The organic Indigo Vat

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.

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. 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 it 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 length bamboo fabric (using pattern threads later to be gathered in a shibori pattern) as the first piece to be dyed in my indigo vat. The Japanese shibori pattern called monumental is made by weaving parallel lines into a piece of cloth, then gathering the stitches tightly.  When the cloth is dyed, the folds resist the dye to form a pattern. On the loom, pattern threads are woven into a ground cloth in regular intervals. When taken off the loom, the pattern threads are gathered, as in traditional shibori, and knotted. The cloth is dyed, and the compressed areas in the folds resist the dye to form the woven pattern. After dyeing, the pattern threads are pulled out, and the ground cloth remains.

The fabric is dyed by dipping it in the indigo vat for ten to fifteen minutes, then rinsed in clear water and hung up to oxidize. The more times it is put into the vat, the deeper the color. After two dips in the vat, with about a half hour to oxidize between each dip, the cloth 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 completely dry overnight, the pattern threads were removed by cutting the knots at the edges very carefully. As the pattern threads are pulled out the shibori pattern is revealed.

The final step is to let the indigo cure on the cloth for about a week, afterward 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.