Indigo is a solid, insoluble, dark blue crystalline powder. It does not bind with the fabric at all nor does it chemically bond with the fabric, it forms a mechanical bond.

To make indigo soluble in water, it is necessary to reduce it with a suitable reducing agent like bacteria, Zn, Sodium hydrosulfite, etc. Once the indigo is reduced, it becomes colorless and water-soluble. After the removal of oxygen (by the reduction method), it then has a high affinity for cellulosic fiber. The reduced indigo dye easily enters the open spaces of the fiber, and then the dyed fibers are exposed to air, due to which the dye molecules oxidize back to their insoluble forms. The dye molecule gets trapped inside the fiber and colors the fabric permanently.

Indigo is used for various purposes, for dyeing wood, cotton, leather, and silk. The indigo application is safe for dyeing silk.

Dyeing Silk by Indigo Hair dye:

Silk can be easily dyed using pure indigo hair dye with the help of the following steps:

The silk cloth is stretched with the help of an embroidery hoop, and then resist like wax or starch paste is applied to protect the design.
The dye paste is prepared by mixing the indigo hair dye with water.
The silk cloth is then reversed, and the indigo dye is applied on the backside of the cloth.
As the paste oxidizes, it changes color from dark green to dark purple-black. Different shades can be obtained by interrupting the oxidation by air, heat, and light. Applying paste in sunlight gives the best results.

Dyeing Silk by Indigo pigment stick:


There is another way for Dyeing silk material called as dyeing with the Japanese Indigo pigment stick.


The oxidized bubbles that are formed on an indigo dye vat are dried and binded together to form Indigo sticks. The indigo dye vat is traditionally too alkaline in nature; it preserves and insulates the cloths.


The indigo dye is used in combination with a soybeans mordant. To apply dye on the silk, put some drops of water or mordant on the porcelain tile and gently rub the exposed area of the indigo stick on the porcelain tile in the circular motion, till the desired shade is obtained.


The Dye is applied on the silk in layers and for deeper shades the stick is applied evenly on the surface or it is applied till the desired shade is achieved. At last the cloth is kept aside for drying.


The sticks are very soft and gentle, so they should be handled with care.


Sources:

  1. Article header.doc
  2. http://www.indigopage.com/how/silk.htm
  3. http://dyeingworld1.blogspot.com/2010/01/indigo-dyeing.html