New evidence for the glazing technique in Changsha kiln coloured porcelains

Changsha kiln ware represents an important status in the history of Chinese ceramics, well-known for its massive production capacity evidenced from extensive archaeological finds both domestically and abroad. It is long known or assumed that Changsha kiln is the pioneer for underglaze painted porcelains, however recent analytical studies suggest otherwise: overglaze, atypical underglaze, or cannot be ascertained microscopically. Changsha kiln glazing technique remains a convoluted issue debatable amongst scholars that is yet to be concluded. To investigate the glazing technique of Changsha kiln coloured porcelains, we track the colour distribution down the glaze using an improved methodological approach: thin cross-section light microscopy and elemental analysis with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and proton induced X-ray emission (PIXE). The samples selected for this study, Changsha bowls with Fe-brown and Cu-green decorations excavated from the Belitung shipwreck, and Changsha Cu-red pieces of a jar and box lid unearthed from the Changsha kiln site of Hunan province, have not been analysed before for the purpose of determining the glazing technique, thereby offering new data to contribute to this scholarly subject. Microscopy results: Thin cross-sections clearly enhance the visibility of colour distribution in the transparent glaze, especially for highly tinting browns and reds. The green glaze, however, is extremely homogeneous and requires elemental analysis to affirm its glazing technique. Elemental results: SEM-EDS line scan and mapping results show that Fe-brown decreases down the glaze (i.e. overglaze), whereas for Cu-green and Cu-red colourations, the levels of Cu are too low to detect an appreciable change down the glaze. With the more sensitive PIXE technique, the distribution of trace levels of Cu in the green and red glaze are mapped out for the first time, providing concrete evidence for Cu-green as overglaze and Cu-red as mid-glaze.