Indigo production has been a long-standing part of Japan’s history. The artisan group BUAISOU is dedicated to preserving ancient indigo dyeing techniques. Indigo dye comes from the leaves of the indigo plant, which are harvested, dried, and then fermented in a vat of ash lye, wheat bran, and calcium hydroxide to create the dye. Sukumo—the type of dye that the group uses—has properties that prevent the dye from bleeding onto other fabrics and materials.The intensity of the dye is dependent on how long the fabric is dipped into the vats of dye. The indigo color only appears when the dye is oxidized after the fabric is dipped into the vat and exposed to air.
Source: Spoon and Tamago