The Seventy-Two Processes of Jingdezhen Traditional Porcelain Making

Part Two: Calcining the Mineral

The process of calcining the mineral began in the Song dynasty. It involved stacking a suitable amount of firewood against the quarrying face and setting it alight to heat the rock. Before lighting the fire, workers would prepare damp straw, thatch, or pine branches, along with an appropriate amount of soybeans and rice wine.

Once the firewood was lit, rice wine could be poured on to intensify the flame if the fire was not strong enough. When the heat reached the right point, soybeans were added, and the fire was covered with damp grass to hold in the heat. As the soybeans warmed, they released oil, helping the fire continue burning and maintaining a steady temperature inside the pile. The rock would then be slowly smoldered for two days.

Under heat, the porcelain stone body expanded. The rock cracked, loosened, or could be further fractured by pouring water onto the heated surface. Workers then used iron chisels to follow the cracks, hammering and prying the stone away from the original rock face. In this way, porcelain stone was extracted and carried out of the mine.

1. Mining Porcelain Stone When mineral stone was extracted by fire-setting inside a tunnel, ventilation and smoke removal were essential after burning. To solve this problem, miners opened several vertical ventilation shafts from the top of the tunnel down into the underground passage. These shafts, known as tianjing, or “sky wells,” created an upward draft and allowed air to circulate.

From the late Qing dynasty through the Republican period, long-established porcelain stone mines in Yaoli, Fuliang County; Chenwan, Poyang County; and Yugan County all had such ventilation shafts in their older main tunnels. These shafts formed convection with the horizontal passages and produced a certain natural draft. Their placement depended entirely on the experience of veteran miners.

Rock blasting, meaning manual drilling followed by explosive blasting, began in modern times. In 1930, porcelain stone mines in Yaoli, Fuliang County, and Yugan County both adopted blasting for mining. The position and depth of the drilled holes, as well as the type and preparation of the explosives, had a major impact on blasting efficiency.

Fireshot ores

Later, the types and formulas of explosives continued to improve. In the 1950s, electric detonators were used to ignite ammonium nitrate–based explosives, including ammonium nitrate–TNT mixtures. This not only increased efficiency but also improved safety.

2. Mining Kaolin Clay

Kaolin is one of the main raw materials used in Jingdezhen porcelain bodies, accounting for about 30 percent of the total body composition. Unlike porcelain stone, kaolin is a loose, earthy material and is relatively easy to mine. Its extraction process was simpler than that of porcelain stone. It was mainly mined through open-pit methods, and when the deposit reached a certain depth, tunnel mining was sometimes used.

The surface of a kaolin deposit was usually covered with a layer of yellow earth of varying thickness. In shallow areas, this layer might be about one meter deep, and in some places the mineral body was even exposed at the surface. In deeper deposits, however, the covering layer could exceed ten meters.

To mine kaolin in the open air, workers first had to remove the yellow earth covering the mineral body. This was commonly called “peeling the mountain skin.” It was one of the most labor-intensive parts of kaolin mining and an important factor affecting production costs.

After the outer layer had been removed, the surface of the deposit still contained yellow earth and other impurities, so the mine bed had to be cleaned further. If the kaolin body was loosely bound, it could be mined directly by flushing it into slurry. If it was tightly compacted, it had to be dug out, broken up by hand, or blasted until it became loose.

Secondary kaolin, washed down the mountainside by rainwater and deposited in low-lying areas, could simply be dug out with hoes. Mines such as Mingsha Gaoling, Dazhou Gaoling, and Xingzi Gaoling were all open-pit hillside mines.

Once open-pit extraction was exhausted, miners followed the mineral body into the hillside by digging tunnels. Wooden supports were set up along the passageways to prevent the loose earth from collapsing. However, because the ground surrounding kaolin mine tunnels was generally soft and unstable, deep tunneling was difficult.

3. Sunken Open-Pit Mining At the Shaziling mine in Fuzhou, the mineral body lay deep underground. Mining there required removing the overburden, opening trenches, and cutting stepped protective slopes. Light rail tracks were laid along the mineral body, while inclined tracks used winches to lift the mined material.

4. Hydraulic Mining At the Dazhou mine, water storage pools were built on the mountain top. By using the natural drop in elevation, workers created water pressure and directed hoses at the kaolin deposits, washing the clay loose so it flowed down the hillside into slurry ponds for washing and processing.

This method was later improved with mounted water guns. The nozzles could rotate in a circular motion, which saved labor and improved working conditions.

The tailings left after the mining and washing of kaolin and clay ores

In the next installment, we will explore the process of transporting stone. After calcining, quarrying, and excavation, porcelain stone and kaolin were separated from deep mountain deposits. Transporting the stone became the crucial step that carried raw materials from the mine to the workshop.

Stay tuned.

Jingbo Library · The Seventy-Two Processes of Jingdezhen Traditional Porcelain Making

Let cultural relics speak, and let history come alive. Follow us as we unlock the thousand-year code of Jingdezhen porcelain.

This article is excerpted from The Seventy-Two Processes of Traditional Porcelain Making in Jingdezhen, China, compiled by the Jingdezhen Municipal Archives and published by Jiangxi Fine Arts Publishing House in 2024.