Abstract
The Dalian () Island shipwreck of the Yuan Dynasty (1271–1368 CE) was located in the sea area of Pingtan (), Fujian () Province, China. A total of 603 Longquan () celadon wares were excavated, some of which have been severely corroded. In this study, two celadon specimens with severe corrosion were selected to investigate the corrosion mechanism in the marine environment. Optical microscopy (OM), scanning electron microscopy equipped with energy dispersive X-ray spectrometry (SEM–EDS), X-ray diffraction analysis (XRD), Micro-Raman spectroscopy, and thermal expansion analysis were applied to analyze the microstructure of the glaze, corrosion morphology, and composition of corrosion products, and the corrosion mechanism was discussed in depth. The results showed that these two celadon wares are opaque matt glaze, in which the anorthite crystallization-phase separation structure with low chemical stability was found, which was more likely to be corroded. There are three possible stages in the corrosion process of the glaze. The first stage is mainly the long-term cation exchange reaction. Then, because of the corrosion of the CaO-rich droplet phase and the crystal-glass phase interface layer, the porous structure and many microcracks may be formed, promoting the corrosion process. Finally, many corrosion craters, caused by the shedding of anorthite crystals, may appear on the glaze surface. The quintinite group minerals in the glaze were probably formed during the corrosion process, which may be related to the marine buried environment and the corrosion of the glaze. This study discussed the influencing factors of the corrosion process of celadon wares in the marine environment from the perspective of microstructure for the first time, which is of great significance to the study of the corrosion mechanism of ancient ceramics.
Highlights
Chinese porcelain was exported overseas as an important commodity as early as the Tang Dynasty (618–907 Common Era (CE)) and was loved by people all over the world in history [1]
In the corrosion process of celadon glaze, the ion exchange seems to be insignificant, and there is no dealkalinised layer formed on the glaze surface, which may be related to the higher pH and salinity of seawater
The two Longquan celadon wares from the Dalian Island shipwreck of the Yuan Dynasty have been buried under the seabed for more than 600 years and corroded severely
Summary
Chinese porcelain was exported overseas as an important commodity as early as the Tang Dynasty (618–907 CE) and was loved by people all over the world in history [1]. More than 90% of the cultural relics excavated by underwater archaeology in China were ceramic wares [4], but there is still a lack of in-depth scientific cognition of the damage to the ceramics in the marine environment, and a systematic protection scheme has not yet been formed. This had become an important issue that urgently needs to be resolved in the protection of cultural relics excavated underwater. The corrosion mechanism of the celadon glaze in the natural environment has not yet reached a consensus, and there is a lack of a comprehensive understanding of the various factors affecting the corrosion process, which is obviously not conducive to the subsequent treatment and protection work
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