Shell method: The leaves are piled in one meter high layer in a warehouse where they are moistened and brewed regularly every three days. New leaves are added and sprayed with water during the entire operation. The temperature rises progressively according to the fermentation and can reach 70 ° C. The pile is then covered with a straw mat to retain heat and fermentation continues for one hundred days. The leaves are then crushed, drained and formed into shells or aidama which are dried. So that they can be used for dyeing, these balls are crushed and the fermentation is reactivated by addition of warm water. The dye is directly extracted from the leave ball (which requires filtering).
Indigo starch method: After harvesting, the leaves are left to dry for two days. Then, they are put to ferment in a tank covered with a small layer of water. The fermentation can take up to 20 hours depending on the ambient temperature.
The liquid is then collected and filtered. It is beaten to make him absorb oxygen and oxidize. Precipitation is done by adding an alkali (caustic lime or ash lye).
The deposit is washed, boiled and filtered. The paste, called indigo starch, is then formed into cakes.
Dyeing of papers is performed in two ways: pulp dyeing (sukizome) or sheet dyeing (hitashizome by dipping or hikizome by brushing).
To dye paper by soaking, the sheets are plucked one by one between two wooden sticks by their small side. This will keep the sheet flat during soaking.
Usually three jars of dye are prepared with decreasing concentrations. The paper is dipped in the less concentrated dye jar and oxidation occurs in the air; the paper is then soaked in the little bit more concentrated dye. After oxidation, the sheet is dipped into the third jar with the strongest concentration. The process can be repeated several times to obtain a color more or less intense. The sheet is dried by exposing the surface to air; the color changes by oxidation.
