Corrosion Mechanisms in Early-Song-Dynasty Bluish-White Porcelain from the Nanhai One Shipwreck: Cream and Ash-Green Glazes

In this study, two early Song Dynasty bluish-white porcelain samples produced at the Hutian kiln in Jingdezhen and recovered from the Nanhai One shipwreck were analyzed to compare corrosion mechanisms under identical marine conditions. The chemical compositions, microstructures, and corrosion morphologies of the samples revealed two distinct corrosion mechanisms. The transparent cream-colored glaze was primarily affected by dissolution–reprecipitation, with α-FeOOH as the primary corrosion product. By contrast, the matte ash-green glaze contained abundant spherical amorphous SiO _x with submicron granular structures, the corrosion and crystallization of which resulted in densely distributed white spots and arc-shaped surface cracks, with FeS ₂ as the main corrosion product. These findings suggest that microstructural differences in the glazes, attributable to immature ceramic fabrication techniques during a technological transition period, are key to the differing corrosion mechanisms of these two bluish-white porcelain pieces.