New perspective on Jun glaze corrosion: study on the corrosion of light greenish blue and reddish purple glazes from Juntai Kiln, Yuzhou, Henan, China

Abstract The ancient Chinese Jun Porcelain has of typical high fired calcium silicate glaze. After observation of Jun porcelain shards excavated from Juntai Kiln in Yuzhou, Henan Province, China, two pieces with light greenish blue glaze and reddish purple glaze are selected for study as special corrosion samples buried in soil environment. Taking the corrosion of each phase of the overall glaze into consideration, the chemistry compositional and morphological structural features of the earthworm-walking patterns and their surrounding white area (corroded zone) in the glazes are compared and studied with optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDS), Raman spectroscopy (Raman) and electron microprobe (EPMA): during the firing of Jun Porcelain, the dendritic and columnar crystals coming out of the glaze and mostly in surrounding corroded areas are identified as wollastonite (CaSiO 3 ), which provides active sites for localized corrosion. The wollastonite crystalline phases have preferential corrosion initiated by pitting corrosion relative to glassy phase, leaving dendritic or columnar pits and craters to dissolve into calcium ions and silicic acid and losing into the burial environment. Some calcium ions in the surface pits react with dissolved inorganic carbon (DIC) from the soil to form calcium carbonate (CaCO 3) precipitated on the surface of the glazes. The cracks formed during the cooling process and the interconnected craters caused by crystals dissolution can provide channels to facilitate the progression of the corrosion. This research is of great significance to the study of the corrosion mechanism of ancient porcelain and the conservation of its cultural relics. It has changed the traditional view that porcelain is corrosion-resistant. At the same time, the study of the corrosion process and characteristics of ancient porcelain can provide reference for modern ceramic research and corrosion protection.