During the Daoguang period of Jiaqing in the Qing Dynasty, Yixing once produced a kind of clay called "Azure Clay", which was of good quality. After firing, it showed dark liver color and flashed blue light, and its texture was delicate and moist. It was said to be the best variety of purple clay in previous dynasties. In order to pursue the color effect of "Azure Mud", artists have devoted themselves to research and added a proper amount of metal oxide and cinnabar mud to purple mud to reproduce the color effect of "Azure Mud". Its formula is not disclosed.

Zisha mud, also known as Zisha Mine, is called "rich soil", commonly known as "azure mud", "red brown mud", "bottom groove cleaning mud" and "red mud", and is the main raw material for making purple sand pots (vessels). It is buried hundreds of meters under the Huanglong Mountain rock formation, between the "nail mud" seams. In Yixing, purple clay can only be found in clay mines in Dingshu area. Finished products made of purple clay, such as purple clay pots, purple clay pots, purple clay vases, purple clay tea sets and other purple clay handicrafts. Thanks to drinking tea, the teapot is the most common, which is characterized by not taking away the aroma of tea and having no smell of cooked soup. The wall of the teapot absorbs the smell of tea, and the empty teapot is filled with boiling water for a long time.

The ancient cloud "Azure Blue" in azure mud, with blue light flashing in dark liver color, is named after the burnt color, which is easily confused with dark green mud and is one of the precious and rare mud materials!