Of William Morris: “His obsession with indigo, revealed in letters to his friends, made him the butt of many jokes; as his hands and arms were usually stained blue and he wore classic blue workclothes, his friends nicknamed him ‘Blue Topsy’. It actually took Morris eight years to fully master the indigo discharge process, and he meticulously recorded his recipes in his Merton Abbey dye book.” Balfour-Paul, 1998.
By William Morris: “It would be a week’s talk to tell you all the anxieties and possibilities connected with the indigo subject.” Ibid.
A week’s talk, indeed. This indigo subject is engagingly colorful and surprisingly complex. It begins a long time ago, in worlds far apart. The blue dye, indigo, shows up in textiles from around the world, and despite far-flung origins, the dyes are chemically-identical. The oldest-known samples come from Peru’s Huaca Prieta site, 6,000 year-old materials representing what archaeologists consider the earliest use of cotton fabrics, which are also the most ancient samples of indigo textiles,
Asians and Europeans have long-cultivated a small mustard, Isatis tinctoria, in order to extract a blue dye the English called woad. It must have been an important product; the Greeks had their own word for it – “isatis“, as did Northern Europeans, who called woad “glastum“, referring to the color of the sky.
At some point, a much stronger blue dye appeared in European markets, a substance imported from India which (based on its source) became known to Westerners as indigo. Consequently, the plant, long-used in India, became known as indigo also (in botanical terms, Indigofera, the “fera” ending implying a source, or a provider.)
It was clear the two blue dyes, woad and indigo, gave the same results, and we now understand that both plants produce coloring agents that will eventually yield the compound indigo (also called indigotin), even though the naturally occurring compound in woad is a mixture. In both cases, people process plant material to produce indoxyl which precipitates as indigo, the chemical that makes denim* blue. Indigofera and Isatis are not the only plant sources for this dye; the buckwheat, Persicaria (Polygonum) tinctoria, Oleander relatives Marsdenia tinctoria (ryom), Wrightia tinctoria, & Gymnema tingens, the bean Tephrosia purpurea, Ruellia relative Strobilanthes cusia,** and the daisy Adennostema (Spilanthes) tinctoria have also been utilized historically. Even animals are involved; the regal Tyrian purple, harvested from sea snails, takes its blue hues from indigo.
Generally, indigo dyes are extracted from leaves and stems that are pounded and fermented in water, then dried or precipitated to form a paste or powder. The various dye extracts held great commercial value until synthetic indigo was available at the end of the 19th century. Regardless as to source, indigo dyes are fickle, sharing the unorthodox requirement of “reduction” and “oxidation.” The preparer starts with blue extract (the indican and in woad, some isatan), converts it into a colorless solution (indoxyl, the reduced compound dissolved in water), and then oxidizes the solution (by whipping air into the liquid.) This forms indigo, which precipitates from the solution. For treating fabric in a vat, the paste or powdered indigo is dissolved in a vat (which means it is also reduced to the inoxyl, colorless form) where the fabric will be soaked. When the dyer removes the fabric, its blueness reveals, once out of the vat and in contact with oxygen (thus becoming the final dye, the oxidized indigo). The water-soluble quality of indigo in its non-blue state brings color handily to cotton, a fabric that proves something of a challenge in coloring. But it’s a blind process; great skill and control are required for artisans and manufacturers to realize their dreams.
William Morris knew the challenges of indigo only too well, explaining that getting indigo done is simple, getting it right is not. (Researchers wishing to know more about Morris and his on-going experiments with indigo would visit The Huntington Library to study the Berger Collection, which includes extensive manuscripts, workbooks, and study drawings from the Morris studio.)
The challenges Morris addressed do not seem to have dissuaded him or others; societies and artisans have explored countless strategies and methods to bring blue beauty to material culture. With population growth, globalism, and urbanization, the demand for quantities of raw dye rose to industrial levels, and indigo became one of many plants of imperialism.
In the US, we focus on early Indigo plantations centered around Charleston, SC. That short-lived epoch is one of peoples enslaved, fortunes gained and lost, lands cleared and cultivated. Just prior to the American Revolution, Charleston had managed to surpass a million pounds of indigo per annum, underwriting a third of South Carolina’s export income.
Other countries were more heavily engaged in the trade, with India becoming the primary source for the surging British textile industry. George Watt (1908) tells us “the story of the indigo industry is more entertaining historically and more pathetically instructive than that of almost any other Indian agricultural or industrial substance.” If you read his summary (three asterisks at the end of this post), you’ll see Watt glosses over the 1859 Indigo Rebellion in Bengal, which instigated relocation of indigo cultivation to other areas of India. Watt moved on to summarize, in just a few paragraphs, the history of trade***, ending at a grim realization that: “the researches of the chemical laboratories of Germany threatened the very existence of any natural vegetable dye. They first killed the maddar dye of Europe, then the safflower, the lac and the al dyes of India, and are now advancing rapidly with synthetic indigo, intent on the complete annihilation of the natural dye.”
His prediction came true. Today, though natural indigo remains one of the few dyes with a viable market, that yield constitutes less than 10% of total industrial use; synthetic indigo provides the great bulk of material for textile (and food!) dyes. As with the natural product, the final dye (indigo) must still be reduced to solubility in water for vat dying. Despite the source of indigo, the change, from colorless to blue when the fabric is exposed to the atmosphere remains magical.
To round things out, indigo can also be used to manufacture pigments. Mayans combined extracts (from the native Indigofera suffruticosa) with clays to produce Maya blue for wall paintings. Murals in Mexico’s Colonial churches, notably those by the indigenous artist Juan Gerson of Tecamachalco, utilized Maya blue into the 16th century.
It’s a large, multi-cultural, multi-lingual story. If you take the time to read the Watt summary, you’ll see that Charles II, once restored to the monarchy, brought dyers from Belgium to resurrect the indigo industry. Perhaps the notoriety radiating from indigo at the end of the 17th century was a reason Isaac Newton decided to tuck a bit of indigo into his rainbow. Like Pluto, there’s on-going pressure to throw this color out, as an extravagance. But I cling to indigo as the rich hue between violet and blue.
Postscript: The pursuit of indigo synthesis led to significant gains in understanding of organic chemistry, but nothing is easy. The compound formed by Indigofera is indican (an indole with attached sugar, C14H17NO6) The compound isatan is derived from woad, with the formula C16H12N2O3. The analytical breakdown product from woad, isatin, was first isolated in 1840 by Otto Linné Erdman and Auguste Laurent, through oxidation of indigo dye using nitric acid and chromic acids. The related indole was discovered later, by Adolf Baeyer, as he was working on studies in synthesizing indigo, which were finally realized in 1878. Degrading indigo with oleum (fuming sulfur dioxide), Baeyer generated indoxyl, as well as oxindole, eventually generating an oxygen-free compound we call indole (C8H7N) today. This suite of compounds is related to the essential amino acid tryptophan, and through various reactions to a host of powerful psychoactive (LSD), poisonous (strichnine), cancer-treating (vincristine), and hormonal (auxin) organics.
*Denim is a coarse, dyed cotton fabric, a kind of serge, originating from the southern France town of Nîmes. Its source data, serge de Nîmes, was contracted to the word denim.
** The Landian Yao peoples of Yunnan, China specialize in blue dyes, extracting indigo from Strobilanthes and other plants. See: Shan Li, A. B. Cunningham, R. Fan and Y. Wang, 2019. “Identity Blues: the ethnobotany of the indigo dyeing by Landian Yao (lu Mien) in Yunnan”, Southwest China, J. Ethnobiol Ethnomed. published on line 19 Feb 2019. Follow the link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6379986/
*** Watt’s summary from The Commercial Products of India, Being an Abridgement of “The Dictionary of the Economic Products of India. 1908 (free on Google Books): “The main facts may, therefore, be here briefly recapitulated : — There is abundant evidence in support of the belief that when Europeans first began to purchase and export the dye from India, it was procured from the Western presidency and shipped for the most part from Surat. It was carried by the Portuguese to Lisbon and sold by them to the dyers of Holland. It was the desire to secure a more certain supply of dye-stuff that led to the formation, in 1631, of the Dutch East India Company, and shortly after to the overthrow of the Portuguese supremacy in the East. The success of the Dutch merchants aroused the jealousy of Europe. The woad growers and merchants of Germany, France and England were threatened with ruin, and to protect them nearly every Woad. country passed edicts rendering the importation or use of indigo a criminal offence punishable by death.
In 1608 England learned the art of indigo-dyeing, and in the reign of Queen Elizabeth its use was permitted along with woad. Curiously enough this mixing of woad with indigo survives to the present day, and to meet this demand a small amount of the woad is grown here and there over Europe, and even in England. The opposition to indigo was, however, so strong that it was again, on the pretext of being poisonous, prohibited, and in 1660 Charles II. had to procure dyers from Belgium to once more teach the English the art of using the dye. As already shown, the effect of the persistent export of the dye from India, conducted by the East India Company, had the effect of stimulating the Spanish, French, Portuguese and English colonists to make strenuous efforts to produce the dye in many countries outside India. And so successful were they that for a time they ruined the ancient Indian traffic. But Macpherson (Hist. Europ. Comm. Ind., 1812, 200) speaks of the East India Company having voluntarily given up the importation of indigo into England “in order to avoid a competition with the British Colonists in the West Indies and the southern provinces of North America. About the year 1747 most of the planters in the West Indies, particularly in Jamaica, gave up the cultivation of indigo in consequence of the high duty imposed upon it ” ; ” the planters of Carolina and Georgia were never able to bring their indigo to a quality equal to that of Guatemala or St. Domingo.” But political difficulties occurred with America and France, and at the same time sugar and coffee had proved even more profitable in the West Indies than indigo. The impetus was thus given for a re-establishment of the Indian traffic, and, as one of the many surprises of the industry, the province of Bengal was selected for this revival. It had no sooner been organised, however, than troubles next arose in Bengal itself through misunderstandings between the planters, their cultivators, and the Government, which may be said to have culminated in Lord Macaulay’s famous Memorandum of 1837. This led to another migration of the industry from Lower and Eastern Bengal to Tirhut and the United Provinces. Here the troubles of the industry did not end, for, just as indigo had ruined ” the Weid Herrn,” (this references wealthy textile merchants in Germany, the “gentlemen of woad”) so the researches of the chemical laboratories of Germany threatened the very existence of any natural vegetable dye. They first killed the maddar dye of Europe, then the safflower, the lac and the al dyes of India, and are now advancing rapidly with synthetic indigo, intent on the complete annihilation of the natural dye. Opinions differ on many aspects of the present vicissitude; meantime the exports from India have seriously declined, and salvation admittedly lies in the path of cheaper production both in cultivation and manufacture. These issues are being vigorously faced and some progress has been accomplished, but the future of the industry can scarcely help being described as of great uncertainty. The issue is not the advantage of new regulations of land tenure, but one exclusively of natural versus synthetic indigo. (The Botanical Library holds a copy of Watt’s Dictionary)
Novel Indole Derivatives as CNS acting agents – Dr Swathi Konda, 2015 BookRix (Google Books)
Tree of Life – Acanthaceae. http://tolweb.org/Acanthaceae/20878