Japanese Natural Indigo
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Natural indigo is one of the oldest dye. Indigo has been known to man for more than 4000 years. It is well-known that in ancient Egypt and ancient India, indigo was used for dyeing. Also in Asia we have an evidence of using indigo. A Chinese old book in about third century before Christ says "Blue from indigo plant is deeper than its origin." The direct translation of this proverb is "Blue from indigo plant is deeper than its origin." actually means "one attains a greater mastery than his teacher". I think this proverb corresponds to that of English "The new rose becomes more beautiful than the old rose"
The word "indigo" originally means a dye from India. Now a day indigo also means the colorant in natural indigo. Indigo can be obtained from a variety of plants such as Indigofera, Storobilanthes and Polygonum. In Japan Polygonum is used to make natural indigo.
Oldest evidence of indigo dyeing in Japan is appeared in 10th century. In 18th century, every class of the people wear indigo products.
Polygonum, Japanese indigo plant

Polygonum had been cultivated all over Japan. Yield was highest in Shikoku area. Climate of this region called Tokushima (ancient name, Awa) is good for the plant. The river called the Yoshino supplies much water and good soil. About 200 years ago, this region, Awa, was very wealthy as a production center of natural indigo.
Spring is the planting season and in summer Polygonum grows to be cut. Leaves are separated from stems by wind. Leaves collected are subjected to fermentation.

Grown leaves in summer are cut to make natural indigo dye   Leaves are fermented for 3 months. Water is added every 3-4 days and the leaves are mixed.   Soil like natural indigo is formed by the fermentation

Soil like dye which contains indigo colorant is made after this fermentation. Fermentation must be accomplished under wet and warm conditions. Every three days the farmer must mix and add water. After the mixing, the plant was covered with a straw mat (of a rice plant). The farmers think the production of indigo is to bring up a baby, they call the straw mat bedclothes and they call this room a bed-room. If the leaves are not moist enough, temperature does not raise and the fermentation does not proceeds well. In such a case, they say the dye caught a cold. Again and again they mix. By the fermentation for 3 months, they can get soil like product which contains 3 to 5 % of indigo. The farmers pack and send them to dyers.

Indigo cannot be used for dyeing directly because it is not soluble to water. Dyeing is quite different from painting. Painting is to attach the pigment to the surface of the cloth. But to dye cloth colorants must penetrate into fiber. Unsoluble indigo cannot penetrate into fiber. However reduced form of indigo can be soluble to an alkaline solution. Modern method for the reduction of indigo is to use reducing reagents such as hydrosulfite. In ancient time people found to use fermentation for the reduction of indigo.

A vessel for indigo vat   Bubbles indicate the time to dye   Soaking years in the indigo vat

In the vessel lied under ground, 7kg of Japanese natural indigo, 1kg of bran or flour and ash of wood are placed. The dyers check the alkalinity of the solution by their tongue. Best pH of the solution is around 11.5. After several days indigo is reduced, which is indicated by blue bubbles on the surface of the vat. These bubbles are formed by reoxidation of the reduced indigo. Dyers call these bubbles "flowers of indigo" In such situation the dyer can dye yarns. Since the concentration of reduced indigo is very low, one must soak many times to get dark blue.

After industrial production of synthetic indigo began, the production of natural indigo drastically decreased, because the colorant in natural indigo and synthetic indigo is identical. European people stopped using natural indigo because industrial indigo is much cheaper than natural indigo. As increase in the production of synthetic indigo, also the production of Japanese indigo plant decreased. However, Japanese natural indigo was not defeated completely. In the era of economic growth in Japan, 1960's and 1970's, people did not take notice of traditional dyeing and dyestuff. The tradition was on the verge of disappearance. But at present several farmers grow the plant and the tradition is inherited. And people are becoming interested in such traditional dyeing. The traditional one is much more expensive than the industrial products but Japanese people find the value of the traditional products.

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