The seeds are sown at the time of the spring equinox (mid March). They are transplanted in May and the first harvest takes place in summer. Plants are sorted, left to dry for two days and the leaves are separated from the stem by threshing
Direct method: The leaves are crushed and left to ferment in a warm water tank allowing bacterial activity. Lime or ashes are added to maintain a fixed alkali rate. The fabric is placed directly in the bath. Oxidation occurs when the cloth is removed and exposed to air. This method gives pale blues. It is necessary to repeat soaking and exposure to air and provide fresh leaves for a more intense color.
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.
Double fermentation method: The leaves are prepared according to the conventional fermentation method. Then the dye is kept in jars for several months without stirring to prevent rapid oxidation. When oxidation starts, it forms purple bubbles on the surface called "indigo flowers. This foam is removed, dried and crushed to reduce it in pigment powder. These pigments are used to form sticks by mixing them with animal glue.
Dyeing of paper is made in two ways: paper pulp dyeing (sukizome) or paper sheet dyeing by dipping (hitachizome). 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 beat 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.
