An article published in the journal Ceramics International reveals a new methodology that combines two characterization techniques based on synchrotron light to study Chinese blue and white porcelain from the Ming dynasty, a lineage that governed in China from 1368 to 1644. This innovative protocol could contribute to elucidate production technology in a wide range of modern and archaeological ceramics.
The first author of the study is the lecturer Josep Roqué-Rosell, from the Faculty of Earth Sciences and the Institute of Nanoscience and Nanotechnology of the University of Barcelona ( IN2UB ), and counts on the participation of members of the University of Toulouse (France), the Museum of Natural Sciences of Barcelona and ALBA Synchrotron.
Studying ceramics to reconstruct the past
It is common to find pieces of ceramics in many archaeological sites that date from the Neolithic period, when the first human settlements appeared. This fact turns the ceramic materials into one of the main focuses in archaeological studies -style, production, etc.- for the historical reconstruction of a place, region or period.
Studies on ceramic technology reconstruct the production technology of ceramics through scientific techniques that determine the selection and preparation of raw materials, formation of the piece, treatment and the decoration of the surface and the firing atmosphere.
Ming dynasty: art and empire
The Ming dynasty, founded in the 14th century by the emperor Zhu Yuanzhang, created great social and economic transformations in China and promoted emblematic building projects such as the Grand Canal, the Great Wall and the foundation of the Forbidden City in Beijing. Although the production of blue and white ceramics goes back to the 7th century AC, the Ming dynasty promoted the progress of the related techniques to ceramic production and exported at large scale towards the South-West Asian area, Eastern Africa, Middle East and Europe.
As part of the study, the research team studied porcelains from the Ming dynasty, decorated under the glaze of cobalt-based blue pigments. These distinctive blue decorations were made with a one-step firing at a high temperature. In particular, the studied samples correspond to a fragment of a big bowl that presents many visible dark spots, from the Chenghua (1464-1487 AC) and the Hongzhi reign (1468-1505 AC) within the Jiangxi area.
Synchrotron light: look but don’t touch
The study determines the firing of porcelain pigments and the reduction-oxidation conditions during its making. Therefore, the team carried out X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF) experiments at the CLÆSS beamline in the ALBA Synchrotron.
These non-destructive mapping techniques enabled the spatial determination of chemical variations in porcelain decorations associated with the development of dark spots. In particular, the research team characterized the distribution of iron and manganese ions in the porcelain matrix.
The cobalt-based blue pigments can have varied origins. For instance, during the 1279-1423 AC period, people used a cobalt mineral rich in iron from Persia that formed the typical dark spots on the blue decorations. Later, the spread use of Chinese cobalt mineral rich in manganese provided the formation of manganese-rich dark spots.
According to the conclusions, during the firing of porcelain, iron and manganese ions diffused and moved from major to minor concentration regions. During its cooling, the ions crystalized in the shape of the oxide minerals rhodonite and hausmannite-jacobsite, intermediate compounds, and this facilitated the identification of reached temperatures during its production. The detailed study of iron ions with the XAS technique became an efficient tool to assess the reduction-oxidation record in the porcelain glaze.
Roqué-Rosell, J.; Pinto, A.; Marini, C.; Prieto Burgos, J.; Groenen, J.; Campeny, M.; Sciau, P. " Synchrotron XAS study of Mn and Fe in Chinese blue-and-white Ming porcelains from the second half of the 15th century ". Ceramics International, January, 2021. Doi: 10.1016/j.ceramint.2020.09.123