Indigo what is it

  • Written by Virginia Jelatis

In addition to economic motives, indigo production also succeeded because it fit within the existing agricultural economy. The crop could be grown on land not suited for rice and tended by slaves, so planters and farmers already committed to plantation agriculture did not have to reconfigure their land and labor.

Indigo, a plant that produces a blue dye, was an important part of South Carolina’s eighteenth-century economy. It was grown commercially from 1747 to 1800 and was second only to rice in export value. Carolina indigo was the fifth most valuable commodity exported by Britain’s mainland colonies and was England’s primary source of blue dye in the late-colonial era.

South Carolina experimented with indigo production as early as the 1670s but could not compete with superior dyes produced in the West Indies. Cultivating and processing the plant was complex, and planters found other commodities more reliable and easier to produce. Indigo was reintroduced in the 1740s during King George’s War (1739–1748), which disrupted the established rice trade by inflating insurance and shipping charges and also cut off Britain’s supply of indigo from the French West Indies. In South Carolina, Eliza Lucas Pinckney and Andrew Deveaux experimented with cultivation in the 1730s and 1740s. Pinckney’s husband, Charles, printed articles in the Charleston Gazette promoting indigo. In London colonial agent James Crokatt persuaded Parliament in 1749 to subsidize Carolina indigo production by placing a bounty of six pence per pound on the dye.

In addition to economic motives, indigo production also succeeded because it fit within the existing agricultural economy. The crop could be grown on land not suited for rice and tended by slaves, so planters and farmers already committed to plantation agriculture did not have to reconfigure their land and labor. In 1747, 138,300 pounds of dye, worth £16,803 sterling, were exported to England. The amount and value of indigo exports increased in subsequent years, peaking in 1775 with a total of 1,122,200 pounds, valued at £242,395 sterling. England received almost all Carolina indigo exports, although by the 1760s a small percentage was being shipped to northern colonies.

Two varieties of indigo were native to Carolina, Indigofera Carolinians and Indigofera Lespotsepala, but neither produced a reputable dye. Planters preferred either Indigofera Tinctoria or “Guatemala” indigo, a hearty variety that grew well in a range of soil types, or Indigofera Anil or “French” indigo, a more delicate variety best suited for rich black soil. Prices paid for the dye varied with quality. In general dye from French or Spanish colonies sold for more than Carolina indigo, whose reputation for quality was less favorable. The cycle of planting, processing, and marketing indigo began in March, when the fields were prepared for sowing. Planting began in early April, with a first harvest in July and often a second harvest in August or September. After cutting, the plant was carried to the processing site, a work area generally shaded by a thatched roof. Specialized equipment included three graduated vats set next to each other, in which the plants would be converted to dye. The conversion involved soaking the plants in the first vat, beating the indigo-soaked water in the second vat until thickened grains formed, then draining away that water into the third vat. The thickened mud that settled to the bottom of the second vat was the indigo paste, which was dried, cut into squares, packed in barrels, and shipped to market during the winter months. Slaves were responsible for most of South Carolina’s indigo production. Field slaves planted, weeded, and harvested the crop, and skilled “indigo slaves” worked to convert the plant to dye. Slaves who understood the art of processing the dye had greater value, as an entire year’s product depended on the talents of the indigo maker.

Carolina indigo was grown in a variety of locations and in a number of ways. In the parishes south of Charleston, most indigo planters grew the weed in combination with rice, as a “second staple.” Planters growing indigo closer to the city were split, with roughly half growing rice and indigo and half growing only indigo. North of Charleston, most planters focused solely on indigo. By the 1760s production expanded from the lowcountry to the interior. Indigo was especially important in Williamsburg Township, where the soil was ideal and the crop was an important part of the local economy. By the 1770s, some indigo was also produced in Orangeburg and Fredericksburg Townships.

The Revolutionary War disrupted production, although the Continental army used Carolina indigo to dye some of its uniforms. Production appeared to recover after the war, as 907,258 pounds of dye were exported in 1787. But indigo exports declined sharply in the 1790s. No longer part of the British Empire, South Carolina indigo growers lost their bounty and market as England turned to India to supply its indigo demand. Carolina planters soon after turned their attention to cotton, another crop that fit neatly into the plantation economy. Indigo was produced and used locally throughout the nineteenth century, but by 1802 it was no longer listed among Carolina’s exports.

Chaplin, Joyce E. An Anxious Pursuit: Agricultural Innovation and Modernity in the Lower South, 1730–1815. Chapel Hill: University of North Carolina Press, 1993.

Coon, David L. “Eliza Lucas Pinckney and the Reintroduction of Indigo Culture in South Carolina.” Journal of Southern History 42 (February 1976): 61–76.

Jelatis, Virginia. “Tangled Up in Blue: Indigo Culture and Economy in South Carolina, 1747–1800.” Ph.D. diss., University of Minnesota, 1999. Sharrer, G. Terry. “The Indigo Bonanza in South Carolina, 1740–1790.”

Technology and Culture 12 (July 1971): 447–55.
———. “Indigo in Carolina, 1671–1796.” South Carolina Historical Magazine 72 (April 1971): 94–103.
Winberry, John J. “Reputation of South Carolina Indigo.” South Carolina Historical Magazine 80 (July 1979): 242–50.

Why Indigo?

By Geoffrey von Maltzahn

We here at Indigo have been getting this question a lot over the past few weeks. As a company dedicated to harnessing nature to help feed the planet, some are curious about how “Indigo” aligns with our mission.

In fact, Indigofera, the crop genus from which indigo is derived, has a rich agricultural history – one that embodies our ambitious goals and values as we strive to help improve farming and our foods. This history resonated with us, and elements of our own research also pointed us to the name. We’ll get to that, but first, what exactly is indigo?

Indigo is a legume with symbiotic nitrogen-fixing bacteria in structures called root nodules. Legumes need little or no nitrogen fertilizer in order to provide high yields for the grower, and play a key role in crop rotation, which helps reduce soil erosion, and improve crop yield. This relationship between nitrogen-fixing bacteria and plants is a hallmark example of plant microbiome benefits, and also the tip of the iceberg.

Of course, indigo is most well known as a natural blue dye – a special and rare color in biology – in textiles, derived mostly from two of the over 300 species of the Indigofera genus: Indigofera tinctoria (native to India and Asia) and Indigofera suffruticosa (native to South and Central America). It was used in ancient Asia and Europe to stain clothes and textiles, by the Aztecs to darken their hair and the Mayans to produce azure paint for works of art.

It holds a special place in U.S. history as well, as one of the first agricultural crops grown in this country. By the American Revolution, domestically produced Indigo was such a commodity that it was known as “Blue Gold.” Growers had discovered that small cubes of indigo were more profitable and easier to ship and defend than bulky bags of rice. Cubes could be used in place of paper currency (valued at roughly $2 per pound), and made up 35% of all exports to England.

During our process of studying plant microbiomes across hundreds of plant species and over 40,000 endosymbionts, we learned quite a bit about the interactions taking place within plants. At the core of our discoveries was the realization that the plant microbiome can greatly shape a plant’s biology and protect them from an array of stresses, including drought, heat, salt, cold, nutrient deficiencies, insects and microbial pathogens.

One of the more fun observations we made was that some of a plant’s pigments can be modified, produced and influenced by more than just the plant’s biology. Specifically, certain plant microbes could help create the color indigo. This happened when we observed that certain microbes can produce Indican, a colorless compound which releases glucose and indoxyl that, when oxidized, creates the color indigo. Other plant microbes could oxidize indican to reveal the color directly, revealing bright blue colonies of plant microbes in our labs.

This observation that a common plant pigment can be influenced by the plant microbiome is thematic of our broader story—that the plant microbiome plays extraordinary roles in the biology we’d previously associated with plants.

Also, just as blue is a rare color in biology, we have a special opportunity of our own: to be a leader of a new kind of agriculture – one that is both increasingly natural and scalable. We’re striving to be the first ag tech company to serve the needs of both farmers and consumers and to increase yield and grower profitability while making vital, sustainable changes to how our food is grown. We look forward to sharing more about our science, our team and our vision for better agriculture with you.

Indigo in the Early Modern World

by Anne Mattson

The color indigo, often associated with political power or religious ritual, has held a significant place in many world civilizations for thousands of years. In the excavation of Thebes an indigo garment dating from c. 2500 B.C. was found, for example — furthermore, the Hindu god Krishna is most often depicted in blue,1 human sacrifices were often painted blue in ancient Mayan culture,2 and the Virgin Mary is regularly imagined draped in blue clothes in Christian art.

The indigo dye comes from a leguminous plant of the Indigofera genus, of which over three hundred species have been identified. Only two species are named frequently in the commercial history of the dye, namely: indigofera tinctoria (native to India and Asia) and indigofera suffructiosa (native to South and Central America).3 Indigo plants have a single semi-wood stem, dark green leaves that are oval-shaped in most species, and clusters of red flowers that look like butterflies and turn into peapods. The plants can grow from two to six feet in height and the dye is obtained mainly from the leaves through a process of fermentation.4

The dye is first mentioned in a written source for Western Europe in the histories of Herodotus (writing around 450 B.C.), who described its use in the Mediterranean area.5 It was at the time of the Crusades, however, that indigo became one of the valued “spices” that Italian merchants acquired in Cyprus, Alexandria and Baghdad. These cities were themselves end-points for caravans from the Far East. But the trade in indigo dye only became a commercial force after 1498 with the opening of the sea route to India.6 This is not to say that Europeans had no other way of obtaining deep blue dye. The woad plant, native to northern Italy, southern France, and parts of England and Germany, yielded indigo-colored dye from its leaves, but it was inferior to that obtained from the indigo plant. Quite naturally, the woad-growers of Europe (both peasants and princes) sought to protect their industry against the influx of affordable indigo in the Sixteenth Century. In 1598 indigo was prohibited in France and parts of Germany, and dyers had to swear, often on the pain of death, that they would not use that dye.7 Nevertheless, in the Seventeenth Century indigo became one of the chief articles of trade of both the Dutch and the British East India Companies. Dauril Alden argues that, in fact, the indigo supplies in India were not sufficient to meet the European demand in the Seventeenth Century and that is why indigo cultivation was taken up in the New World as well.8

Beauvais-Raseau, L’Art de l’Indigotier. Paris: L.F. Delatour, 1770.

An indigenous variety of indigo began to be cultivated by Spanish overseers on the plantations of Honduras and the Pacific slopes of Central America in the 1560s. The indigo plant was known to early Guatemalan colonialists by the Nahuatl word xiquilite, and the dye was known to contemporaries as “Guatemalan Indigo.”9 M. De Beauvais Raseau, writing about indigo cultivation in the Eighteenth Century, stated that the Native Americans also knew about extracting dye from the plant. They called it “Tlauhoylimihuitl” and used it to darken their hair.10 It seems that indigo production continued to increase throughout the Seventeenth Century in the New World. The French colony of Saint Domingo eventually became the major producer of indigo, and this dye was also of the best quality. The English gained their first indigo-producing colony in this part of the world in 1655 when they captured Jamaica.11 However, it is unclear how important New World indigo was in the worldwide indigo market, as prices fluctuated and so did production numbers. By 1740 sugar had replaced indigo as the main crop of Jamaica, but, on the other hand, this was also the beginning of the indigo boom in South Carolina.12

Beauvais-Raseau, L’Art de l’Indigotier. Paris: L.F. Delatour, 1770.

It seems that “Guatemalan indigo” did not enjoy as high a reputation in Europe as indigo from Asian countries. In 1746, when “A Friend to Carolina” wrote his tract encouraging the cultivation of indigo in South Carolina he emphasized the necessity of establishing a superior product: “All Kinds are better or worse, as they are neat or pure; for those who make it in America, often maliciously mix it with Sand and Dirt, but the Cheat is easily discovered; as Indigo that is fine and pure will burn like Wax, and, when burnt, the Earth or Sand will remain.”13 He pointed out that in the Americas indigo dye was often made with the stems and branches of the plant instead of just with the leaves. He felt that this too might be detrimental to its quality — “But one ought to have the Leisure and Patience of the Indians, to undertake such a Work , and have Workmen as cheap as they are in that Country.”14

Raseau, who was captain of the militia on Saint Domingo prior to 1770, discusses the history of indigo in all the regions of the world where it could be grown. He gives various methods that were employed for extracting the dye and then goes into greater detail on indigo production in South and Central America. His wonderful little book contains diagrams of the plants, the process of making indigo dye, as well as the ideal plantation.15 Indigo plantations did not require much labor except during July, August and September when the plants were cut, fermented and the dye was extracted. Because it was thought that the Indians were particularly susceptible to the diseases that bred around the fermentation vats, plantation owners claimed that they did most of the field work, while Black slaves extracted the dye. In reality, the division of labor was probably not so strict — particularly since Black slaves were in relatively short supply and were often more expensive to hire than the Indians.16

Beauvais-Raseau, L’Art de l’Indigotier. Paris: L.F. Delatour, 1770.

Finally, I would like to describe the extraction of the dye through the eyes of John Stedman in his Narrative of five years’ expedition. Stedman was invited to view the process of making indigo dye at the plantation of the governor of Surinam and he gives the following account of it:

When all of the verdure is cut off, the whole crop is tied in bunches, and put into a very large tub with water, covered over with very heavy logs of wood by way of pressers: thus kept, it begins to ferment; in less than 18 hours the water seems to boil, and becomes of a violet or garter blue colour, extracting all the grain or colouring matter from the plant; in this situation the liquor is drawn off into another tub, which is something less, when the remaining trash is carefully picked up and thrown away; and the very noxious smell of this refuse it is that occasions the peculiar unhealthiness which is always incident to this business. Being now in the second tub, the mash is agitated by paddles17 adapted for the purpose, till by a skillful maceration all the grain separates from the water, the first sinking like mud to the bottom, while the latter appears clear and transparent on the surface: this water, being carefully removed till near the coloured mass, the remaining liquor is drawn off into a third tub, to let what indigo it may contain also settle in the bottom; after which, the last drops of water here being also removed, the sediment or indigo is put into proper vessels to dry, where being divested of its last remaining moisture, and formed into small, round, and oblong square pieces, it is become a beautiful dark blue, and fit for exportation. The best indigo ought to be light, hard, and sparkling.18

These blocks of indigo were what was so highly prized on the European market. It was only in 1897 that the German firm BASF produced an Ersatz form of indigo dye that finally took the place of the natural product.19

Notes

1. Gösta Sandberg, Indigo Textiles: Technique and History (London: A & C Black, 1989), 14.
2. Murdo J. MacLeod, Spanish Central America. A Socioeconomic History (Berkeley, Los Angeles, London: University of California Press, 1973), 176.
3. Sandberg, Indigo Textiles, 19; MacLeod, Spanish Central America, 178; see also Virginia Jelatis, “Indigo Production in the Lower South: 1740-1775),” (M. A. Thesis, University of Minnesota, 1993), 12-13 — though she is slightly confused on these points.
4. Dauril Alden, “The Growth and Decline of Indigo Production in Colonial Brazil: A Study in Comparative Economic History,” Journal of Economic History 25 (1965), 36; and Sandberg, Indigo Textiles, 19.
5. Jelatis, “Indigo Production,” 12.
6. Alden, “Growth and Decline,” 37.
7. Alden, “Growth and Decline,” 37-38; and Sandberg, Indigo Textiles, 27.
8. Alden, “Growth and Decline,” 39.
9. Alden, “Growth and Decline,” 40.
10. “Les Naturels de l’Amerique, font avec ses feuilles, une teinture qu’ils appellent Tlauhoylimihuitl, dont ils se servent pour noicir leurs cheveux.” M. De Beauvais Raseau, L’Art de L’Ingotier (France: L.F. Delatour, 1770), 29.
11. Alden, “Growth and Decline,” 41.
12. Jelatis, “Indigo Production,” 17-18.
13. “A Friend to Carolina,” Observations concerning Indigo and Cochineal (London: 1746), 21.
14. “A Friend to Carolina,” Observations, 15.
15. Raseau, L’Art de L’Ingotier plates at the back of the book.
16. MacLeod, Spanish Central America, 184-86.
17. Raseau refers to this part of the process as being something like to the churning of butter in his own country: L’Art de L’Ingotier, 22.
18. John Gabriel Stedman, Narrative, of a five years’ expedition, Guiana, on the wild coast of South America vol. 2 (London: J. Johnson, St. Paul’s Church Yard and J. Edwards, Pall Mall, 1796), 303-4.
19. Sandberg, Indigo Textiles, 35.

The Color Indigo

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The color of intuition, perception and the higher mind

The color indigo is the color of intuition and perception and is helpful in opening the third eye. It promotes deep concentration during times of introspection and meditation, helping you achieve deeper levels of consciousness. It is a color which relates to the “New Age” – the ability to use the Higher Mind to see beyond the normal senses with great powers of perception. It relies on intuition rather than gut feeling.

Indigo is a deep midnight blue. It is a combination of deep blue and violet and holds the attributes of both these colors.

Service to humanity is one of the strengths of the color indigo. Powerful and dignified, indigo conveys integrity and deep sincerity.

The color meaning of indigo reflects great devotion, wisdom and justice along with fairness and impartiality. It is a defender of people’s rights to the end.

Structure creates identity and meaning for indigo. In fact an indigo person cannot function without structure – it throws them right off balance. Organization is very important to them and they can be quite inflexible when it comes to order in their lives.

Indigo loves rituals and traditions, religion and the institutional system, conforming to things that have worked in the past while planning for the future.

Indigo stimulates right brain or creative activity and helps with spatial skills. It is a dramatic color relating to the world of the theater, which, during times of stress becomes the drama queen, making a mountain out of a molehill!

The negative color meaning of indigo relates to fanaticism and addiction. Its addiction encompasses everything from a need for recognized qualifications to a need for illegal drugs, from the workaholic to the religious fanatic.

Indigo can be narrow-minded, intolerant and prejudiced.

If your favorite color is indigo, it will reflect in your personality! Personality color indigo will give you more information on this.

If you are thinking of using indigo in a business application, read about the meanings of colors in business.

Positive and Negative Traits of Indigo

Positive keywords include integrity and sincerity, structure and regulations, highly responsible, idealism, obedience, highly intuitive, practical visionary, faithful, devotion to the truth and selflessness.

Negative keywords include being fanatical, judgmental, impractical, intolerant and inconsiderate, depressed, fearful, self-righteous, a conformist, addictive, bigoted and avoiding conflict.

The Color Indigo Represents

Intuition: use it to assist in accessing intuitive abilities – it is the first step to higher spiritual knowledge

Integrity: and deep sincerity are qualities of indigo

Structure and Order: a good colour to use in restructuring aspects of your life or business

Wisdom: an inner knowingness and awareness – spiritual wisdom rather than the wisdom of the intellect

Effects of The Color Indigo

Introspection: promotes deep concentration during times of introspection and meditation – can lead to feelings of being spaced out.

Idealistic: an ability to plan for the future.

Addiction: can support an addictive personality into maintaining their addictions – don’t use it if you are trying to overcome an addiction – it is associated with the religious fanatic – the colour of the workaholic who thinks they are indispensable – can also be related to those who are addicted to getting qualifications.

The Dramatist: relates to the acting profession – can cause people to ‘make a mountain out of a molehill’.

Conformity: a love of ritual – conformity to the things that have worked in the past, not just for the sake of conforming.

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People say that a picture is worth a thousand words, so let’s take a look at the two colours in comparison (there are various shades of purple and violet, and the following picture shows some of the more common ones):

So, purple is more reddish and saturated, while violet is more bluish and less saturated. Case closed, right?

There is more in it than the eyes can see (quite literally). To understand the difference, we have to take a look at how our eyes work first. The electromagnetic spectrum is a continuous range of wavelengths, only a tiny part of which is visible to humans:

We see neither the ultraviolet wavelengths and shorter, nor the infrared wavelengths and longer. How do we see the rest? We have three types of colour-sensitive cells in our eyes, so-called cones. The cones don’t perceive just a single wavelength; they are activated by a whole range of wavelengths, and the signals received from the cones are then processed by the brain in such a way that every colour can be thought of as composed of three different elementary signals.

The following picture shows approximately how the brain perceives different spectral colours (the higher the curve, the higher the intensity of the elementary signal the brain receives):

Note that this chart does not show the spectral properties of the cones themselves (but they look similar). It represents the CIE 1931 colour space, which, simply put, corresponds to the signals after they have been processed by the brain.

For example, when you see monochromatic (pure) red light on the very right side of the spectrum, only the “red” signal path is activated, which tells your brain to create the impression of red. On the other hand, when you see pure green light (in the middle), both “green” and “red” paths are activated, but your brain knows that “a lot of green activation and a bit less red activation” is in fact just a pure green colour, which is what you see.

When a mixture of photons that have different wavelengths hits the retina (creating a ratio of red, green, and blue activation different from any spectral colour), the brain will perceive it as an entirely different colour. For example, there is no white wavelength. What we perceive as “white” is in fact just a mixture of many different spectral colours.

What happens when violet light hits the retina?

The “red” signal path has an interesting additional property. As you can see above, it has a small bump of activation around the short-wavelength (violet) end of the visible spectrum. When violet light hits the retina, both the “blue” path and (much less) the “red” path are activated. The brain interprets this kind of input in a specific way, which we call “violet”.

It is worth noting that the pigment in the “green” cones themselves also has a small peak of absorption around violet wavelengths, but the brain seems to ignore it (it is not possible to simulate the perception of violet by a combination of green and blue light).

Purple is not a spectral colour

As we noted before, many colours we can see are not in the visible spectrum. When you see an object, typically a mixture of different wavelengths reaches your retina, which causes the cones to be activated at a ratio not achievable by a spectral colour.

Our brains are very good at interpreting this mixture (it would be silly to simply throw away a part of the incoming information and make everything look like the closest spectral colour), and, as a result, we are able to see several million different colours, most of which are not present in the spectrum.

As we noted at the beginning of the article, purple looks more “reddish” than violet, and that’s absolutely correct. Purple is formed by mixing red and blue in a ratio close to 1:1, whereas violet is perceived by your eyes as containing more blue than red.

However, as you can see from the picture above, no spectral colour activates the “blue” path and the “red” path at the ratio of 1:1 without also stimulating the “green” path. In other words purple is not a spectral colour. You can have a source of monochromatic violet light (i.e. a source producing just a single wavelength), but everything that looks purple must emit both red and blue light.

Purple and violet look similar only to humans

To us, humans, purple looks like a more saturated shade of violet, but violet objects in nature are fundamentally different from purple ones. Purple objects are “red and blue at the same time”, whereas violet objects are… just violet.

If you take a look at the distance between violet and blue in the picture of the spectrum above, it is about the same as the distance between green and orange. Purple is a mixture of red (which is at the opposite side of the spectrum than violet) and blue (which is relatively far from violet), so it is, in terms of wavelengths, a completely different colour.

The reason why purple and violet look similar to us is because they stimulate our cones in a similar way, but most other animals don’t share the same types of cones and “post-processing”. This means that to other animals, purple and violet may look completely different!

Now imagine a violet flower petal with a purple pattern on it. Depending on the particular shades, this pattern might be completely invisible to us, while many other animals could see it as clearly as we can see an orange pattern on green background. Even common consumer cameras wouldn’t help us; they are designed to capture the same red-green-blue information as our eyes do, so even taking a photo of the petal and editing it in Photoshop would not uncover the pattern. Quite fascinating, isn’t it?

Natural Indigo dye

Indigo and Natural Indigo Dye

1. Dyeing with Indigo
Indigo is light-fast and does not require fibre to be mordanted beforehand, making it easier for you to dye cotton than most other natural dyes.
Indigo is also ideal for use in batik; unlike many other natural dyes that require a high temperature, indigo works at low temperatures and does not melt batik wax. It works quickly and you can get blue fabric after just 10 minutes in the indigo vat. Speed is useful for tie dye and shibori as there is not enough time for the dye to spoil the pattern by penetrating under the ties.
Using just indigo and a resist technique such as shibori or batik, you can create countless blue and white patterns with timeless appeal. Indigo, however, is a base for many other colours. It is almost essential for good greens and blacks and you can produce a wide range of greens by overdyeing indigo with yellow dyes such as weld or Persian berry. For attractive violets, purples and mauves, overdye it with madder or cochineal. Very dark indigo overdyed with madder and sometimes gallnut or iron produces good blacks.

Buy Indigo cakes!

Indigo is sold as a dark blue crystalline powder and is not soluble in either water or alcohol. First you need to make it soluble in an alkaline vat where oxygen has been removed either by fermentation or with a suitable chemical. You then dip your fibre in the vat and the soluble indigo combines with the fibre. When you expose the fibre to oxygen in the air you will see it gradually change colour from pale yellow to green and then finally to blue, as the indigo dye reverts to its insoluble blue form. Seeing the colour develop in the air must have looked like magic to many early cultures, and this change in colour can easily get you hooked on dyeing blues (read more on recipes for indigo dyeing).
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2. Types of Indigo Plants
Much of the world has native plants that produce indigo and more than fifty different species of plants produce indigo in usable quantities. Indigo-bearing plants come from families as diverse as the bean family (leguminosae), cabbage family (cruciferae) and rhubarb family (polygonaceae). Examples of indigo-bearing plants include several species of Indigofera, Japanese indigo (Persicaria tinctoria), woad (Isatis tinctoria), dyer’s oleander (Wrightia), Strobilanthes and Marsdenia. You can read in more detail about these and other sources of indigo in an excellent book by Dominique Cardon, “Natural Dyes, sources, tradition, technology and science”.
Most natural indigo dye for sale comes from the leaves of Indigofera tinctoria. This plant is tender to frost and grows best in the tropics, thriving in hot and humid places with fertile soil. It is commercially grown in India, El Salvador, Vietnam and some other countries. It is an annual or perennial, 2 m tall, and has compound leaves with many oblong leaflets. The leaves close at night and spread open again at dawn (read more on growing indigo).
As much as 20 tonnes of leaves are needed to produce just 45 kilos of pigment and unlike other natural dyes, indigo is not present in the plant. Only the chemical precursor of indigo is present and you need to process the leaves to produce the indigo powder. Although you need to follow the instructions carefully, it is not difficult to extract your own indigo if you harvest the leaves at the right time (read more on indigo extraction).

3. Indigo History
Indigo is an ancient dye and there is evidence for the use of indigo from woad or Indigofera from at least the third millennium BC, and possibly much earlier for woad (read more about the history of indigo).
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4. Natural Indigo versus Synthetic Indigo
Although the chemical formula for natural and synthetic indigo is the same, synthetic indigo is almost pure indigotin. Natural indigo has a high proportion of impurities such as indirubins, that give beautiful colour variations. Like fine wines, the blue you get depends on where the indigo was grown and the weather at the time. Synthetic indigo on the other hand, produces an even blue that never varies.
Natural indigo is a sustainable dye; after the pigment has been extracted the plant residue can be composted and used as a fertiliser and the water reused to irrigate crops. Natural indigo can often be traced to its country of origin, and even to the farm where it was produced. In buying it, you will be helping to give sustainable employment to rural population in developing countries. Synthetic indigo on the other hand is extracted from petrochemicals and its manufacture produces hazardous waste. By using natural indigo, you will be helping the environment and reducing the use of petrochemicals.
Natural indigo is the ideal blue dye to use on handmade textiles and on natural fibres; it may cost a little more than synthetic indigo, but the main cost of handmade items is time. Natural indigo is also essential for living history research, and for historic re-enactments. This may seem obvious, but if you want to use natural dyes, you need to use natural indigo rather than synthetic. Synthetic indigo is not a natural dye. Sometimes dyers may be unaware that they are in fact using synthetic indigo, as some shops don’t always make it clear what type of indigo they are selling. If in doubt, check with your supplier!

indigo chemistry

1. Why use Indigo?
2. Mayan Indigo from El Salvador – NEW
3. Growing & Harvesting Indigo
4. Dyeing with natural Indigo
5. Dyeing with Indigo crystals
6. Gallery of indigo-dyed cotton samples
7. History of Indigo
8. Indigo Chemistry

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Indigo

Background

Indigo, or indigotin, is a dyestuff originally extracted from the varieties of the indigo and woad plants. Indigo was known throughout the ancient world for its ability to color fabrics a deep blue. Egyptian artifacts suggest that indigo was employed as early as 1600 B.C. and it has been found in Africa, India, Indonesia, and China.

The dye imparts a brilliant blue hue to fabric. In the dying process, cotton and linen threads are usually soaked and dried 15-20 times. By comparison, silk threads must be died over 40 times. After dying, the yarn may be sun dried to deepen the color. Indigo is unique in its ability to impart surface color while only partially penetrating fibers. When yarn died with indigo is untwisted, it can be seen that the inner layers remain uncolored. The dye also fades to give a characteristic wom look and for this reason it is commonly used to color denim. Originally extracted from plants, today indigo is synthetically produced on an industrial scale. It is most commonly sold as either a 100% powder or as a 20% solution. Through the early 1990s, indigo prices ranged near $44/lb ($20/kg).

History

The name indigo comes from the Roman term indicum, which means a product of India. This is somewhat of a misnomer since the plant is grown in many areas of the world, including Asia, Java, Japan, and Central America. Another ancient term for the dye is nil from which the Arabic term for blue, al-nil, is derived. The English word aniline comes from the same source.

The dye can be extracted from several plants, but historically the indigo plant was the most commonly used because it is was more widely available. It belongs to the legume family and over three hundred species have been identified. Indigo tinctoria and I. suifruticosa are the most common. In ancient times, indigo was a precious commodity because plant leaves contain only about small amount of the dye (about 2-4%). Therefore, a large number of plants are required to produce a significant quantity of dye. Indigo plantations were founded in many parts of the world to ensure a controlled supply.

Demand for indigo dramatically increased during the industrial revolution, in part due to the popularity of Levi Strauss’s blue denim jeans. The natural extraction process was expensive and could not produce the mass quantities required for the burgeoning garment industry. So chemists began searching for synthetic methods of producing the dye. In 1883 Adolf von Baeyer (of Baeyer aspirin fame) researched indigo’s chemical structure. He found that he could treat omega-bromoacetanilide with an alkali (a substance that is high in pH) to produce oxindole. Later, based on this observation, K. Heumann identified a synthesis pathway to produce indigo. Within 14 years their work resulted in the first commercial production of the synthetic dye. In 1905 Baeyer was awarded the Nobel Prize for his discovery.

At the end of the 1990s, the German based company BASF AG was the world’s leading producer, accounting for nearly 50% of all indigo dyestuffs sold. In recent years, the synthetic process used to produce indigo has come under scrutiny because of the harsh chemicals involved. New, more environmentally responsible methods are being sought by manufacturers.

Raw Materials

The raw materials used in the natural production of indigo are leaves from a variety of plant species including indigo, woad, and polygonum. Only the leaves are used since they contain the greatest concentration of dye molecules. In the synthetic process, a number of chemicals are employed as described below.

The Manufacturing Process

Natural extraction

  • 1 Plant extraction of indigo requires several steps because the dye itself does not actually exist in nature. The chemical found in plant leaves is really indican, a precursor to indigo. The ancient process to extract indican from plant leaves and convert it to indigo has remained unchanged for thousands of years. In this process, a series of tanks are arranged in a step wise fashion. The upper-most tank is a fermentation vessel into which the freshly cut plants are placed. An enzyme known as indimulsin is added to hydrolyze, or break down, the indican into indoxyl and glucose. During this process carbon dioxide is given off and the broth in the tank turns a murky yellow.
  • 2 After about 14 hours, the resulting liquid is drained into a second tank. Here, the indoxyl-rich mixture is stirred with paddles to mix it with air. This allows the air to oxidize the indoxyl to indigotin, which settles to the bottom of the tank. The upper layer of liquid is siphoned away and the settled pigment is transferred to a third tank where it is heated to stop the fermentation process. The resultant mixture is filtered to remove impurities and dried to form a thick paste.

    Historically, the Japanese have used another method which involves extracting indigo from the polygonum plant. In this process the plant is mixed with wheat husk powder, limestone powder, lye ash, and sake. The mixture is allowed to ferment for about one week to form the dye pigment which is called sukumo.

Synthetic production

  • 3 A variety of synthetic chemical processes have been used to produce indigo. All these processes involve combining a series of chemical reactants under controlled conditions. The reactants undergo a series of reactions which result in the formation of the indigo molecule. A number of other chemical byproducts are also produced in this reaction.
  • 4 These synthesis reactions are conducted in large stainless steel or glass reaction vessels. These vessels are equipped with jackets to allow steam or cold water to flow around the batch as the reactions progress. Because of the complexity of these chemical processes, the dye is usually made in batch quantities. There are, however, a few methods invented by the Germans for continuous process manufacturing.

Types of reactions

  • 5 The first commercial method of producing indigo was based on Heumann’s work. In this method, N-phenylglycine is treated with alkali to produce indoxyl, which can be converted to indigotin by contact with air. However, the amount of dye yielded by this process is very low. Another, more efficient, synthesis route utilizes anthranilic acid. This process was popular with major manufacturers, such as BASF and Hoechst, for over 30 years. A variation of this method (which has become widely used) involves the reaction of aniline, formaldehyde, and hydrogen cyanide to form phenylglycinonitrile. This material is then hydrolyzed to yield phenylglycine which is then converted to indigotin. Currently, a method which uses sodamide with alkali to convert phenylglycine to indoxyl. Sodamide reacts with excess water, thus lowering the overall reaction temperature from almost 570°F (300°C) to 392°F (200°C). This results in a much more efficient reaction process.

Finishing operations

  • 6 After the chemical reaction process is complete, the finished dye must be washed to remove impurities and then dried. The dried powder can be packed in drums or reconstituted with water to form a 20% solution and filled in pails.

    The chemical symbol for indican, the compound found in the leaves of the indigo plant that is used to make indigo dye.

Quality Control

During indigo manufacture, the reaction process is continuously monitored to ensure the chemicals are combined in the proper ratios. Key elements that must be controlled include the pH (or acid/base quality of the batch), the temperature (which controls the speed of the reaction), and the reaction time (which determines the degree of completion). If any of these variables deviate from specifications, the resulting reaction product can be affected. Typically, poor quality control results in lower yield of the dye, which increases costs for the manufacturer.

To ensure that manufacturers can consistently purchase the same shade of dye, indigo is assigned a Color Index number that defines its shade. It is designated as “CI Natural Blue CI 75780.”

Byproducts/Waste

Indigo production produces a variety of waste products which must be handled carefully. In addition to the reactants described above, there are other reaction side products that are produced along with the indigo. Some of these materials are considered to be hazardous and must be disposed of in accordance with local and federal chemical waste disposal guidelines. These waste chemicals can enter the environment in at least three different ways. The first is during the actual manufacture of the molecule. The second is when the dye is applied to the yarn, and the third is when the dye is eluted into the wash water during the initial stonewashing or wet processing of the fabric. This last route typically occurs during the production of denim fabric.

The Future

Much of the need for indigo is being met with other types of blue dyes and today most of the indigo used by the world is made out-side the United States. Researchers are concentrating on new methods of indigo manufacture that are more environmentally friendly. One promising future method involves using biocatalysts in the dye reaction process. Indigo dye may be one of the first high-volume chemicals made through a biological route. Genencor International, of Rochester New York, is evaluating a process to produce indigo using biotechnology. According to Charles T. Goodhue, Genencor’s Program Director/Biocatalysis Research and Development, indigo produced by this method is chemically the same as the regular synthetic dye and behaves identically in dyeing tests. However, at this time the technology is expensive and production costs could be prohibitive. Genencor is seeking a major market partner to work with them in the development of this new technology.

Manufacturers who use indigo in dying operations are also seeking to improve their use of the dye. For example, Burlington’s Denim Division introduced a technology in 1994 they call “Stone Free,” which allows indigo dye in the fabric to break down 50% faster in the stonewash cycle. Compared to traditional methods of stonewashing fabric dyed with indigo, their new process uses few, if any, pumice stones which help give the fabric its faded look. Therefore, pumice stone handling and storage costs are reduced, along with time required to separate pumice from garments after stonewashing. It also uses much less bleach. Therefore, this new process not only reduces garment damage, but also reduces waste produced by the stones and bleach.

Where to Learn More

Books

Periodicals

McCurry, John. “Burlington Debuts Stone Free Denim.” Textile World 144, no.3 (March 1994): 120-123.

Rotman, David, and Emma Chynoweth. “The Quest for Reduced Emissions, Greener Processes.” Chemical Week 153, no.1 (July 7,1993): 117.

— Randy Schueller

The Process: Indigo from Plant to Paste

Though the process of turning green leaves into brilliant blue dye through fermentation has been practiced for thousands of years, it still feels magical. Most natural dye colors are derived from bark, berries, or leaves that can be boiled down and dyed with—but the process of making blue dye is much more difficult.

Every community—places like Mexico, Nigeria, and Japan—has its own spiritual rituals, recipes, and techniques for creating natural indigo dye. In India, the birthplace of indigo, dye paste is dried into cakes for easy transportation and trade. The synthetic dyes which enable today’s plentiful supply of commercial denim and tie-dyed products replicate the look of natural dye almost exactly. Since Levi Strauss created his first pair of workwear blue jeans with indigo in 1873, though, the process has changed remarkably.

As a freelance fashion designer, I’ve designed denim apparel for brands who have the manufacturing capabilities of washing, distressing, and styling denim for mass market. But when I first witnessed the wondrous natural process of making indigo from plant to paste at a small studio in Thailand, I fell in love with the traditional process and the brilliant color it produces.

This is the real deal. I have returned again and again to Studio Naenna in Chiang Mai to learn from esteemed author and artist Patricia Cheesman who has been practicing this art form for 25 years.

The Natural Indigo Dye Process

Here’s the 10 step process of making natural indigo dye as learned from Patricia and the team at Studio Naenna.

Previous

Step 1: Harvesting the indigo

The indigiferna tinctoria was planted during Thailand’s rainy season in June. By September or October, the plants are ready to be pruned and used for making dye.

Step 2: Bundling

We bundle the small leaf Indiofera tinctoria leaves together using stems as ties. The larger leaf varieties of indigo like Strobilanthes flaccidifolius can go straight into the bins.

Step 3: Soaking

Water is added to the bins. Heavy stones are used to press the color from the leaves during an overnight soak. The covered bins need to sit for about 24 hours, depending on the weather.

Step 3 (After 24 Hours…)

Voilà! Like magic, the water has fermented overnight and turned blue.

Step 4: Removing the bundles

The bundles are drained and removed. The plants are used for fertilizer.

Step 5: Adding lime

2% builders lime Ca(OH)2 is gently mixed into the colored water.

Step 6: The Beating Process (Part One)

The water and lime must be beaten for about 20 minutes – dipping the bowl in and out – oxidizing the mixture. The water changes from murky green to peacock blue to a frothy navy color.

Step 6: The Beating Process (Part Two)

When the mixture turns frothy and navy-colored it is almost ready. Patricia has an ear for the “sshhwaa” sound of bubbles breaking that is the signal to stop beating.

Step 7: Collecting the paste (Part One)

Patricia prepares the cloth for paste collection.

Step 7: Collecting the paste (Part Two)

After the indigo paste precipitated to the bottom of the bin overnight, we carefully removed the brown water from the top. The paste is then collected by pouring it over mesh (collecting debris) then though a fine cotton cloth.

Step 7: Collecting the paste (Part Three)

This is natural indigo paste, which can be stored in plastic bins for one to two years and used for dyeing later. Notice the beautiful variations in color.

Step 8: Preparing the vat

Dyeing takes place in the green form of indigo which is known, confusingly, as white indigo. The paste is mixed with ash water, fruit sugars or rice whiskey, and left to ferment. After a few days of stirring and adding sugars, it’s ready to dye with. Keeping an indigo vat alive is tricky, but Patricia has continually nurtured this vat for 25 years.

Step 9: Tie Dye and Shibori

Tie dye and Japanese Shibori are created by tying, rolling, stitching, and folding white cloth before dyeing. The tied-up portions of cloth remain white while the exposed areas turn blue in the indigo vat.

Step 10: Dyeing (Part One)

Cloth coming out of the white indigo vat has a green appearance but quickly turns blue with oxidation. Creating a light or a dark blue cloth requires multiple dips as indigo platelets are layered onto the cloth or yarn.

Step 10: Dyeing (Part Two)

Different shades of indigo after one or multiple dips in the vat.

The Finished Product

Mindy the Indigo Dog models a tie dyed handkerchief!

To Learn More…

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I first met Sarah Bellos of Stony Creek Colors in 2016 when she spoke at the Growing Color Symposium at the NC Arboretum in Asheville. She presented her vision for growing and extracting indigo in Tennessee. Her goal was to introduce natural indigo to the denim industry, which is currently a huge consumer of synthetic indigo (a serious source of environmental pollution). She was partnering with Tennessee farmers who had previously grown tobacco and planned to process indigo dye locally.

Air drying of traditional burley tobacco in TN Some Tennessee grown tobacco is cured by smoking with wood fire

I must admit that I was somewhat skeptical. The project seemed too big and too optimistic. I didn’t know anyone who had successfully grown indigo dye plants on the scale that she described. Most dye plants are grown for commercial purposes in India or South America, where the price of labor is far less. Indigo was grown in the Southeast coastal regions of South Carolina and Georgia in the 17th and 18th centuries but, to my knowledge, has not been grown commercially in North America since that time.

On a recent visit to Stony Creek near Nashville, TN I was very pleasantly surprised and now believe that they are truly on the way to something successful and very much needed. I’d like to tell you why I believe this.

The first place visited was the “test farm”. I had envisioned a small plot of Persicaria tinctoria but was amazed to find that the test farm was a densely planted, multiple acre farm tract where several strains of Persicaria tinctoria are growing next to the tropical varieties of indigo (Indigofera suffruticosa and Indigofera tinctoria).

Tropical indigo plants (Indigofera suffruticosa), harvested and continuing to grow in foreground, not yet harvested in background Sarah in the test field, where several varieties of indigo are grown Persicaria tinctoria, in bloom

Why grow so many different types of plants? Sarah and her staff are constantly asking questions and testing: Which varieties can be sown directly in the ground? Which need to be started in the greenhouse? Some strains bloom more readily than others (great for seed production but not so good for indigo production). Which plants can be dried for future extraction? What is the indigotin content vs. the biomass of the plants? Which can be harvested most efficiently?

I believe that the Stony Creek team is concluding that there is wisdom in growing more than one variety of indigo. The farmers are currently growing many acres of indigo for pigment extraction. All farms are within a reasonable drive to the factory, as it is necessary to process the indigo leaves quickly.

The next stop was Stony Creek’s lab. Walking in the door I saw that the dye chemist, Summer Arrowood, was pulling leaves from Persicaria tinctoria stems that had been harvested earlier that morning. She was weighing those leaves and recording the leaf-to-stem ratio. Next, individual bags of leaves (from very specific plants in very carefully identified locations at the test farm) were processed to extract the indigo pigment. I sensed that this was part of each day’s work at the lab. The leaves were soaked in hot water, the liquid was pumped into vessels for aeration, the paste was allowed to settle and then filtered. Several hours later, each batch of leaves had produced a small amount of indigo pigment. These were tested, labelled and stored for future reference. They report that their indigo contains 25-35% indigotin which is a very concentrated output.

Vessels for test extractions of pigment. Sarah is holding the piping used for introducing oxygen into the indigo extraction in order to precipitate the pigment. Filtering of test pigment Pigment extracted from test extractions Each sample batch of pigment is carefully labeled for reference Yoshiko Wada, and Summer Arrowood, Stony Creek’s dye chemist, observing the results of TLC, (thin layer chromatography), used to determine whether indigo pigment samples that Yoshiko brought were natural or synthetic. Indigofera suffruticosa seed pods Indigofera tinctoria seed pods Stony Creek is experimenting with extraction from dried plant material in order to extend the production season.

The production factory is located in a county-owned, former tobacco factory and leased by Stony Creek. Here, 20,000 pounds of indigo plant material can be processed in a single batch. The factory is set up with modern equipment, carefully laid out, and efficient. Stony Creek precipitates indigo pigment without the use of lime (calcium hydroxide). When too much lime is used during the process, it will remain in the indigo pigment and skew the weight of any available indigotin. The extraction without lime is one of the reasons the pigment has such high levels of indigotin. The pigment paste is carefully filtered using processes that Stony Creek has developed specifically for indigo.

Truck trailers used for indigo harvest and initial steeping of plants. Water that has been collected from the root and heated in solar tanks is used for extracting the indigo. Stainless tanks are used for aerating the indigo. Stony Creek has recently installed two additional tanks. Plastic tanks are used for settling of the indigo paste. All indigo paste settles to the very bottom of the tanks. The remainder is waste water, that is properly neutralized before discarding.

How has Stony Creek come this far so quickly? Sarah Bellos has an academic background and experience in natural resources management and sustainable agriculture. She is a self-taught natural dyer; she and her sisters operated a dye business for several years under the name Artisan Natural Dyeworks. Stony Creek employs skilled and smart people, who know chemistry, plants, agriculture, and manufacturing. The farmers, who grow the indigo, are benefiting from a cash crop that has the potential to replace the tobacco that grew here for so long. Stony Creek is currently selling indigo paste to denim producers and they are able to test/replicate the warp dyeing process used by the denim industry in their lab. Sarah had a vision to produce natural indigo and they are making it a reality.

This chart says it all!

At a time when some of us are unsure if we are purchasing natural indigo or synthetic indigo (or a mix of both) Stony Creek is a beacon of light. I have used their indigo and it is excellent. Of course I will purchase my indigo from them! I will encourage other dyers to do the same.

Stony Creek is NOT yet set up for visitors. Right now, they need to focus on the work at hand and continue to develop their current products: indigo, black walnut paste extract (that really works!), and a madder extract paste (currently from Rubia tinctorium roots grown in India until their own roots are ready for harvest).

After this year’s indigo harvest they plan to move the lab to the factory location and at some time in the future will be able to offer workshops onsite. I hope that you will consider helping to grow this promising endeavor by trying out their excellent indigo, and other extracts available for order online at their website. Other dye suppliers are also beginning to carry and sell Stony Creek Indigo.

The day we visited the factory, there was no indigo being processed. It had rained the day before and the indigo plants cannot be harvested when wet; this whole process is tied closely to the land. Before we left in the afternoon, the truck and trailer had left for the fields, ready to be loaded with indigo plants early the next morning.

Indigo in the Fabric of Early South Carolina

Indigo—both as a plant and a dye—forms an important chapter in the early history of the South Carolina Lowcountry. Although its memory flourishes today in conversations and artistic expressions, lingering misconceptions have distorted our general understanding about the real story of local indigo. In an effort to help “grow” this colorful conversation, I’ve crafted a series of common questions and factual responses that address some of the most important points of indigo history that every Charlestonian should know.

What is indigo?

Indigo is the name of a large family of deciduous shrubs, identified in modern scientific nomenclature as part of the genus Indigofera. This genus encompasses many hundreds of species of indigo, most of which flourish in tropical areas like India, Africa, and Latin America. Some species are native to subtropical climates, however, and flourish in places like the coastal regions of the American southeast.

Indigo is also the name of an organic blue dye extracted from the leaves a number of plants around the world. For many thousands of years, humans have used this dye to impart a lasting blue color to a wide variety of textiles. From the humble vestments of blue-collar laborers, to royal robes, to tapestries and other artistic expressions, indigo is deeply imbedded in the long history of human culture.

Botanical historians believe that ancient people on the subcontinent of India were the first to domesticate a plant now identified by the scientific name Indigofera tinctoria. The deep blue dye they extracted from its leaves was dried into a powder or small cakes and exported to the east and to the west. Two thousand years ago, the Romans called this product indicum, and that name formed the root of the later English spellings, indico and indigo.

Early trade routes like the Silk Road brought indicum to Medieval Europe, but professional trade guilds actively resisted the introduction of Indian indigo into Europe for many generations. Since ancient times, Europeans had cultivated the woad plant (Isatis tinctoria) to produce a very similar blue dye for textiles, and woad farmers and dyers wanted to protect their traditional trade. As indigo production shifted to the New World colonies in the late sixteenth and early-seventeenth centuries, however, Europeans eventually discovered that indigo was cheaper and more colorfast than woad, and that traditional market declined.

What does indigo have to do with South Carolina history?

Indigo was grown in early South Carolina to produce blue dye that was exported to England for use in the British textile industry. Indigo formed a significant part of the South Carolina economy for approximately fifty years, from the late 1740s to the late 1790s. During that period, indigo (or, more specifically, indigo dyestuff) was South Carolina’s second most valuable export, behind rice.

The cultivation and production of indigo also involved the labor of thousands—perhaps tens of thousands—of people in the South Carolina Lowcountry. For this reason, the cultural memory of indigo is heightened among members of the African-American community along what is now called the Gullah Geechee Cultural Heritage Corridor of South Carolina, Georgia, and Florida.

Why was indigo cultivated in South Carolina?

Early South Carolina planters cultivated indigo to satisfy commercial demand for the dye product in the English (later British) textile industry. This activity was one small part of a much larger mercantile economy. From a mercantile perspective, the entire purpose of the Carolina colony was to produce resources and wealth that would enhance the larger British economy and support the expansion of the British empire. The cultivation of indigo in colonial South Carolina was but a cog in that macroeconomic wheel of fortune that revolved around the hub of London.

As with tobacco in Virginia and sugar cane in the Caribbean, indigo was quite literally a foreign commodity to the early settlers of South Carolina. They did not plant indigo here as an extension of farming traditions back “home.” Textile merchants in eighteenth-century England were certainly familiar with indigo dye, but English farmers had no history of cultivating indigo as a crop. For South Carolinians, the foray into indigo production was a purely speculative venture.

Indigo had no value to the early settlers of South Carolina except as a commodity for export. As a plant, one couldn’t eat it, smoke it, feed it to animals, make it into clothing, or build a house out of it. The process of extracting the dyestuff from the plant was costly, time consuming, and labor intensive. The only motivation for investing time, money, and resources into such undertaking was the promise of profit at a market located more than three thousand miles away. Some of South Carolina’s indigo might have been used to dye textiles locally, but, prior to the nineteenth century, we purchased the vast majority of our textiles directly from England, “dyed in the wool.”

Which species of Indigo were cultivated in early South Carolina?

Three distinct species of indigo were cultivated during the first century of the colony of South Carolina. The first and most logical variety is, of course, the native species of wild indigo now classified as Indigofera caroliniana. This is a subtropical species that is found from southern Virginia to Louisiana along the eastern seaboard and Gulf Coast of North America. Colonists did experiment with it here in the eighteenth century, but they deemed its dyestuff to be inferior—in both color and volume—to that of two imported species.

The ancient Indian species (Indigofera tinctoria) came to early South Carolina through contact with English, French, and Dutch merchants trading across the Atlantic and throughout the Caribbean. Because many French planters cultivated this Indian species in their Caribbean colonies, such as Saint-Domingue (Haiti) on the island of Hispañola, eighteenth-century South Carolinians usually referred to this species as “French” or “Hispañola” indigo.

A species of indigo native to Guatemala (Indigofera suffruticosa) also came to early South Carolina through trans-Atlantic and Caribbean trade networks. This Latin American species was cultivated for centuries by the indigenous Maya people of that region, and Spanish colonists began exporting indigo dye from Guatemala to Europe in the 1550s. Thanks to English trade with Spanish and Dutch merchants in the Caribbean, the seeds of Indigofera suffruticosa were available in eighteenth-century South Carolina, where it was usually called “Guatemala” or “Bahama” indigo. Because of its hardy nature and beautiful dye, this Latin American species became the principal species of commercial indigo cultivation in South Carolina.

When did indigo cultivation begin in South Carolina?

Indigo seeds (either I. tinctoria or I. suffruticosa) came to South Carolina with the first English settlers in 1670, along with the seeds of a variety of other plants. In the early decades of this colony, European settlers planted a number of different crops as they tried to learn the qualities of the local soils and the seasonal ranges of the climate. The same process of crop experimentation had led the early settlers of Virginia to focus on tobacco. The early English settlers of Barbados, Antigua, and Jamaica had also experimented with indigo as well as tobacco, ginger, sugar cane, and cotton. Once those Caribbean planters perfected their techniques of harvesting sugar and rum from sugar cane in the 1650s, however, they quickly abandoned their experiments and focused on that most profitable plant. Similarly, when South Carolina planters perfected the cultivation of rice in the late 1690s, they temporarily set aside other crops like indigo and focused on the most profitable commodity.

The French Protestant (or Huguenot) immigrants who came to early South Carolina probably arrived with a greater familiarity with indigo than their English neighbors. Because of France’s traditional commercial ties with Spain, and France’s colonies in the Caribbean, it’s likely that some of the Huguenot settlers who established plantations in the Carolina Lowcountry, especially around Santee River delta, in the early 1700s might have been cultivating indigo for their own use.

White Europeans were not the only people living in the Lowcountry of South Carolina, of course, so the story of indigo in this colony involves many other people. To my knowledge, there is no surviving evidence that the indigenous Native Americans of early South Carolina cultivated indigo, so the local Indians could not have introduced it to the early settlers, as they did with maize and tobacco elsewhere.

It is possible, however, that African captives transported to early South Carolina might have had some experience with indigo cultivation in their native land, or had learned about it in the Caribbean before coming here. Enslaved people were certainly deeply involved in the production of indigo in early South Carolina, but it seems unlikely that they would have had the freedom to cultivate the crop and manufacture the blue dye for their own use.

There is very little surviving evidence of the cultivation and production of indigo in the early years of eighteenth-century South Carolina, but it’s certain that some people were growing it here. An early South Carolina planter named Robert Stevens (died 1720), for example, described the process of extracting the blue dye from the plant in the autumn of 1706. The eye-witness observations of “Allegator” Stevens, as he was apparently known, were later reprinted on the front page of the South Carolina Gazette on April 1st, 1745.

How did indigo become a major crop in South Carolina?

The large-scale, commercial exportation of indigo dyestuff from South Carolina to England commenced in 1747, following a revival of interest in the crop. The principal motivation behind this revival was an economic decline caused by a decade of war with Spain and France (the “War of Jenkins’ Ear” and “King George’s War,” 1739–48). Because much of this warfare unfolded on the waters of the Atlantic Ocean and the Caribbean Sea, the complex web of colonial trade networks suffered greatly. South Carolina planters who had focused almost solely on rice, for example, saw their profits fall while insurance rates skyrocketed. At the same time, Britain experienced great difficulty in obtaining exotic goods like indigo, olive oil, silk, and wine through their traditional suppliers, France and Spain. In light of these conditions, the governments of both Britain and her American colonies encouraged immediate diversification.

During the late 1730s and early 1740s, hundreds of South Carolina planters experimented with a variety of plants in the hopes of finding new commodities that were both well-adapted to the local soil and climate and valuable to the British economy. In May of 1744, the South Carolina legislature enacted a stimulus package to “grow” the local agricultural economy. To encourage planters to experiment with the production of wine, olive or sesamum oil (see Episode No. 78), flax, hemp, wheat, barley, cotton, indigo, and ginger, the provincial government offered a cash bounty of one shilling (South Carolina currency) per pound of merchantable produce for export.

The bounty enacted in 1744 was to be in effect for a period of five years, but the fast pace of agricultural experimentation led to an important revision in less than two. Benne seed oil and indigo were the front runners in this competition, but indigo was clearly in the lead. In mid-April 1746, the South Carolina legislature cancelled the bounty on indigo only, stating that so much of the blue dye had been produced recently that the continuation of the bounty was impractical.

The economic drive to produce indigo was further enhanced in the spring of 1748 when the British Parliament enacted their own stimulus package. South Carolina merchant James Crokatt, who had returned to England, successfully lobbied the government to offer a bounty (initially six pence sterling per pound) to the British purchasers of American indigo. That cash incentive, which took effect in 1749, convinced most South Carolina planters to cease experimenting with other crops and to focus on indigo.

But indigo was always a secondary crop. When Britain’s war with France and Spain ended in late 1748, the price of rice quickly improved and continued to be South Carolina’s primary export. Indigo production slowed dramatically after the war, however, and didn’t rebound until Britain again declared war on France in the mid-1750s. From that point onward, South Carolina’s indigo exports increased rather steadily over the next twenty years.

Did Eliza Lucas Pinckney create the indigo industry in colonial South Carolina?

Eliza Lucas (1722–1793), who married Charles Pinckney in 1744, was an important contributor to the success of indigo in South Carolina, but her role in this endeavor has been greatly exaggerated in recent times. As a young lady residing on a plantation on Wappoo Creek, west of the Ashley River, she experimented with the process of growing indigo from seeds and extracting the dye from the mature plants. But she was certainly not the only person undertaking such work at that time, and she certainly had help from a variety of sources.

As demonstrated in a series of newspaper articles published by her husband (under the name Agricola) in 1744 and 1745, Eliza Lucas was following the same experimental steps followed by many of her neighbors. That is, she obtained a supply of indigo seeds from contacts in the Caribbean and read published descriptions of indigo cultivation and dye production. In her surviving letterbook, which contains copies of her outgoing mail, Eliza mentioned that she spent countless hours reading in her father’s extensive library. In Charles Pinckney’s letters to the local newspaper in the 1740s, he shared some of the indigo instructions she had used. The South Carolina Gazette printed extracts from John Parkinson’s Theatrum Botanicum of 1640, Philip Miller’s Gardner’s Calendar (first published in 1731), and the manuscript instructions penned by “Allegator” Stevens in 1706.

David Ramsay’s 1809 book, The History of South Carolina, was the first publication to portray Eliza Lucas Pinckney as a kind of agricultural hero, and later authors repeated and exaggerated the claim. Doctor Ramsay had known Mrs. Pinckney personally and obtained biographical details about her through Eliza’s sons, but he purposefully distorted the story to portray her as an idealized model of American feminine ingenuity. Later authors have amplified and romanticized that ahistorical distortion, especially in recent years.

Descriptions of Eliza Lucas Pinckney as a heroic agricultural pioneer too often ignore the important contributions by her contemporaries, including such local men as Andrew Deveaux, Charles Hill, Thomas Mellichamp, and James de la Chappelle, not to mention the enslaved people of Native American and African descent who performed the bulk of the dirty work for Eliza and others. In short, the idea that Eliza Lucas single-handedly created an indigo industry in South Carolina is comparable to asserting that Elvis Presley single-handedly invented Rock and Roll. Yes, she was a major contributor to its success, but she was not alone in that journey.

Here’s another way to think about this topic. The indigo business in colonial South Carolina included three distinct components: the cultivation of the plant, the production of the dye, and the marketing of the produce. Eliza Lucas Pinckney contributed significantly to the local understanding of the plant’s cultivation, but not to the remaining two components of the business. To tell the whole story of indigo in South Carolina, therefore, you have to include the contributions of lots of other people.

Where was indigo grown in South Carolina?

Indigo was grown on hundreds of plantations in eighteenth-century South Carolina, predominantly, but not exclusively, in the Lowcountry or coastal plain. It was almost always grown in conjunction with other crops, such as rice, provisions (corn, beans, etc.), and cotton. There were a few South Carolina plantations that focused almost exclusively on indigo production, but they were a rare exception that existed for just a brief moment before the American Revolution.

Our colonial-era fields of indigo ranged in size from just a few acres to around eighty acres. Why so small? Because the production of indigo dye also required the construction of expensive vats and other apparatus. In a June 1755 essay published in the Gentleman’s Magazine of London, a South Carolinian named Charles Woodmason stated that indigo planters needed one set of vats for every six or seven planted acres of the crop. Indigo production entailed a significant start-up investment, therefore, which tended to keep plantings relatively small. Two hundred acres of indigo, for example, would require the construction of at least thirty sets of production vats, each of which had to be operated by a team of skilled laborers and kept in constant repair. The expense of such a large endeavor was too great for most planters, so indigo was generally planted in smaller quantities than many other crops in South Carolina.

What’s the process of extracting the dye from the plant?

Indigo’s deep blue dye is obtained by different methods in different cultures. The most common method involves the extraction of natural juices from the leaves through a chemical process of fermentation and oxidation. In early South Carolina, laborers placed freshly-cut indigo leaves and branches into a water-filled vat called a “steeper” to precipitate the natural juices from the leaves. The resulting liquid was allowed to ferment over a number of hours, after which the “liquor,” as it was called, was drained into another vat while the leaves and branches were discarded.

In the second vat, often called the “battery,” laborers agitated the clear liquid with paddles or bottomless buckets to induce a chemical change. As the liquid mixed with air, the molecules oxidized and transformed into a heavier, blue substance. Once the agitation had produced the desired shade of blue, the liquid was allowed to rest and settle. The addition of water infused with caustic lime (derived from burnt oyster shells) further encouraged the heavier blue material to separate or subside from the water.

After several hours of stillness, laborers drained away the remaining liquid to reveal a vat filled with a dark blue mud. Laborers then scooped the mud into cotton or linen bags that were placed in a series of wooden forms and allowed to dry. Before the product was completely hard, workers cut the indigo cakes into small cubes or squares, like brownies, and placed them on racks in a shed to harden. The dried cubes or squares were then packed into wooden barrels, which were then transported (usually by boat) to the port of Charleston and loaded onto cargo ships bound for England.

A number of publications from colonial-era South Carolina describe and even illustrate the process of transforming the indigo plant into a marketable dyestuff. I’ve already mentioned the directions published in the mid-1740s by Charles Pinckney under the name Agricola. In 1755, Charles Woodmason published a two-part essay on South Carolina’s indigo techniques in widely-read Gentleman’s Magazine, which includes an crude illustration of a set of indigo vats. Thomas Mellichamp received a reward from the South Carolina legislature in 1760 for his improvements in indigo production, which were then published in the local newspaper. A 1773 map of St. Stephen’s Parish, South Carolina, contains a valuable illustration that attempts to summarize the entire process of indigo manufacture in a single image. Similarly, a 1780 map of South Carolina includes a great illustration of laborers engaged in two stages of indigo dye production.

Who did the labor of cultivating the crop and processing the indigo dye?

The work of planting, tending, and harvesting indigo plants in eighteenth century South Carolina was done almost entirely by enslaved people of African descent. Besides cultivating the crop, they also built and maintained the vats and other apparatus used in the production process. Likewise, enslaved men, women, and children also shouldered the bulk of the labor involved in extracting the blue dye from the plants and preparing the finished product for exportation.

Some of this work demanded brute force, unskilled labor. Much of it, however, required intellectual skills that could only be acquired through long experience. Determining the duration of the plant’s initial fermentation, for example, played a significant role in determining the finished quality of the dyestuff, as did the duration and character of the agitation of the “liquor” in the battery vat. The delegation of such important roles to enslaved workers denotes a level of trust, and perhaps respect, that helps us to understand of the complexities of slavery in early South Carolina.

In his 1755 description of South Carolina indigo cultivation, Charles Woodmason estimated that fifteen “hands” (that is, fifteen enslaved humans) were required to plant and tend fifty acres of indigo. Once that crop matured, Woodmason advised that it would take twenty-five “very able” hands (that is, experienced, skilled laborers) to transform that fifty acres of plants into indigo dyestuff. He estimated fifty pounds per acre to be an average yield. Thus fifty acres of plants would yield an average of 2,500 pounds of dye, and required the labor of at least twenty-five enslaved workers. Because that means an average of one hundred pounds of product per laborer, the planter had to decide whether the ever-mercurial price of indigo on the British market merited the investment of his time, money, and resources.

When and why did commercial indigo cultivation in South Carolina end?

In the year 1775, South Carolina exported more than one million pounds of dried indigo cakes to England. That record-high output was immediately followed by a near collapse of the industry. The commencement of the American Revolution, which followed years of simmering political tensions, permanently dismantled the traditional mercantile links between American farmers and British customers. Some South Carolina planters continued to grow indigo and to produce the dye during the eight-year war, but they had a difficult time finding customers for the product.

The Continental Congress, of which South Carolina was a member, prohibited the exportation of any goods (except rice, until the summer of 1777) to Britain or any of her allies. South Carolina producers of indigo then tried to market their product to customers in the Northern colonies and to French customers in the Caribbean, but their success was limited. The long-standing bounty on American indigo, created by the British Parliament in 1748, expired in 1777.

At the conclusion of the American Revolution in 1783, some South Carolina planters returned to the cultivation of indigo. Its price on the international market increased for a short while, but European merchants generally found indigo produced by the Spanish and French colonies to be superior to that from Carolina, both in quantity and quality. By the early 1790s, there was a worldwide oversupply of indigo dye, and South Carolina planters realized that chasing after indigo profits like they had before the war was now a futile endeavor.

Meanwhile, mechanical improvements to the cotton gin in the early 1790s transformed that crop into a highly profitable commodity. In response, many South Carolina indigo planters abandoned the blue dye and began growing cotton. By the year 1800, South Carolina was riding a boom of cotton exports while the commercial exportation of indigo had quietly faded into oblivion. European chemists found a laboratory method of synthesizing an indigo-blue dye (aniline) around the middle of the nineteenth century, and the subsequent mass production of the synthetic dye doomed the traditional commercial industry that revolved around organic indigo.

What’s the legacy of indigo in the Lowcountry?

Indigo is a very visible and popular topic of conversation in twenty-first century South Carolina and beyond. A small number of people around the world are advocating for a return to the commercial production of organic indigo dye (and other dyes) from plants grown in a sustainable manner. Scientists working in partnership with farmers are experimenting with the cultivation of indigo plants as a means of amending soil and air quality.

Closer to home, modern efforts to renew local interest in indigo have reintroduced the two imported species of indigo (I. tinctoria and I. suffruticosa) and brought renewed attention to the native species (I. caroliniana). But there’s a significant difference between the historic use of indigo and our modern fascination with the topic. While South Carolinians in the eighteenth century undertook the cultivation of indigo plants and the production of indigo dye in the hopes of making a good profit, most efforts to cultivate indigo in this area today focus on education, explorations of cultural heritage, and expressions of artistic vision.

On the eve of the American Revolution in 1775, there were many hundreds—perhaps thousands—of indigo vats scattered across the South Carolina Lowcountry. Most were built of cedar or cypress wood and have long since disappeared, but a few brick vats still survive. The brick vats built around 1770 at Otranto Plantation in what is now North Charleston, for example, were moved in 1979 to a location on Bushy Park Road in Monck’s Corner, and placed on the National Register of Historic Places in 1989. A few weeks ago, Robert Behre of the Charleston Post and Courier published a fascinating article about a surviving indigo vat on John’s Island.

If you’d like to learn more about this topic, I’ve prepared a short summary of facts about South Carolina indigo history and a list of books and journal articles for further reading. I’ve included a PDF copy of that document at the end of today’s essay. In addition, the Charleston County Public Library periodically hosts indigo-related programs such as lectures, book discussions, and even dye classes, so stay tuned to the library’s website and social media feeds.

Indigo is a beautiful substance that is inexorably linked to a long and painful chapter in the history of South Carolina. By embracing the consoling beauty of indigo and acknowledging the full breadth of its local history, we remember the enslaved people with blue-stained hands whose lives and labors contributed to the success of this community. And we see that indigo truly is part of the fabric of South Carolina history.

For a biographical profile of Robert “Allegator” Stevens, see Walter Edgar and N. Louise Bailey., eds., Biographical Directory of the South Carolina House of Representatives, volume 2 (Columbia: University of South Carolina Press, 1977), 657.

See Act No. 708 in Thomas Cooper, ed., The Statutes at Large of South Carolina, volume 3 (Columbia, S.C.: A. S. Johnston, 1838), 613–16.

See Act No. 737 in Thomas Cooper, Statutes at Large of South Carolina: 3: 670–71.

See the South Carolina Gazette, issues of 8 October 1744, 22 October 1744, 29 October 1744, 1 April 1745, and 23 December 1745.

For more information on the mythology of Eliza Lucas Pinckney, David L. Coon, “Eliza Lucas Pinckney and the Reintroduction of Indigo Culture in South Carolina,” Journal of Southern History 42 (February 1976): 61–76; and Darey R. Fryer, “The Mind of Eliza Pinckney: An Eighteenth-Century Woman’s Construction of Herself,” South Carolina Historical Magazine 99 (July 1998): 25–37.

See “The Indigo Plant Described,” Gentleman’s Magazine 25 (May 1755): 201–3; and “On Manufacturing Indigo Into A Dye,” Gentleman’s Magazine 25 (June 1755): 256–59. Both articles were attributed to “C. W.” (Charles Woodmason).

See South Carolina Gazette, 16–23 August 1760.

See Henry Mouzon Jr., A Map of the Parish of St. Stephen, South Carolina (London, 1773).

William De Brahm, et al., A Map of South Carolina and a part of Georgia (London: William Faden, 1780).

See the graph of “Indigo Exported from South Carolina: 1747–1775,” in John J. Winberry, “Indigo in South Carolina: A Historical Geography,” Southeastern Geographer 19 (November 1979): 91–102.

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