The invention of the lusterware process was a long one, and it probably began in the 8th century in Basra in what is now Iraq. There a handful of potters began experimenting with the new techniques learned in part from the Tang Dynasty craftsmen, and part from earlier glass coloring technologies. They first developed metallic paints, based on compounds of copper and silver in a suspension of water and perhaps vinegar, to produce a wide variety of colors and iridescent shines.
The Basra potters also attempted to emulate Tang Dynasty porcelains, by creating clay recipes that they hoped would produce the hard, bright-white porcelain vessel body. But they couldn't do it--porcelain requires kaolin clay not available in the near east. The closest the Basra potters could come was called Samarra body, a high quality paste but of a creamy color. To mask the cream and provide a white canvas for their metallic paints, the Basra potters began experimenting with opaque glazes.
A ceramic glaze is, essentially, a thin layer of glass attached to the surface of a pot which provides both water-proofing and decorative shine. Making an opaque glass is one of the great secrets of the glass-making industry developed in the Levant about this time. The Basra potters first achieved an opaque glaze by under-firing an alkali-lime glaze, which creates a mass of tiny bubbles covering the vessel. Metallic paints on such a glaze produce a blue-yellow iridescence, but not the bright colors of the Tang pots. Another problem was the glazes cracked during firing because of differential thermal expansion rates of the clay body and the glaze layer. By the ninth century, the Basra potters had begun to add tin oxides to whiten the glaze and lead oxides to solve the cracking problem.
Metallic-based paints fired onto a leaded glaze were a revelation. The metals in the paint and the lead in the glaze work together during firing in an as-yet-not-understood process, creating a variety of colors and luminescences undreamed of by Tang potters.
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.
