Metal nanoparticles in contemporary potters’ master pieces: Lustre and red “pigeon blood” potteries as models to understand the ancient pottery

Reduction of metal precursors within the molten glaze is a rather complex route to obtain coloured glaze. “Sang de bœuf”, “pigeon blood” or “flammé” first discovered glazes by the Chinese potters of the Song Dynasty (10th c.) are produced by atmosphere controlled firing of copper-containing glaze on porcelain and stoneware body. Lustre pottery, an Abbasid potters’ innovation (9th c.), offers to the eyes of the connoisseur an iridescent reflection, which is only visible at specular position. For centuries connoisseurs’ interest in these objects has been continuous and the development of transmission electronic microscopy (TEM) associated with energy-dispersive X-ray spectroscopy (TEM-EDX) allows us an in depth study of the micro and nano-structure of these objects. A porcelain with red “pigeon blood” decor made by the late famous French-American potter Fance Franck, and lustre stonewares made by the French potter Eva Haudum, have been investigated by TEM-EDX and nanochemical analysis in order to better understand the key parameters controlling the microstructure and the colour of glazes. Although some authors assigned the red colour of pigeon-blood to Cu2O, our results clearly demonstrate that the colour only arises from Cu° nanoparticles. Phase separation of the glassy phase was observed close to the surface. Concerning the lustrewares, analysis confirmed that the alternating reducing and oxidising conditions during the firing lead well to the formation of metal-free/metal-rich alternate layers in the lustre decor.