The mountain's quality clay, the dragon-shaped kilns built into its slopes, and the convenient water transport made this area one of China's largest export kiln complexes in the mid — to late-Tang Dynasty, with wares reaching 29 countries and regions.

"Transforming a lump of clay into a finished piece involves at least 70 steps over 10 days or more," explains Liu Zhiguang, a provincial-level intangible cultural heritage inheritor whose workshop is on the old street.

The first step is clay refining. Tongguan's iron-rich clay is mixed with five other types of earth and sand according to a secret formula, then repeatedly pounded and kneaded to remove air bubbles until it reaches a state of being "malleable but not sticky, soft yet cohesive", Liu says, adding that it is a process governed entirely by the artisan's touch.

Then, with wet hands, artisans coax the spinning clay upward, thinning and shaping it, using just the right pressure. Once dried, the bisque enters the design stage, where Changsha kiln's famed underglaze technique shines.

Minerals like copper and iron are used to create pigments in brown, green and blue.

"Copper turns green under an oxidizing flame, and red in a reduced flame. The slightest variation in temperature or atmosphere changes the color completely," Liu says.