The word 'indigo' originates from the Roman term indicum, which means a product of India. Indigo can be obtained from a variety of plants but in Japan, the dye is primarily extracted from the plant Persicaria tinctoria.

In Japanese, indigo dying is known as ai-zome (藍染め) and the oldest evidence of Japanese indigo dyeing dates back to the 10th century. It is believed that indigo was originally imported to Japan from China. Japanese ai-zome dyeing has its roots in the Heian Period (794 - 1185) but ai-zome culture really exploded during the Edo Period (1600 - 1868) when various laws were enacted forbidding lower classes from wearing silk, and cotton became a popular choice. Because ai-zome is colourfast on cotton as well as being hard-wearing and slow to fade, the dye became the colour of choice for Japans lower classes. 

The indigo plant Persicaria tinctoria  grows throughout Japan and is well suited to Japans climate. Shikoku Island and the Awa region (present-day Tokushima) are especially suited to indigo farming due to the regions rich soil and abundant water supply. The Awa region was one of Japan wealthiest areas due largely to indigo production and continues to be Japans dominant area for indigo production. Read more about Japanese kimono fabrics here.

In addition to its beautiful and hardwearing colour ai-zome indigo also holds a number of special qualities which made it an indispensable tool for both the everyday Japanese farm worker as well as the warrior Samurai classes. Ai-zome indigo is widely acknowledged to have antibacterial, flame repellent and dirt repelling qualities. This made it the perfect choice of dye for farmwear or ‘boro’ clothing, fireman's coats as well as for the undergarments worn by Samurai. Because wearing indigo-dyed clothing helped to prevent infections, protected from the elements and created a flame retardant barrier, ai-zome or ‘Japan blue’ became synonymous with the clothing of the Japanese working and Samurai classes. Today antique kimono clothing dyed with natural indigo is a highly prized collector's item with firemen's coats and boro kimono selling for thousands of dollars and upwards.

Indigo dye is carefully extracted from the leaves of the indigo plant Persicaria tinctoria through a detailed and labour intensive process. There are actually five basic materials needed for Japanese indigo dyeing: sukumo (the leaves of the Japanese indigo plant), fusuma (wheat bran), sake, hardwood ash and lime.The process of extracting the indigo pigment from the raw plant material requires time and patience. The component of the plant responsible for the deep blue colour called indican is released through a process of fermentation which involves composting the leaves in order to encourage the development of bacterial cultures. Piles of leaves are composted for three and a half months. The bacteria generated through the composting process helps to release the dye pigments from the leaves. Once the indigo plant leaves are picked the indican starts to revert to indoxle through a natural enzymatic reaction. Combined with alkali and oxygen (generated through the process of composting) the indoxle is transformed into indigotin, which is what we call the ‘indigo’ pigment. Traditional indigo dyeing relies solely on natural materials and uses no synthetic chemicals of any kind.

Once the indigo leaves have been adequately prepared and fermented they are placed into large vats (around 540 litres) and mixed with water. The temperature of the vat needs to be kept stable at around 20 - 25 degrees C. In order to maintain a steady temperature the vats are often buried into the ground. The fermentation process defines the quality of the final colour and ideally, sponge-like foam (called ai-no-hana or indigo flowers) will form at the top of the vat. Once the fermentation process is complete textiles are submerged within the vat for up to 30 mins at a time. The textiles are then removed, squeezed dry and allowed to hang on a rope. This allows the dye to oxidise and thus fix its colour. Just after a textile is removed from the ai-zome vat it looks dark green. Once it has oxidised it takes on its final blue colour. The soaking and oxidising process is repeated up to 30 - 40 times until the maximum depth of blue has been achieved.

• Shira Ai (white indigo) 
• AsagiUsu Ai (light indigo) 
• HanadaRuri Kon (lapis lazuli blue) 
• Tetsu Kon (iron blue) 
• KachiNasu Kon (eggplant purple) 
• Kame Nozoki (looking at the vase)
  

Today the majority of indigo dyeing takes place in the historical area of Tokushima, located within the prefecture of Shikoku. Working with indigo dye is often a family affair with some of the remaining indigo workshops being 9th or 10th generation indigo dyers. One of the last remaining Edo-era dye houses to engage in indigo dye production is the Higeta Indigo House in Mashiko, Japan’s Tochiji prefecture. The house works with 72 vats of indigo dye and can produce over 30 different shade of indigo blue.

Workshops using ai-zome indigo in the traditional way still exist in Japan but the number of skilled artisans is diminishing due to decreased demand for indigo textiles and as well as a preference for cheaper and less labour intensive synthetic dyes. One artisan still working with ai-zome in the traditional way is Toru Shimomura. Having studied natural plant dyeing at Yamagata university,  Shimomura now runs an indigo workshop together with his father in Ohara, about 30 minutes outside of Kyoto named Ai no Yakata. Shimomura states that “Natural dyed indigo has a depth of colour and reflects the light in a way which is very different from textiles made with chemical indigo dyes”. He further states that “Sadly, most ai-zome products sold in Japan are chemically dyed which can’t be helped considering the decreased number of trained traditional craftsmen as well as the reduced availability of good quality natural raw materials”. You can find Shimomura’s workshop and experience the beauty of traditional ai-zome dyeing at the following address:

ADDRESS: Aza Maezunishi, Tokumei, Aizumi-cho, Itano-gun, Tokushima

DIRECTIONS: Ride the Tokushima Bus bound for Kamojima via Nijo from JR Tokushima Station.Get off the bus at Higashinakatomi, then 5 minutes by foot.

Another workshop creating ai-zome clothing and textiles in the traditional way (using naturally fermented indigo) is the Aizen Kobo workshop in Nishijin. Here they produce a range of textiles hand-dyed with natural indigo and often decorated with traditional decorative styles such as shibori (tie-dyeing), sashiko (hand embroidery) and ikat (resist dyeing and weaving). The present head of the business, Kenichi Utsuki, is a third-generation indigo dyer and together with his wife he teaches and practices traditional ai-zome dyeing techniques.You can find the Aizen Kobo workshop at the following address:

ADDRESS: Nakasuji Omiya Nishi Iru, Kamigyo, Kyoto 602-8449, Kyoto Prefecture

A third workshop still practising the ancient art of ai-zome dyeing is the Higeta Indigo House in Japan’s Tochiji prefecture. The craftspeople working at Higeta House are involved in all processes of traditional ai-zome production from yarn making and ai-zome dying right through to weaving. The workshop is one of the last remaining dye houses of the Edo era and they operate over 72 vats of ai-zome dye. 

You can find the Higeta Indigo House at the following address:

ADDRESS: Higeta Indigo Dyeing StudioJonaizaka 1, Mashiko-machi, Haga-gun, Tochigi Prefecture

DIRECTIONS: 15-minute walk from Mashiko Station on the Mooka Railway.Parking lot: Space for two cars

R by 45 RPM: This brand creates men and women’s denim clothing as well as accessories using cotton dyed with natural ai-zome indigo. Their ai-zome denim thread is dyed 24 times by hand. They even have their own cotton loom which they have slowed down so that the woven cotton has an uneven pattern and handmade look. Their clothing doesn't come cheap - expect to pay between $800 - $1200 for a pair of jeans.

Oni Denim: As the name suggest this brand is all about denim. Working with 100% natural ai-zome indigo and custom looms which produce a special soft and nubby style of cotton, expect a pair of Oni jeans to set you back around $300.

Momotaro Jeans: Another Japanese denim brand that works with natural ai-zome indigo. They offer a number of different styles and cotton types. Choose from stiff 'vintage' deep indigo blue denim fabrics to softer more modern styles. Expect a pair of jeans to set you back around $280.

You can find cotton (momen) dyed with natural ai-zome indigo for sale by the meter at Shibori Dragon- The fabrics are dyed in the Azumino district of Japan, hence the name Azumino-momen. Expect a meter length to set you back around $13 excluding shipping. These fabrics are perfect for sashiko projects! 

 At Fabric inspirations, you can find beautiful printed cotton dyed with natural indigo. As the company is based in the UK shipping is cheaper than from Japan if you are EU /UK based. The fabric is available by the bundle, meter or half a meter. Expect a meter to set you back around $14 excluding shipping.