The plant is cut at ground level when it is in bloom and the leaves are turning to a reddish color because indigo content is at its highest. It will bloom again three months later and it is possible to make a second and third cut.
Direct method : The plant is used immediately: the plants are fermented in a vat of hot water for bacterial activity. Lime or ashes are added to keep a fixed alkaline rate. The dyeing is done directly in the bath.
Shell method : The fresh plant is crushed, drained and shaped into balls (shells or aidama) which are dried. These shells to be used then, are crushed and fermentation is reactivated by adding warm water. It is then up to the first process.
Indigo starch method : The plants are fermented in a tank covered with a thin layer of water. Fermentation can last up to 20 hours depending on ambient temperature. The liquid is then collected and filtered. It is whipped to make him absorb oxygen and oxidized which will permit its flocculation. The precipitation is done by adding an alkali (caustic lime or ash). The deposit is washed, boiled and filtered; it is called indigo starch, the dough is then shaped into loaves.
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.
