The Mind, Body, Dye Connection

Traditional indigo dyeing in Japan's Yoshino River Valley

To prepare for my upcoming trip to Japan, I am reposting last August’s almanac entry about Japan’s traditional indigo cultivation and dyeing process. Enjoy!

THE HARVEST

The Yoshino River Valley on Japan’s smallest island is prone to heavy monsoon rains starting in late August. They cause the valley to flood and be unsuitable for most crops. Persicaria tinctoria (the legume Japanese indigo is extracted from) is a perfect match for two main reasons. One, it matures in late July. By the first monsoon rains in August, farmers have finished their harvest. Two, when the harvest concludes and the valley floods, the river brings carbon-rich soil. This allows farmers to grow the legume on the same land each year and makes this corner of Japan famous for indigo. Once harvested, persicaria tinctoria goes through a year-long drying, fermenting, and extracting process before it can be used to dye. 

Figure 1: A sixth-generation indigo farmer on his field that is ready to be harvested in Tokushima, Japan.

ANCIENT CHEMISTRY

What chemically makes a compound a dye is its ability to create color and stick to fabric. With trial and error, civilizations have discovered which plants contain these two properties and how to process them.

Most natural dyeing is a relatively simple process where dyers make a concentrated tea with the plants and steep the fabric. Indigo is not soluble, so it goes through a more convoluted fermentation to be used as a dye. Each society that worked with indigo found its unique way to ferment native plants containing indigo into dyes. 

In Japan, the process called aizome, has been practiced for hundreds of years and requires a series of complicated and tedious steps that few craftspeople still practice (figure 2). 

Figure 2: 1) Mature persicaria tinctoria 2) Sukumo 3) Indigo fermentation vats 4) Finished fabric drying.

THE AIZOME PROCESS

1. Composting: The harvested persicaria tinctoria leaves are separated from the stems, finely chopped, dried for two months, and then piled in small buildings with earthen floors. Bacteria and microorganisms break down and oxidize the leaves. This process is incredibly hot and stinky- the fermentation rooms can reach 150 degrees Celsius and ammonia, with its notable scent, is the reaction's main output (figure 3). 

   Each week marks the labor-intensive task of turning, rebuilding, and watering the four to six-ton piles. After four months, the piles have transformed into a dried, dark blue soil-like substance called sukumo. 

Figure 3: A simplification of the nitrogen cycle that occurs during the indigo process. Persicaria tinctoria is a legume that converts atmospheric nitrogen (N2) into nitrogen plants can use (NH3). Nitrogen is one of the building blocks of the indigo plant. During the composing phase, the plant breaks down, releases some of that nitrogen into the atmosphere, and the cycle continues. 

2. Reducing: Sukumo itself is not a dye as it is not water-soluble. But, it does contain indigo and the microorganism needed for the second fermentation- a process that reduces sukumo, making it a dye. 

   The most important ingredient in reducing sukumo is a mix of local wood ashes. The higher quality of the wood ash, the better the indigo will ferment. Aizome craftspeople carefully select which trees the ash comes from and concentrate it by repeatedly adding it to boiling water, letting it separate out, and redrying it. 

   The wood ash, wheat bran, and sake are then kneaded into wetted sukumo and left overnight to rest. The alkalinity of lye reduces sukumo with help from microorganisms that feed on the wheat bran and sake. 

   The paste is then steeped in water and stirred every morning and evening to ferment for three days. Once the fermentation reduces, the dye vat is filled to the top and lime is added to maintain the PH. It rests for around ten days, during which it must be constantly watched and adjusted to foster fermentation. 

3. Dyeing: Fabric has to be carefully lowered into the vat so as not to introduce oxygen to the balanced mixture. Fabric emerges from the vat a yellow color then quickly turns to blue in the presence of oxygen (the reduced indigo gets oxidized). 

   Indigo is unlike any other dye in that it layers onto fabric. For other natural dyes, the fabric must steep in the dye vat longer for a deeper color. Indigo, on the other hand, must be dipped and then exposed to oxygen over and over for a deeper color. 

Aizome has been practiced in Japan since the Edo Period- a peaceful time 400 years ago when Japan saw a rise in traditional arts and crafts. Since then, the steps and ingredients of aizome have been relatively the same. They have been passed down from one master to the next during 10- to 15-year-long apprenticeships. Apprentices do not learn written, step-by-step recipes but how to use intuition and inherited knowledge to make the craft their own. 

THE MIND-BODY-DYE CONNECTION

Aizome first became popular with Samurais who wore it under their armor. The superstitious warriors believed wearing the dye led to winning because it prevented bacteria, protected wounds, and kept them cool and comfortable. Clothing dyed in the auspicious dye holds many healing and balancing properties, it is anti-bacterial, anti-inflammatory, and regulates temperature (figure 4). 

Figure 4: Japanese firefighters also wore aizome garments as they are naturally fire retardant up to 1500 degrees Fahrenheit.

Today, Aizome has virtually no market. In the late 1800s, a German chemist discovered how to derive synthetic indigo from petroleum and a suite of toxic chemicals, which at best are skin irritants (an ailment natural indigo-dyed clothing helps alleviate) and at worst are carcinogens, neurotoxins, and persistent pollutants. Manmade production was so cheap that natural indigo fell by the wayside. Although many governments have banned the use of the toxic chemicals used to make synthetic indigo, the recipe stays the same as manufacturers move to countries with laxer environmental and workers’ health regulations.

The most noticeable difference between natural and synthetic indigo is that natural indigo decomposes and fades as it ages. Synthetic indigo remains on not just clothing, but also in bodies, minds, rivers, soils, and oceans.

NOTES

https://www.pref.tokushima.lg.jp/en/japanese/natural_culture/traditional_culture/awa-ai

https://www.frontiersin.org/articles/10.3389/fmicb.2018.02196/full

https://traditionalkyoto.com/shopping/indigo-aizome/

https://www.uk.emb-japan.go.jp/itpr_en/2305aizome.html

https://www.visvim.tv/dissertation/processing/aizome.html

https://www.nytimes.com/2018/11/26/t-magazine/traditional-indigo-dyeing-japan.html

https://kingpinsshow.com/is-natural-plant-based-indigo-dye-more-sustainable-than-synthetic-indigo/