Natural reinforcing effect of inorganic colloids on excavated ancient jades

Abstract The Neolithic jades excavated from southern China often exhibit a serious corrosion phenomenon called “Whitening”, where the jade mineral aggregates have lost compact textures and transform into loose white powders, which cause a substantial decline in mechanical strength and the jades cannot remain intact. Meanwhile, a glossy hyaline layer with a more compact and uniform structure can be observed on the surface of some whitened jades, exert great influence in the integral structure strength of the jades and can be considered as highly significant natural reinforcing materials. The recent excavation of a workshop for jade processing in Zhejiang Province provided us with a great opportunity to investigate the deteriorated jades and the taphonomic environmental conditions associated with it. In this study, analyses of morphology and compositions revealed that the glassy layer is a composition of geopolymers with silica-alumina gels as the major components, which can also be found between mineral grains of jade crystals closest to the surface. Notably, some jade fragments with a yellowish infusion were found to be mechanically stronger compared to other jades unearthed from the same context, which may be explained by the consolidate effect of iron ions in the soil. These results have demonstrated the remarkable protective properties of soil colloids, and thus proposed that by using soil colloids as templates, consolidants with the natural compatibility with jades synthesized by chemical precipitations of charged inorganic colloidal particles can be a promising solution for jade conservation.