I attended the “Indigo Colloquium” at the UC Berkeley Botanical Garden.
Why indigo, I wondered as I signed up? What is it about that particular color that attracts such interest?
Turns out indigo is the color of denim. And since over a billion pairs of blue jeans are sold every year, how they are colored is important commercially and environmentally.
Coming at the subject from a level of complete ignorance, I learned that weekend that many plants throughout the world produce the color blue. Remember woad? If you were taught history in the dark ages as I was, you may remember that the Celtic warriors who opposed the troops of Julius Caesar when he invaded Britain terrified the soldiers because their faces were painted a fierce blue from the woad plant.
Woad (isatis tinctoria) is now considered an invasive weed in California. But it can be grown in home gardens to produce the blue dye.
Indigo, however, produces a stronger blue. Hundreds of different plants producing the color indigo are grown throughout the world, and the most popular for dyeing is persicaria tinctoria, otherwise known as polygonum tinctorium. The common term is Japanese indigo.
Indigo is a dye that adheres to the textile without the use of mordants. That’s a fixative produced by alum,iron, copper,or tannic acid often mixed with an acid like vinegar. For that reason, working with leaf-based indigo is safer for the home dyer.
I love the idea that over hundreds if not thousands of years, people have experimented with creating gorgeous color from plants that grown nearby. The process is a series of chemical reactions to release the color from the plant. For the home dyer, this involves heating the harvested leaves in a pot of distilled or rainwater to release the indican in the leaves, and adding a base such as baking soda, washing soda or ammonia to increase the pH to 8 or 9, which helps the hydrolysis of the indican to produce the molecule indoxyl. Then air is introduced to the mix, allowing the indoxyl to combine with oxygen to produce indigo. Finally, in order to make the color water soluble the mixture is reduced over heat with the addition of thiourea dioxide (helpfully available from the drug or craft store as Rit Color Remover). Add your previously wetted fabric to the dye for up to fifteen minutes, lift out carefully and hang to dry. The exposure to air makes the dye color fast and produces the final blue.
The color changes in the dye-in-process are fascinating. The flowers of the plant are actually pink. The composted or heated leaf brew is reddish-brown. Adding the alkali produces a yellow color, and agitating it to add air turns it to green. As the reduction process happens, and you add your fabric, your textile appears yellow green. Taking it out of the dye bath and hanging it up exposed to air turns it first turquoise, then indigo blue.
Indigo can also be produced synthetically. However, this is a petroleum based product (from benzene) and so toxic that synthetic indigo dye is no longer produced in this country. Most of the jeans sold in the world today are colored with synthetic dye made in China.
Some researchers have created a microbiology-based indigo by gene transfer from persicaria tinctoria into ecoli. It may be commercially viable in the future, but so far indigo manufactured through microbiology has not proven cost-effective.
But for now, there’s an opportunity for the revival of dyeing with natural sources of indigo to become a real alternative to synthetic dyes. If enough farmers can be persuaded to grow the indigo plants so that minimal dye batch sizes of consistent color are produced, then clothes manufacturers will be interested.
That’s the hope anyway.
In the meantime, I now know how to work the process of cloth dyeing into my story, in which there’s tension between old ways of doing things as rediscovered by a group of ageing hippies in Northern California, and the encroaching modern world. Can the old be made new again? As I learned, that is very possibly fact, not fiction.