This superb Han dynasty jar has a robust shape imitating that of the bronze (hu) and is covered with a thin brownish-green glaze. The introduction of glazing—which provided an impervious coating to a clay body—marked a technological breakthrough in Chinese ceramic history. High-fired glazed pots were made as early as the Shang and Zhou dynasties (about 1600–256 BC). Potters gained practical technical knowledge of the reaction between the metallic oxide in the glaze and the kiln atmosphere to modify the color of a glaze.