Synchrotron radiation-based multi-analytical approach for studying underglaze color: The microstructure of Chinese Qinghua blue decors (Ming dynasty)

• A new methodological approach to describe and determine the underglaze porcelain decors is proposed.
• SR-μXRF and FF-XANES allow identifying the speciation of colorant ions and mapping their distribution.
• Co in tetragonal coordination is the main cause of blue color of Qinghua porcelains.
• The density and the repartition of CoAl2O4 particles define the density of blue color.
• Mn ions have an influence on the color darkness.

In this paper, we develop a methodological approach combining macro-X-ray fluorescence and synchrotron radiation-based techniques (μXRF, full-field XANES and μXRD) to determine the composition and microstructure of underglaze decors of Qinghua porcelains (Ming dynasty). Various transition metal elements (Fe, Mn, Co) are present in the blue decoration of these ceramics and the approach proposed allows for establishing the feature of each. Thus it shows that Fe ions are distributed homogeneously over the whole glaze without any significant difference in blue and white parts. They do not play a significant role in the color. In contrast, Co ions exhibit a heterogeneous distribution with CoAl2O4 particles close to the body/glaze interphase. These particles play a key role in the blue color and, the hue variations seem in greater part to link to their density and repartition. Co dispersed in the glassy matrix is also bivalent and mainly in tetragonal coordination, leading also to a blue color. Mn ion distribution is similar to the one of Co but without presenting local high concentrations associated to Mn based particles. Mn affects the darkness of the color and for the sample without CoAl2O4 particle; it is the main color contribution. The presence of CoAl2O4 crystals was confirmed by μXRD, which revealed, in addition, a variation of cell parameters certainly linking to a Co partial substitution.

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