Production Process of Qing Dai (Indigo Naturalis)

Qing Dai (Indigo Naturalis) is a blue powder extracted from indigo-containing plants and produced using traditional methods. Below is an overview of its production process.

1. Selection of Raw Materials

The primary raw materials for Qing Dai are indigo-producing plants, including:

• Polygonum tinctorium (Japanese Indigo) 

• Isatis tinctoria (Woad) 

• Strobilanthes cusia 

2. Extraction of Indigo through Fermentation

1. Harvesting the Plants

   • Fully matured indigo plants are harvested and washed to remove impurities.

2. Soaking and Fermentation

   • The plants are placed in large containers filled with water and soaked for 1–2 days.

   • Microbial activity breaks down the indigo precursors (such as indican), leading to the formation of indigo.

3. Addition of Alkaline Solution

   • Limewater or wood ash is added to create an alkaline environment, which helps the indigo to precipitate.

   • During this process, blue indigo particles begin to separate and settle.

3. Purification of Qing Dai

1. Collecting the Precipitate

   • The water is drained, leaving behind a thick blue sludge (indigo paste) at the bottom.

   • This paste is further washed to remove impurities.

2. Drying and Grinding

   • The filtered indigo paste is dried using sunlight or low-heat drying.

   • Once dried, it is ground into a fine blue powder (Qing Dai).

4. Final Processing for Different Applications

• For Medicinal Use: Further refined and used in traditional Chinese medicine (e.g., Qing Dai powder for ulcerative colitis and skin diseases).

• For Dyeing: Used as a natural dye for fabrics and textiles (indigo dyeing).

• For Pigment Use: Applied as a blue pigment in traditional paintings and ceramics.