The Discovery of the Indigo Plant and Dye
From ancient cultures to the modern society, the cultivation of the indigo plant has changed civilization
What is indigo?
Indigo is a tropical plant that belongs to the genus Indigofera. It has pinnate leaves and clusters of red, white, purple, or yellow flowers. Indigo is also a blue vat dye obtained from the indigo plant. The dye was first introduced into international trade from India during the Greco-Roman era. The Greeks named it Ινδικόν meaning Indian or from India because they were infatuated with this deep shade of blue, as were other Europeans. The word was adopted in Latin as indicum.
Indigo in ancient civilizations
The first ancient cultures to use indigo dye from both animal and plant sources is traced back to the Egyptians, Greeks, and Romans before 2000 BC. They used it on painting, cosmetics, medicine, and manuscripts. These cultures derived Tyrian purple dye from the secretions of Murex snails that were common in eastern Mediterranean coasts. The snails would be crushed, left in alkaline salt water for three days, and then boiled for up to ten days. They also derived indigo from the woad plant (Isatis tinctorial). The indigo dye extracted from woad had a lower concentration than the true indigo. Eventually, woad was replaced by the true indigo, which was more concentrated, and easier and cheaper to produce.
In ancient Mesopotamia, a cuneiform tablet was discovered from 600 BC with a recipe for dyeing wool blue by repeatedly immersing and airing the wool. Another discovery was an indigo-dyed linen fragment that was found wrapped around mummies in the pyramids of ancient Egypt. Archaeologists dated this textile fragment from the Fifth Dynasty, roughly 2400 BC.
The most recent discovery of the oldest indigo-dyed fabric happened in Peru, when archaeologists Tom Dillehay and Duccio Bonavia were excavating the prehistoric site of Huaca Prieta between 2007 and 2008. The site used to be a dwelling covered by a mound and turned into a temple, where small scraps of woven cotton with indigo-dyed patterns were found and dated around 4,000 to 6,200 years ago.
The indigo dye was also known for centuries to many Asian cultures, such as Indian and Japanese. The Indians were the first producers and traders of indigo dye to Europeans, who had been using an identical dye from the woad plant. This changed when the Portuguese explorer Vasco da Gama discovered a sea route to India that was established for direct trade of indigo with India, the Spice Islands, China, and Japan. This route was shorter and less dangerous than the land routes that had been previously used. The Indians produced various shades of blue cotton and silk fabrics in vibrant colors and rich textures. They were also known for adding block print designs and exquisite embroidery. These fine fabrics were reserved for royals and figures with political authority.
India introduced indigo to Japan through the Silk Road route during the Edo Period (1600–1868), and it was known to the Japanese as aizome. Because indigo was rare and expensive, it was reserved only for aristocrats and royals. Later on, the Japanese discovered that indigo-dyed fabric repelled insects, was flame retardant, and had antibacterial qualities. For these reasons, indigo-dyed garments became indispensable to everyday Japanese workers, Samurai soldiers, and firefighters. These lower classes dyed their cotton and hemp fabrics with aizome because they were banned from wearing silk.
Indigo in North America
In the 1560s Latin America, Spanish explorers discovered an indigo plant species (Indigofera suffruticosa) and cultivated it in their Guatemalan colonies, as well as export it to Europe. The English and French began the cultivation of indigo in the West Indies colonies. Indigo production continued to increase in the 17th century in the New World. The French colonists of Saint Domingo produced the best quality dye and became the major producer of indigo. The English colonists, on the other hand, began producing indigo in 1655 when they captured Jamaica. By 1740, sugar had replaced indigo in Jamaica as the main crop.
In North America, the English settlers experimented with indigo and other plants in the 1670s. They discovered that the Indian and Guatemalan species produced the most dye. In Louisiana, the French colonists had cultivated successfully the indigo plant. In South Carolina, indigo was introduced by Eliza Lucas, a young woman who experimented with the extraction of indigo dye on her family’s Wappoo Plantation. After several trials, she grew successfully the first indigo crop in 1744 and she shared seeds with her neighbors. From that time on, indigo became the colony’s second-most-important cash crop after rice. The economy of South Carolina boomed with the cultivation of indigo in the 18th century.
Synthetic indigo dye
During the 18th century, the Republic of Genoa became famous for supplying indigo dye and trading indigo-dyed cotton and linen in Europe, particularly France and England. One of the cloths they traded was a deep blue, sturdy, cotton cloth which was ideal for workers in the shipbuilding docks, the mines, the factories, and other tough jobs. This cloth was named Bleu de Gênes (the blue of Genoa), and later jeans in English. Italian manufacturers exported large quantities of Bleu de Gênes to the French town of Nîmes. Over time, the French developed their own durable blue cloth named Tenue de Nîmes (clothes from Nîmes), which the English and Americans later named denim. This cloth was weaved in a pattern of diagonal twill lines and had two different sides: one side that showed blue warp yarn and the other side that showed white weft yarn.
In the 19th century, the necessity for durable clothes in the American working classes along with the great American Gold Rush skyrocketed the demand for natural indigo dye. As this demand grew in the clothing industry, so did the pressure to find a cheaper alternative to produce it. In 1865, German chemist Adolf von Baeyer experimented on the synthetic production of indigo from isatin. The results, however, were impractical until 1897, when chemistry giant BASF developed the first commercial synthetic indigo dye from coal tar. Indigo-dyed clothes were no longer reserved for royalty, but they had finally transitioned into the working classes.
Nowadays, the synthetic indigo dye has replaced the natural one because of its superior color saturation as well as its easier and cheaper production. There are still a few producers of natural indigo that offer products and dye, mainly to crafters for handmade items.
The indigo plant
The indigo plant belongs to the genus Indigofera in the pea family (Fabaceae) with over 750 species of flowering plants. The plants are native to tropical and subtropical regions of the world from Asia through South Africa. Most of these plants are shrubs with pinnate leaves and clusters of red, white, purple, or yellow flowers.
Several species are used to produce the indigo dye, especially Indigofera tinctoria and Indigofera suffruticosa. Other species are used medicinally because of their analgesic and anti-inflammatory properties. Some indigo plants, however, like Indigofera endecaphylla are toxic. If consumed by humans, they can cause diarrhea, vomiting and even death.
The process of making indigo dye
Indigo is a vat dye. Yarn or fabric is dipped into the dyeing vat. When it is pulled out, it comes in contact with oxygen and the color molecules bind onto the surface of the yarn fibers.
The production of indigo dye is an arduous and expensive process. The dyeing process starts when the harvested leaves of the Indigofera plant are soaked in water and left overnight. The leaves release an amino acid called indican which contains glucose. Lime is added to the water. Then, workers beat the mixture for several minutes to oxygenate it. The mixture turns blue and creates a thick paste. This paste is then collected, pressed into molds, dried, and cut into “cakes.” The cakes are hardened further and then grounded into indigo powder ready to be used.
 An organic compound produced by the oxidation of indigo dye with nitric acid and chromic acids.
 An inorganic mineral composed of calcium, oxides, and hydroxide.