Fig. 4

The indigo paste production process. a Strobilanthes cusia leaves after 24 h of fermentation. b Removal of leaves using a net (called jiu in local name). c Oxygenation after adding lime water to reduce the pH. d Detail of wooden tool (dongzhong) used for oxygenation. e A half section of a gourd (Lagenaria siceraria) scoop used to take out indigo paste at the end of the process