Origin of the self-organisation of Cu degrees/Ag degrees nanoparticles in ancient lustre pottery. A TEM study

A metallic lustre, the first man-made photonic crystal, is a thin film formed just below the surface of medieval glazed potteries that gives iridescence. The multilayer spatial distribution of Ag degrees/Cu degrees metal nanoparticles in 12th/14th century (Fatimid and Iran/Kashan style) lustre glazes is illustrated with TEM measurements. This very particular distribution differs from those observed in previously studied Mesopotamian, Moorish, Renaissance and modern samples. The synthesis method is discussed in the light of old recipes and experimental evidence. Particle size and distribution resulted from repeated controlled heat flashes provoked by surface organic residue combustion and/or rapid introduction of the pottery into the hot kiln. Melting of Ag/Cu metal demonstrates that glaze surface temperatures close to 1000-1100 degrees C were achieved at the peak temperature cycle.