But for most of Japanese history, blue wasn’t just a colour. It was a living craft, grown in fields, fermented by hand, and passed down through families. And the reasons people wore it tell a story about how closely cloth and daily life were once connected.

Where did Japanese indigo come from?

Indigo dyeing arrived in Japan from China between the Asuka and Nara periods, possibly by way of the Korean peninsula. At first, it was mainly a craft of the aristocracy.

The oldest surviving example is a 200-metre blue silk cord kept at the Shōsō-in treasure house in Nara. In 752, it was used during the consecration ceremony of the Great Buddha at Tōdai-ji temple.

That single cord is now more than 1,270 years old.

How did indigo become everyday clothing in Japan?

Two things changed during the Edo period (1603–1868): cotton and the law.

Cotton was produced in growing quantities, and it took indigo dye exceptionally well. Wearing indigo-dyed clothing soon became common among ordinary people.

At the same time, the Tokugawa shogunate issued sumptuary laws that controlled what each class could wear. Commoners were largely barred from silk and expected to dress plainly. Indigo was one of the few bright colours they were allowed.

So blue spread everywhere:

• Work clothes for farmers and craftsmen
• Noren, the curtains hanging over shop doorways
• Furoshiki, the cloths used to wrap and carry goods

A colour first reserved for the elite became the colour of the street.

Why is Tokushima famous for indigo?

Tokushima, once known as Awa province, became Japan’s most important indigo region. Its dye, Awa-ai, was prized across the country.

The reason was the land itself. The Yoshino River flooded often, which made rice farming difficult. But the same floods left rich soil and plenty of water, ideal for growing indigo.

Making the dye took patience:

1. Indigo leaves were harvested, chopped and dried.
2. They were sprinkled with water and left to ferment for about three months, becoming sukumo, the base of the dye.
3. The sukumo was fermented again with ingredients such as sake or wheat bran before cloth could be dipped.
4. Each dip into the vat added another layer of blue.

Illustration: each dip deepens the blue, one layer at a time.

No shortcut existed. The colour depended on the plant, the season, and the dyer’s hands.

Did firemen and samurai really wear indigo?

Yes. But the stories around why are worth separating carefully.

Firemen

In Edo-period cities built of wood, firefighters wore heavy jackets called hikeshi-banten, made from layers of indigo-dyed cotton quilted together with sashiko stitching. Before facing a blaze, the jackets were soaked in water. Wet, they could weigh more than 30 kilograms.

The main protection came from the thick, water-soaked quilting. Some museum records note that the indigo dye itself may have added a degree of fire resistance.

Samurai

Paintings from the Edo period show warriors wearing indigo-coloured clothing beneath their armour.

What does modern science say about indigo and bacteria?

Modern lab testing suggests the old belief may have had a grain of truth, at least on the fabric itself.

• A study of 16 indigo-dyed fabrics from Thailand found that all of them slowed the growth of Staphylococcus aureus, a common skin bacterium, in lab tests.
• Researchers at the University of Lille found that textiles dyed with Persicaria tinctoria, the same plant used in Japan, showed activity against S. aureus.

At AIZOME, we had our own plant-dyed fabrics tested by independent laboratories. Using recognised textile methods (JIS L 1902:2015 and GB/T 20944.2-2007), the fabric reduced bacterial and fungal growth by up to 99%. That result held after 20 wash cycles. See our lab testing

Where does the name “Japan Blue” come from?

When Japan opened to the West in the second half of the 19th century, visitors noticed the blue everywhere.

The British chemist Robert William Atkinson, who arrived in 1874, is said to have coined the phrase “Japan Blue” after seeing how deeply indigo ran through daily life. The name stuck. Nearly 150 years later, indigo was chosen as the colour of the official Tokyo 2020 Olympic and Paralympic emblems.

What happened to natural indigo?

Indigo cultivation in Tokushima peaked in 1903. After that, cheaper synthetic dyes arrived from overseas, and the fields began to shrink.

It’s a familiar pattern. A slow, natural process gets replaced by a faster, cheaper one, and most people never notice the switch. Today, the blue in most of our clothes comes from a factory, not a field.

Yet the tradition never disappeared. Small producers in Tokushima kept it going, and interest in natural, traditional crafts has brought Awa-ai back into view.

Where AIZOME comes in

Our name comes from this craft. Aizome simply means indigo dyeing.

At AIZOME, we work with plant dyes instead of synthetic ones. And we test our fabrics independently, so the old beliefs can be measured, not just repeated.

Indigo was never only about colour. It was about what touched the skin every day, and choosing it with care.

Maybe that’s worth remembering the next time you reach for something blue.