Buried fires crack a porcelain mystery

Pottery takes a leap

Tests conducted by a team from the Jiangsu province-based Nanjing University on samples from the Zhulinkeng kiln complex measured firing temperatures of approximately 1,220 C for the proto-porcelain and 1,190 C for the stamped hard pottery found alongside it.

The figures matter because ordinary earthenware is typically fired at only 700-800 C. Crossing the threshold to 1,100 and above represents a qualitative leap.

"From pottery to proto-porcelain was a true technological revolution in the history of porcelain," says Yang Zelin, deputy director of the Fujian Provincial Institute of Archaeology and lead archaeologist of the excavation.

Even more striking was what the analysis revealed about material selection. According to the archaeological team, potters at Zhulinkeng deliberately adjusted their clay recipes to suit different types of vessels.

For larger containers, such as jars, they increased the alumina content to prevent warping. For smaller pieces, including stemmed bowls, they used a more plastic clay.

Experts say this reflects a sophisticated understanding of material properties. Different kilns within the complex also produced distinct wares, with variations in glaze and firing techniques.

Some kilns specialized in high-quality products, while others focused on more ordinary products, notes Li Zequn, an archaeologist at Nanjing University.

Such standardization points to a remarkably high degree of specialization, Li adds.

One of the most distinctive features of Zhulinkeng's wares is their thick walls and thin glaze.

Yang explains that this was a deliberate choice, unrelated to firing temperature. Instead, it reflected the glazing process and the glaze's chemical composition.

Zhulinkeng's potters chose a fluid glaze that spreads thinly and evenly, producing a distinctive blue-green surface marked by fine crackles, he says.