Indigo dye, or aizome, is made from the indigo plant. The majority of domestic indigo plant production is based in Tokushima Prefecture. The traditional skills for producing indigo dye have been passed down here for generations by master dyers. Indigo blue (ai-iro), long praised for its deep, rich color, dates back to the 10th century.
The first aizome textiles came to Japan from Southeast Asia. The word "indigo" originally refers to a dye from India. Indigo can be obtained from a variety of plants. In Japan polygonum, or ‘tade’, is used for the natural indigo dye process. The oldest evidence of indigo dyeing in Japan dates back to the 10th century. By the Kamakura period (1192-1333) the Japanese method was well established.
Though the polygonum (tade) plant grows all over Japan, Shikoku Island has long been the main production area in Japan. The Awa region (present-day Tokushima prefecture), with its rich soil and abundant water supply, was especially suited to indigo plant farming. It continues to be Japan's dominant area for indigo leaf production.
Aizome dyeing is a very complicated and long process. The traditional process uses only natural materials and no chemicals of any kind. The fermentation process completely determines the quality of the final dye produced.
Aizome color emerges during the fermentation process. The chemical compound indican contained in the raw leaves is converted into indigo by fermenting the leaves and then eventually making the liquid dye. Cloth is then dipped into this solution and exposed to the air, the color emerging as a result of oxidization. This dipping procedure is repeated many times to further deepen the colour.
In 1880, a chemically synthesized blue component referred to as synthetic indigo was developed in Germany, which saw a rapid surge in imports to Japan while the naturally derived indigo dye experienced a sharp decline in popularity. Recently however, naturally derived indigo dye has gained favor again for its safety factor and lasting color compared to the chemical synthesis.