Technological inventions and innovations in ancient societies can be unmasked through the systematic study of surviving artifacts. Through the application of materials science and engineering principles and probing at the atomic and submicron scale, this research has a twofold goal: 1) to re-evaluate the production technology and raw material selection for the manufacture of the oldest synthetic blue pigment in China’s history, Chinese blue (CB) with major crystal phase BaCuSi4O10, in order to infer materials and technological choices and determination of production events, as well as the relationships of these choices to the social and craft organization of ancient societies, and 2) to harness the unique stable visible-induced near infrared (NIR) luminescence properties of BaCuSi4O10 at the nanoscale through hydrothermal synthesis of BaCuSi4O10 nanoscrolls, and to explore its potential application as novel optical material and fluorescent marker.
Results from the analysis of Chinese blue at the micron to submicron level with scanning transmission electron and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM/TEM-EDS) revealed the presence of micron or submicron-sized BaSO4, (Ba,Pb)SO4 solid solution, Pb3O4, and amorphous SiO2 inclusions whose formation are closely related to raw materials selection and manufacturing processes. Based on possible formation mechanisms and systematic laboratory-based reproduction experiments of Chinese blue and Chinese purple, the rarer mineral witherite (BaCO3) seems to have been used as the source of Ba, though the presence of BaSO4, a more abundant mineral, as an impurity in the witherite deposits could not be ruled out. For the Pb and S accounted in the ancient pigment samples, galena (PbS) and/or anglesite (PbSO4) may have been used as sources. The direct use of galena (PbS) has shown to pose difficulty in the production of Chinese blue and purple, requiring a pre-treatment step. The ancient contemporary bronze and PbO-BaO-SiO2 glass production as well as alchemical and medicinal practices based on Pb-containing compounds, may have provided the technological bases for the transformation of galena into other Pb-compounds such as PbSO4, PbO, or PbCO3 that could lead to the successful production of Chinese blue or Chinese purple pigments.
Pb stable isotope analysis by laser ablation inductively multi-collector coupled plasma mass spectrometry (LA-MC-ICP/MS) suggested that the Pb-source used in the production of the Chinese blue and Chinese purple faience beads analyzed, is the same or similar to other Chinese blue and Chinese purple pigment samples analyzed previously, as well as to contemporary PbO-BaO-SiO2 glasses.
BaCuSi4O10 nanoscrolls with length < 500 nm have been synthesized under hydrothermal conditions. The purity and morphology of the BaCuSi4O10 nanoscrolls was strongly dependent on the synthesis temperature and time, as well as the pH of the precursor mixture. Visible light induced near infrared (Vis-induced NIR) imaging indicated that the BaCuSi4O10 nanoscrolls preserve the characteristic NIR luminescence of the bulk materials. The nanoscrolls are likely to have formed through a rolling mechanisms of BaCuSi4O10 nanosheets during the hydrothermal synthesis, affected by the heat treatment conditions and the pH of the precursor mixture.
