By Katherine Schlosser
I remember the first dress that made me feel good about myself. I was 17 and looking for something to wear to a dance, not formal, not cocktail, but a Sunday dress, as we called them so many years ago. It was a slim dress (I could get away with that in those days), with three-quarter length sleeves, a prim boat neckline, and a wide shiny ribbon sash at the waist. The dress was indigo blue. I remember nothing about the boy or the dance, but I still remember the dress.
Indigofera tinctoria, indigo, a member of the Fabaceae family, has that effect on people. The dye it produces is exotic, soothing, luxurious. A color of devotion, wisdom, and justice. For all its attributes, it has also been the cause of much labor for planters, free men of color, and slaves over the years, requiring large numbers of laborers to grow and harvest enough leaves to produce the dye.
The oldest record I know of is a small piece of 6000-year-old cotton cloth on which the indigo dye is still detectable. This was discovered in a preceramic site of Huaca Prieta on the north coast of Peru during an archeological dig. Other snippets of dyed cloth, wool, and silk from archeological digs were dated 1,500 years later than those in Peru. Those others were found in archeological sites from India and Africa, to Italy, Greece and in Europe, as well as in South America.
There are other plants that produce a blue dye, especially Isatis tinctoria, woad, a primary competitor with indigo. But none have quite the same opulent quality as indigo, or the stability.
Indigo grows around the globe in tropical to subtropical areas. In the United States, we have eight native indigo species, most centered in the southeast. Several will produce indigo dye but not always of top quality. Indigofera suffruticosa, also known as añil, produces a rich, stable color close to I. tinctoria, as does I. guatemalensis, or Guatemalan indigo. I. caroliniana makes a nice dye, but paler. Indigofera tinctoria, true indigo, is the best, and seeds of the plants were brought to this country in the 1700s and grown in Louisiana, Florida, Georgia, the Carolinas, Virginia, and Tennessee to produce dye for commercial use.
Indigofera tinctoria can grow from 3 to 5 feet tall with light green pinnate leaves (with 4 – 7 pairs of leaflets) and sweet pink or violet flowers that bloom in July or August. In its native tropical Africa, south central Asia, Mexico, and South America, it can be either perennial or annual, or even evergreen in warmer locations. It grows best in full sun, with a little shade from the hottest part of the day, and needs regular rainfall. It also has been used in the past for a variety of medical ailments, and against insect and serpent stings or bites.
It requires 30 tons of indigo leaves (one acre) to produce about 26 pounds of pigment. Leaves are harvested, separated from stems, dried, and processed to produce the pigment. That happens after the land has been prepared, seeds planted, weeding on a daily basis (plants don’t do well when crowded), and harvested twice a year. The labor required is intense, and in the 1700s and 1800s, was usually managed by slave labor and/or free men of color.
Those who worked in the fields were subject to more than just hard work in the hot sun. Many had to endure the “putrid effluvia of the coastal swamps,” as well as stagnant pond water and mosquitoes. Disease and death was not uncommon in southern fields.
Eventually, so many planters around the world were growing and exporting indigo that the market began to collapse. More than a million pounds of dye had been exported from the U.S. in 1775. In the southern U.S., cotton gained notice, along with rice, as indigo was removed and replaced. Indigo plants deplete the soil of nutrients rather quickly, so frequent labor-intense alternating of crops was necessary as well. Some planters still grew indigo but on a smaller scale.
True indigo is still grown commercially. There are artists who grow their own plants and process them to make the pigment they need for the renowned deep blue. A 5mL (.17 oz) tube of watercolor sells for $10, and a 37 mL (1.25 ounce) of oil paint sells for about $18. When you buy artwork, you are not only paying for creativity, but for materials as well!
Synthetic indigo is common now with the advantage of lower cost. As is often the case, lower cost doesn’t always mean equal products, and in this case, synthetic indigo carries the costs of diminished depth of color and damage to the environment. Unlike natural indigo, synthetic indigo is dependent on petrochemicals for processing, which are toxic and require appropriate disposal, adding to the expense. Water remaining from natural indigo processing is free of chemicals and can safely be returned to the earth.
Indigo appears in clothing, on pottery and ceramics, and on artists’ palettes. It is also in every rainbow most of us see, though not everyone can see it. In the spectrum of colors—red, orange, yellow, green, blue, indigo, violet—for some, distinguishing between blue and violet is difficult. Spotting the indigo is considered a sign of hope, joy, or for some, luck. With the next rainbow you see, search for the indigo and give a little thought to the human costs that brought that beautiful color to our palettes.
And think about that pretty indigo-blue dress on a shy teenage girl who sees indigo in rainbows.
Indigo species in the U.S. and the states in which they are native:
Indigofera caroliniana Mill., Carolina indigo – NC, SC, GA, FL, AL, MS, LA
Indigofera colutea (Burm. f.) Merr., rusty indigo – FL
*Indigofera decora Lindl., Chinese indigo – GA
Indigofera guatemalensis Moc. & Sessé ex Prain & Backer, Guatemalan indigo – PR, VI
*Indigofera hendecaphylla Jacq., trailing indigo – FL
*Indigofera hirsuta L., hairy indigo – SC, GA, AL, FL
*Indigofera kirilowii Maxim. Ex Palib., Kirilow’s indigo – TN
*Indigofera lindheimeriana Scheele, Lindheimer’s indigo – TX
Indigofera miniate Ortega, coastal indigo – TX, OK, KS, AL, GA, FL
Indigofera oxycarpa Desv., Asian indigo – FL (threatened)
*Indigofera parviflora K. Heyne ex Wight & Arn., nom. Inq. – AL
Indigofera pilosa Poir., soft hairy indigo – FL
Indigofera sphaerocarpa A. Gray, Sonoran indigo – NM, AZ
Indigofera suffruticosa Mill., Anil de pasto – TX, LA, GA, SC, NC, FL, PR, VI
*Indigofera tinctoria L., true indigo – NC, SC, MI, TN, PR, VI, NAV
*= non native species growing in the U.S.
¹ History of Indigo & Indigo Dyeing. Indigo History, WildColors, http://www.wildcolours.co.uk/html/indigo_history.html. Accessed 7-08-2022.
² Winberry, John J. 1979. Indigo in South Carolina: A historical geography. Southeastern Geographer. Vol. 19, No. 2, p.91-102. Available online: https://www.jstor.org/stable/44370692?seq=1&cid=pdf-reference#references_tab_contents. Accessed 08-07-2022.
Photo Credits: 1) Indigofera suffruticosa (Kohler’s Medicinal Plants, 1887, Public domain); 2) Woad-dyed fabric (Local Color Dyes, http://www.localcolordyes.com); 3 & 4) Añil-dyed fabric (Norma Schafer: Oaxaca Cultural Navigator); 5) Indigofera tinctoria (Kurt Stuber, Creative Commons); 6) Indigo-dyed fabric (Affordable-kind-craft.com.au).
Medicinal Disclaimer: It is the policy of The Herb Society of America, Inc. not to advise or recommend herbs for medicinal or health use. This information is intended for educational purposes only and should not be considered as a recommendation or an endorsement of any particular medical or health treatment. Please consult a health care provider before pursuing any herbal treatments.
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Katherine Schlosser (Kathy) has been a member of the North Carolina Unit of The Herb Society of America since 1991, serving in many capacities at the local and national level, including as a member of the Native Herb Conservation Committee, The Herb Society of America. She was awarded the Gertrude B. Foster Award for Excellence in Herbal Literature and the Helen de Conway Little Medal of Honor. She is an author, lecturer, and native herb conservation enthusiast eager to engage others in the study and protection of our native herbs.