To make a classic lusterware pot, the potter began with a vessel of Samarra body, and then glazed it with an alkaline glaze mixed with various amounts of lead oxide to avoid glaze cracking, and enhanced with particles of tin oxide to obtain a white opaque glaze. The glazed vessels were then fired.
After the pot had been fired and given time to cool, the potters painted the design on top of the glaze with a special lustre paint. Lustre paint was a finely ground mixture of clays and silver-copper metal compounds in a suspension of water, perhaps mixed with vinegar. Early recipes varied, with some using copper alone, some silver alone, and some a combination of silver and copper. The compounds were primarily oxides, but sulfides were an important ingredient, produced by using a sulfur-bearing compound such as cinnabar (mercury sulfide).
After the lustre pattern was painted onto the vessel, it was fired again, this time at about 500-600 degrees C, which is cooler than the first firing. This temperature is below the glaze's melting temperature, and much cooler than the firing temperature at which the ceramic body was made. When the lustre-painted vessel was heated at this temperature, the metal ions (copper and/or silver) within the lustre paint were 'absorbed' into the glaze by exchange with alkali ions (sodium and potassium) from the glaze itself. Following the ion exchange, the metal was reduced and became nucleated into metal nanoparticles. When the final process was complete, the remaining lustre paint was wiped away, and the resulting shine consisting of nano-sized particles of copper and/or silver embedded in the glaze is revealed.
Sources
This project is based on the ongoing research of Trinitat Pradell and colleagues. The main sources utilized for the project are listed on the definition page for lusterware. A timeline for the Islamic civilization is also available for consultation.
An excellent source for further information about Islamic ceramics in general with much data on lustres is the Ashmolean Museum's Web-Based Teaching Course on Islamic Ceramics.
