Islamic Luster Ware: Clay, Glazing, and Kiln Techniques

Introduction: The Islamic Luster Ware Tradition

The area of Central Asia is one that, even as we look at it today, reveals a richness of design, color, and texture in fabric, architecture, and earthenware that can be traced to the earliest periods of Islamic society and culture. That large geographical area — consisting of Anatolia, Syria, and the Arabian Peninsula, eastward through Iraq and Iran, Uzbekistan, and Afghanistan to the Indus Valley in Pakistan and the western boundary of China — is where ancient medieval Islamic luster ware artifacts have been found in abundance. Many of the ingredients that went into producing the clay, paints, and glazes used in the luster ware, as well as the firing techniques, were closely guarded secrets of the artisans who produced them. Today, however, modern technology and academic research through archaeology, history, and language have helped us unlock the secrets of the ancient Islamic artisans.

The modern tools of technology, such as X-ray diffractometers (XRD), optical and electron microscopes (SEM and TEM), and electron microprobes help us identify the materials used by ancient artisans. The natural resources of the different areas in Central Asia were essential to the clay, paints, and glazes used in the production of luster ware. Using these modern tools and research, we can not only identify the different areas where the works originated, but we can also identify the ingredients of the formulas of the clay, paint, and glazes, and even the temperatures at which the pieces were fired.

The Clay

The clay used to throw the different pieces would have varied with the soil and clay consistency from region to region. The basic ingredients of clay are alumina, silica, and water. The levels of iron and other impurities found in the clay would vary from region to region. The actual clay particles in what is commonly referred to as "clay" are quite small, flat, and electrically charged, touching on just two sides. The particles of clay react when water is mixed with them, causing an attraction and plasticity that allows the clay to be moldable and worked into the different forms created by the artist.

The various earth elements — such as the salinity of the water mixed with the clay, the levels of granite in the soil, and even the agricultural uses of the land and the animals grazing on the land — would each impact the clay that came from that land. It is the soil clay composition that, although affected by the firing processes, has a significant impact on the end product.

The artists would have acquired their knowledge of the importance and significance of clay composition through their learning under the instruction of skilled and experienced artisans, and eventually through their own working experience and experimentation with different soil clay compounds. They would have used soil clay combinations from different terrains to create clay recipes, and the most successful of these recipes would have been carefully guarded secrets. They would have learned that the amount of gases in the soil clay compound would determine the amount of bubbling during the firing process, and that it would contribute to the texture and hardness of the finished piece.

"A major difference between clay compositions used for earthenware and stoneware relates to the relative concentration of elements (fluxes) that lower or raise the melting (eutectic) point. Mismatch between firing temperature and flux-rich clays can result in vessel failure with development of excessive glass phases and gas formation ('bloating') causing partial or complete vessel collapse ('slumping')."

Once having assembled their clay ingredients, the artists would have added water to the recipe to create the texture and thickness of clay they wanted to work with for each specific piece. Some of these clay composition recipes would have been hybrids, reflecting the various soil locations that were being used. Without the clay recipe, and without the benefit of modern technology to analyze the soil clay composition, it would have been almost impossible for other artists to recreate a hybrid piece — which may have contributed to such pieces being in high demand.

The artists would have kept a detailed description of the source of their clay formula, and would have continually looked for new and better formulas by experimenting with different natural resources. Having created a recipe, the artist would have tested it: rolling a piece of clay into a single coil — if there were cracks in it, it was a poor recipe; if it showed no cracks, it was a good recipe.

The artisan would also have relied greatly on his own sense of touch. Mixing the clay with his hands, he would have sensed its thickness, texture, stickiness, and weight. No mechanics of a wheel or other piece of technology can replace the artist's own senses in creating the perfect clay formula.

The Islamic potters were drawn to Chinese porcelain, which was a closely guarded secret of Chinese potters. To recreate it, Islamic potters experimented with the levels of quartz in their clay recipes. While they did not succeed in recreating Chinese porcelain, they did create something entirely new: "However, in their efforts to imitate porcelain, they discovered that the addition of tin oxide in amounts of up to fifteen percent makes a glaze opaque and produces a smooth, creamy white skin. It is a perfect background for decoration." What they created was luster ware — an original Islamic pottery that would become as sought after as the Chinese porcelain that had served as its inspiration.

Conclusion: Legacy of Islamic Luster Ware

These tin-glazing techniques yielded a vast wealth of luster ware, which was as desirable to the Chinese and to the Western world as was the Chinese porcelain that inspired the art of tin-glazed pottery. The Islamic luster ware tradition stands as a testament to the ingenuity of Central Asian artisans who, in seeking to replicate a foreign ceramic ideal, ultimately created an enduring art form entirely their own.