A Sultan's Lakeside Laboratory
On the southwestern shore of Turkey's Lake Beyşehir lie the ruins of Kubad Abad Palace, the summer residence of the Seljuk Sultan Alaeddin Keyqubad I. Built between 1220 and 1236, the complex included a "Great Palace" measuring 50 by 35 meters, a smaller palace, a boathouse, and at least 16 total structures. Unlike other Seljuk palaces located within fortified cities, Kubad Abad was a remote retreat. Excavations, which began in the 1960s, uncovered the most significant feature of the palace: thousands of polychrome wall tiles.
These tiles, arranged in patterns of eight-pointed stars and interlocking crosses, display a variety of figures. There are depictions of the Sultan himself, courtiers, animals like foxes and peacocks, and mythological creatures such as sphinxes, griffins, and the double-headed eagle—the symbol of the Seljuk Sultanate. The diversity of this imagery on palace walls is unique in the Islamic world of the period. While some tiles use a simple underglaze technique, the most scientifically advanced are the lusterware tiles, which required a complex, multi-stage production process that was a type of medieval nanotechnology.
Firing Nanoparticles into Glaze
The iridescent sheen of lusterware comes from a thin layer of metallic nanoparticles suspended in the glaze. Creating this effect was a delicate and unpredictable process that Seljuk artisans perfected. First, the stonepaste tile body was fired. Next, it was coated with an opaque, tin-based white glaze and fired a second time. The final step was the luster firing.
Artisans would paint a mixture of copper and silver oxides, combined with ochre and vinegar, onto the glazed surface. The tile was then placed in a kiln for a third firing at a lower temperature, around 600°C to 700°C. At this temperature, the artisans deliberately starved the kiln of oxygen. This created a reducing atmosphere, where carbon monoxide stripped the oxygen atoms from the metal oxides (CuO and Ag₂O). This chemical reaction, known as reduction, left behind a thin film of pure copper (Cu) and silver (Ag) metal nanoparticles embedded in the softened glaze surface. The size and distribution of these nanoscale particles determine how they interact with light, producing the metallic effect. This precise manipulation of redox reactions predates the formal scientific understanding of oxidation and reduction by centuries.