Ancient ceramic iridescence explained by nanoparticles

Researchers from the Universitat Politècnica de Barcelona and the European Synchrotron studied ninth-century Islamic ceramics to understand how artisans created a shimmering, metallic effect.

Centuries ago, potters in the Near East produced ceramics with striking colors and a unique appearance thanks to the use of nanoparticles. Scientists sought to determine the chemical processes behind this effect, which proved difficult to replicate with modern techniques. The artists began by applying a paint containing silver and copper compounds to a glazed ceramic.

During firing, these metals diffused into the glaze and underwent chemical reactions, forming silver and copper nanoparticles within the surface. These particles weren’t simply on top of the ceramic. They became part of the glaze, creating a nanostructured layer that affected how light interacted with the surface. Using X-ray spectroscopy and diffraction at the ESRF and ALBA Synchrotron, the team discovered that the process involved an ion exchange during firing.

Copper and silver ions moved from the paint into the glaze, replacing other ions. The temperature of the firing, between the glass transition temperature and glaze softening, was crucial for this exchange. Differences in the amounts of copper and silver in the paint determined the final color and characteristics of the nanoparticles.

The researchers plan to create and analyze new samples to better understand how different manufacturing parameters influence the outcome, and they also want to investigate the impact of other metals like iron and tin.