This year again, we are making precipitated indigo, indigo paste and dried indigo cakes from Japanese indigo grown at the Hitotsuya（ひとつ屋） Dye Plant Farm. We also hope to use this material for something beyond dyeing and develop a product that feels distinctly Hitotsuya.
In Part 1 of this series, we fermented fresh indigo leaves in a barrel, removed the leaves and added slaked lime. This time, we use a small bathwater-transfer pump to circulate the liquid, bring in oxygen from the air and oxidise the blue-forming compounds. Let us continue the process.
The complete method is explained in How to make precipitated indigo, indigo paste and dried indigo cakes. The work can also be seen in our YouTube video on making precipitated indigo.
Making precipitated indigo | From agitation to settling
▼ The fermented indigo liquid already contains slaked lime and has begun developing the blue pigment.
▼ A small bathwater-transfer pump circulates the liquid and draws oxygen into the barrel.
Without the pump, the liquid would need to be stirred vigorously thousands of times. More than 3,000 strokes may be required, and the valuable dye liquid can splash out of the barrel. Hitotsuya therefore uses an inexpensive pump to reduce the heavy agitation work.
This labour-saving method is also described in An Industrial Revolution in Precipitated Indigo Making.
▼ Agitation is complete when the initially blue foam becomes pale, turns white and quickly disappears.
▼ Leave the liquid undisturbed for one to two days so that the blue pigment gradually settles.
▼ Carefully remove the clear upper liquid without allowing the settled indigo to flow away.
▼ The remaining paste is indigo paste; when all moisture is removed and it is fully dried, it becomes a dried indigo cake.
This completes Hitotsuya’s process for making precipitated indigo, indigo paste and dried indigo cakes. The fermentation and slaked-lime stage is shown in How to Make Precipitated Indigo, Part 1.
※ About using a bathwater-transfer pump
This differs from the pump’s intended use. Check the product instructions and keep the plug, switch and other electrical parts dry.