Known as “Japan Blue,” indigo is a rich blue dye celebrated in Japanese fashion. Before the non-native plant found its way to Japan in the third or fourth century — likely brought there by the Chinese and Koreans — the Japanese hadn’t been able to produce starkly blue fabrics, and they quickly fell in love with the natural hanada-iro, or “indigo blue,” dying process.
Indigo had been harvested and used for dying fabric for some time in Greece, Egypt, India, and other countries, and it caused quite a stir when it arrived in Japan. Not only did the Japanese admire the beauty of indigo dye, they appreciated its antimicrobial characteristics and odor resistance. Samurai, for example, wore indigo-dyed fabric under their armor to keep wounds from getting infected, and early firefighter jackets were dyed with indigo, as the indigo dye itself is flame retardant up to 1,500 degrees Fahrenheit. The Japanese also believed indigo could repel insects, and since blue was not a designated noble color, it could be worn by anyone in any social class.
The hanada-iro dying process is almost as interesting as indigo itself. Soaking the green leaves of persicaria tinctoria in water creates a chartreuse bath that is used to soak the fabric. When the fabric is pulled out and left to dry, the greenish dye turns blue as it oxidizes. Darker hues could be achieved with additional soaking time, and the emergence of fermented indigo leaves — sukomo — in the 15th or 16th century allowed the Japanese to produce high-quality, consistent color when dying large amounts of yarn or clothing.
The Japanese first used indigo to dye silk until the second half of the 17th century, when peasants started to grow and harvest the cotton plant. Domestic cotton production boomed, used for military uniforms and kimonos alike, and cotton dyed with indigo created the deepest blues the Japanese had seen. As cotton’s popularity grew, so did Japan’s love of indigo. When Japan opened its borders to foreign dignitaries in the 19th century, visiting chemist Robert William Atkinson noticed an abundance of blue kimonos and allegedly coined the term “Japan Blue.” Today, the color remains so ingrained in the country’s cultural identity that the Japanese national soccer team wears “Japan Blue” on the field.
Samurai, for example, wore indigo-dyed fabric under their armor to keep wounds from getting infected, and early firefighter jackets were dyed with indigo, as the indigo dye itself is flame retardant up to 1,500 degrees Fahrenheit.
Indigo farming, fermenting, and dying require a considerable amount of time and technique, so, as with most things in the modern age, synthetic indigo has largely replaced natural indigo. In 1914, German chemical producer BASF released Indigo Pure BASF, a synthetic dye brought to America by immigrants and used in the manufacturing of American denim. Still, there are a half-dozen farms in Japan keeping the hanada-iro tradition alive, and top-quality fashion brands — 45RPM, Blue Blue, Blue Stone, Porter Classic, FDMTL, and Kapital, for example — continue to use the time-honored craft to dye their clothing.