plant
Indigo the Plant
Tropical Plant Dye Process Competitor Woad
image of Indigofera tinctoria byKurt Steuber
Indigo: The Tropical Plant
Indigo has been an important source of blue dye for thousands of years. Botanists recognize more than three hundred species of Indigofera growing throughout the tropics. Many species of Indigofera produce a blue dye, but Indigofera tinctoria is the most prized for its capacity to produce an extract that can be concentrated and exported as a commodity. Indigofera yields indigotin, one of the most colorfast natural dyes, compatible with all fibers, including wool, cotton, silk, and linen. Unlike other plant dyes, Indigo dyeing requires neither boiling nor the use of an activating agent (called a ‘mordant’). It is often compared to woad, Isatis tinctoria, an herb of the mustard family that grows in the temperate climates of Europe.
The Indigo plant is a small deciduous shrub that grows from three to five feet in height. The leaves are oval, furrowed on top and dark green below. Only the leaves contain enough indigotin pigment to be worth processing. Freshly cut leaves can be harvested two to seven times a year depending on the climate and growing conditions. Indigofera prefers sandy, alkaline soils that are moist yet well drained. It will not, like woad, tolerate clay. Cultivation of indigo requires labor-intensive commitments to weeding and irrigation. It must be reaped at peak maturity before rains knock it down. Since it starts to ferment immediately after cutting, it must promptly be transported to the processing factory.[1] Consequently, indigo cultivators usually interact directly with dye paste makers.
Indigo Paste.Hiroshima Univ. Dept of Pharmacognosy
Production of Indigo Dye
Having been cultivated throughout the tropics for so long, Indigofera's native origins and its first use as a natural dye are not identifiable. Cultures as dispersed as the Egyptians, the Peruvians, and the Javanese used indigo as a vat dye[2]. However, the first evidence of the industrial production of a transportable pigment paste is thought to have occurred in India.
Indigo dye is chiefly manufactured through a process of fermentation that is unpleasantly odoriferous. (An Egyptian papyrus from 236 BC describes dyers as “stinking of fish.”[3]) The branches are cut, placed in a vat that is then filled with warm water, and mashed. Fermentation begins and continues for more than eight hours until the contents of the vat are remarkably hot and bubbly, and a yellowish-orange pigment appears. The slimy, putrefied liquor is then drawn off to another container and frothed to induce oxidation. This usually involves continued churning of the water for eight to twenty hours. A blue precipitate sinks in flakes, creating sludge at the bottom of the vat. The water is drawn off; the sediment is removed to another vat and immediately boiled to prevent further fermentation. Finally, the sediment is drained, pressed, dried, and cut into cakes for transportation. During the drying process the cut cakes must be frequently turned and kept in the shade, or the quality of the dyestuff degenerates.
These hardened cakes are durable, long lasting, and insoluble in water. In order to make dye baths, lumps of the dyestuff have to be soaked in an alkali solution to render it soluble. In antiquity, the commonly used solution was stale urine. The bath dye water itself is greenish. Fabric or yarn are immersed, and when removed, at first appear yellow. However, contact with air oxidizes the indigo to blue, permanently coating the fibers. Repeated dipping produces successively darker indigo hues. In various cultures, different ingredients are added to the dye vat, ostensibly to influence the tone of color produced. For example, In Morocco, dyers add figs, dates, sugar, and quicklime. In Turkmenistan they add sour wheat flour and sheep bone marrow. In Thailand they add rice whiskey. [3b]
The dye vat, like bread dough or yogurt, can be used almost indefinitely if properly maintained at body temperature and minimally disturbed. However, the liquid in the vat can sometimes suddenly turn dark blue and fail to dye anything. The dye water is potentially toxic, as indigo’s historical use as an abortificient suggests.
Dyers Woad. Image by USDA Forest Service.
Indigo’s Competitor in Temperate Europe: Woad
Woad had been used as a blue dye in Europe since early times. Roman historians remarked upon German and Celtic warriors’ use of blue dye to frighten their opponents. Industrial production of blue dye from woad began as early as the 1230s. By the 14th century, Languedoc and Thuringia were major production centers, exporting mainly to England and northern Italy. The dye paste was even sent as far as Byzantium and Islamic countries where indigo production did not keep up with demand in the textile industry. Great fortunes were made from the woad trade. Most famously, in 1525 a wealthy Toulouse dye merchant was able to guarantee the ransom for Francis I when he was taken as a prisoner in battle by Charles V.[4] Woad growers staunchly resisted the importation and use of the superior indigo dye paste, naming it “the devil’s dye.”[5] Bans against the use of indigo existed in France and Germany from the 14th century until the late 18th century. However, with the arrival of Indigo dye produced in the Americas in the 16th and 17th centuries, wealth from woad production declined. In the 17th century, several royal edicts in France even prohibited the use of indigo dye on penalty of death.[6] However, the Dutch were able to import large quantities of indigo from the East Indies, as they had no woad industry to protect. Because indigo was a cheaper and stronger dye, woad was gradually replaced in European dye shops, despite protectionist policies. In 1737, the use of indigo was legalized in France, causing the decline of centers of woad production, while simultaneously enriching port towns.
Preparing Woad
A Translation from the Stockholm Papyrus, c.300-400 AD, describes preparation of a woad dye bath:
“Put about a talent of woad in a tube, which stands in the sun and contains not less than 15 metretes (sic), and pack it in well. Then pour urine in until the liquid rises over the woad and let it be warmed by the sun, but on the following day get the woad ready in a way so that you (can) tread around in it in the sun until it becomes well moistened. One must do this, however for three days together.” [7]
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NOTES:
[1] Blair B. Kling, The Blue Mutiny; Indigo Disturbances in Bengal 1859-1862 (Philadelphia: University of Pennsylvania Press, 1966) 31
[2] Dauril Alden. “The Growth and Decline of Indigo Production in Colonial Brazil: A Comparative Economic History”. The Journal of Economic History. Vol.25. no.1 (Mar., 1965), 38
[3] Susan Druding, “Dye History from 2600 BC to the 20th Century” http://www.straw.com/sig/dyehist.html
[3b] Anne Varichon, Colors: What they Mean and How to Make Them (New York: Abrams Press, 2006), 186; Nisachon, "Indigo Natural Dye and Handwoven Textiles" (March 2006) www.mekongmart.com
[4] Michel Pastoureau, Blue: The History of a Color (Princeton: Princeton University Press, 2000), 125
[5] Jenny Balfour-Paul, “India’s Trade in Indigo” Textiles from India: Papers presented at a Conference on the Indian Textile Trade, Kolkata, Oct 2003 (Calcutta: Seagull Books, 2005), 364
[6] Ibid., 128
[7] Earle Radcliffe Caley “ The Stockholm Papyrus: An English Translation with Brief Notes.” The Journal of Chemical Education, 4, no. 8 (August 1927), 993 http://www.jce.divched.org/Journal/Issues/1927/Aug/index.html
Created by Kate Long
last update August 2008