For more than three thousand years people from many cultures all over the world have used indigo to color fabrics in vivid shades of blue. Its roots can be traced to India, and indigo became extremely valuable as a result of the African slave trade. In the book Indigo, Catherine McKinley states that in Africa, indigo “was used literally as a currency. They were trading one length of cloth in exchange for one body.”
Indigo was introduced to the American Colonies before the Revolution by Eliza Lucas Pinckney. At that time, Indigo was a very difficult crop to grow, and the extraction process was complex and extremely labor intensive. Pinckney grew her first successful crop in 1744 and gave seeds to her neighbors, which began an indigo revolution in South Carolina.
By 1897, indigo was synthesized by German chemists, which brought about an era of mass produced synthetic indigo. It is more challenging to dye with indigo, because it is not soluble in water and must undergo a chemical change in order to bond to a fabric. Toxic chemicals are needed to dye with synthetic indigo.
Today, the organic indigo vat has been reintroduced by master natural dyer, Michael Garcia. His method is based on the traditional vats of Morocco and India in which organic materials such as sugar, plant, or minerals are used in place of toxic chemicals.
I recently took a three day class with Catharine Ellis on woven shibori and the organic indigo vat. It was an amazing experience, and I have since started an organic indigo vat of my own.
Making and maintaining an organic indigo vat is more complex than other natural dyes. The vat must be alkaline, so I have used pickling lime in my vat to keep the pH between 10 & 12. The vat must also be reduced, which is to remove all oxygen from the water. I used dried powder from the henna plant which reacts with the lime to reduce the vat. The fabric is pre-wetted, then dipped in the vat for ten to fifteen minutes and hung up to oxidize the dye. When the fabric first comes out of the vat is is a pale green, and as it oxidizes it turns beautifully blue. It can be dipped as many time as needed to achieve the desired shade.
I wove a bamboo scarf/shawl as the first piece to be dyed in my indigo vat. (See this previous post for more information on the weaving process.) I pulled some of the pattern threads out to make a blue border at the selvedge. I had woven the pattern threads, in brown, all the way to the edges of the fabric.
After two dips in the vat, with time between each dip to oxidize, the fabric was a gorgeous blue. It then had to be neutralized in a vinegar/water bath. The vinegar bath also serves to brighten the color and prevent it from going into a state of reduction again.
After letting the cloth dry overnight, the pattern threads are removed the next morning. The knots at the edges must be cut very carefully…
The final step is to let the indigo cure on the cloth for about a week, then it is boiled in soapy water. Boiling removes the excess dye particles from the cloth and strengthens the indigo molecules, further bonding them to the fiber.