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.
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
A vessel for indigo vat
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
traditional one is much more expensive than the industrial products but Japanese people find the
value of the traditional products.