrosion products of the plate layers, revealing the corrosion mechanism of gilt-bronze and the characteristics of corrosion products, which will provide important reference data for selecting the protective methods;(2) Bronze wares of Han Dynasties excavated in Chongqing are decorated with plating patterns, maintaining a gorgeous luster through modern times after clearing away the covered patina with the gel rust remover. In this paper, a plated fragment from the Wushan County Museum of Han Dynasties was characterized by OM, SEM-EDS, XRF, XRD and XPS. The results showed that the bronze fragment was gilded with a ca. 3 ?m thick gilded layer and ca.20 ?m thick silvered layer. The high concentration of Hg and Hg-rich intermetallic compounds confirmed the existence of mercury-gilded/silvered technology, e.g. Au9Hg in the gilded layer and Ag13Hg7 in the silvered layer. An ordered stripe structure was observed in the gilded surface, corresponding to the formation of rod-like, intermetallic Au-Hg compounds. Specifically, a high concentration of Au was detected in the silvered layer. The exploration of gilded/silvered bronze casts light on this ancient technology and the benefit of identifying, protecting and reproducing it;(3) A hydrogel cleaner, composed of polyvinyl alcohol (PVA) and Carbomer, and added by formic acid and cysteine, is studied as a derusting agent that can not only remove the patina from the surface of plated bronzes successfully, but also keep their original luster. The experimental results show that it has good viscoelasticity and three-dimensional network structure in a relatively wide pH range; the gel system achieved to remove malachite, azurite and cuprite effectively following by the gradual desolution of patina without the reaction with plated layer. After the derusting process, the gilt-bronzes showed a gorgeous and bright luster, and even exhibiting a clear and exquisite decoration;(4) After using IR to analyze the filth of oils and smokes on the surface of colored drawing layer, we select Carbomer as carrier, ammonia as cleaning component, and N, N'-bis (2-hydroxyethyl) oxamide to adjust the viscosity of the gel cleaning agent. By characterizing the property and cleaning effect of the gel cleaning agent, the results showed that:the gel cleaning agent has good viscoelasticity and three-dimensional network structure, as well as water retention and sustained release, so it can achieve the purpose of cleaning by releasing the cleaning component slowly reacted with oils and smokes, and avoid the penetration of solution into the colored drawing layer effectively. After cleaning, the colored drawing layer recovered its original appearance.