Through a Glaze, Lightly

The art of glazed Ru ware, a delicate pottery made exclusively for the Chinese imperial court, has been lost for nearly 900 years. Now, researchers Pamela Vandiver and Alix Deymier at the University of Arizona in Tucson are hoping to rediscover the process by using light to reveal how the ceramics’ characteristic opalescent blue-green glaze was fired. They are using a Hitachi S-2460N scanning electron microscope to analyze shards of Ru ware to find out what the glaze was composed of, what stages it went through in the kiln and how it interacted with the clay of the vessel to which it was applied.

Researchers are analyzing shards of rare Ru pottery to find out how the distinctive glazes were fired. The method for making the ceramics has been lost for centuries. Images courtesy of the University of Arizona.

Study of similar glazes has indicated that the color and translucence comes from a liquid-liquid phase separation in the microstructure of the layers of glass coating rather than from chemical pigments. The researchers believe that the same holds for the elusive Ru glaze. They are using an SX50 electron beam microprobe from Cameca of Paris to visualize the interaction between the glaze and the clay and to see whether the chemical composition is uniform throughout the layers and consistent in vessels made in different locations.

Samples have been made that attempt to reproduce the ceramics based on their findings, but the glaze is still too transparent and glossy. “The ancient glazes are somewhat opaque, having a satin- or jadelike surface, and they are translucent,” Vandiver said.

A scanning electron microscope image gives clues toglazing stages on a Ru-ware surface: amorphous glass, separated glass (indicated by small pits, where it is etched away) and a crystalline phase (indicated by long dendrites).

Deymier added that they do believe that the research will ultimately lead to a revival of the ancient technique. And then the world will no longer need to rue a lost art.