Tag Archives: indigo

New exhibition at the Museo Textil de Oaxaca, May 23 to October 5, 2009: Exhibition Notes

In 1856, an 18 year-old English chemistry student by the name of William Henry Perkin worked away in the laboratory during the Easter holidays trying to find a way to produce quinine from coal. That plant-derived compound was the most effective remedy against malaria at the time, and the bark of the cinchona tree arriving in Europe could barely meet the demand for the medicine. Perkin did not succeed in his effort to convert coal tar into quinine, but instead he stumbled upon a procedure to generate a new substance that stained his flasks a deep purple color. He had discovered by serendipity the first synthetic dye, which he called mauveine. Soon after, other researchers took up his results to achieve an entire family of colorants which revolutionized the chemical industry, saturating our clothes, our homes and our everyday life in vibrant hues along the entire chromatic spectrum.

In this exhibit we would like to display the colors which were familiar to our ancestors. Before Perkin, artists all over the planet obtained remarkable dyes from plants, animals, fungi and minerals. The list of species that were used for that purpose is endless, and the results were brilliant and varied. Many of them were not supplanted by mauveine and the other anilines derived from coal and petroleum because local communities continued to appreciate the quality and beauty of the old dyestuffs. It would be difficult to put together a representative sample of all the natural colorants known around the world; instead, we decided to choose some dyes that have been used in similar fashion by various cultural groups on different continents. First we will show the most significant ones in Oaxaca.

The reds

Cochineal is an insect which feeds exclusively on the prickly pear cactus. It is a relative of the aphids and scale insects that attack fruit trees and garden plants. In the wild, cochineal is a parasite that infests cacti and can kill them. Since antiquity, people living in the highlands of southern Mexico domesticated the host plants for human food, and they also domesticated the insect pest that the cacti nourishes because it produces a blood-red dye. Carminic acid in these insects is a very stable substance which resists heat and sunlight more than other dyes. Water and soap do not modify its color. The compound defends cochineal from predatory insects such as ants, and at the same time it seems to afford them protection against bacterial infections. It is a fast and lustrous dye, but it does not adhere readily to plant fibers such as cotton or sisal. Prior to the Spanish conquest of Mexico, cochineal was used mainly to dye rabbit hair and down, which were woven into cloth. Europeans introduced two animal fibers, wool and silk, which were reddened rapidly by the insect. The Mixtec region was always the center of production, being exported to China to dye satin, to Persia for rugs, and to Europe for cosmetics, oil paintings and sweets. Oaxacan cochineal gave color to the entire world, as attested by antique Turkish weavings in this exhibit. The plague of the prickly pear is so noble that we may eat it with no harm: it was used in former times to distinguish sweet tamales and nicuatole (a Oaxacan jello-like maize dessert) by their pinkness, imitated today with synthetic reds. Distant relatives of cochineal have been used as red dyes in other regions of the world, such as the lac insect, which is a parasite of various trees in southern Asia, and kermes, which infests a species of oak in the countries surrounding the Mediterranean sea.

Before cochineal, the main source of red in the Old World was an herb in the coffee family known as madder, which grows wild in southern Europe and western Asia. A colorant called alizarine, which was synthesized industrially starting in 1868, is extracted from its dried or fermented roots. Madder red, like cochineal carmine, will vary with the mordant (i.e., the compound that helps it bind to the fiber): treated with alum it will yield a dark red, with iron salts a brownish red, and with chromium it will give purple shades. The ancient Egyptians and Persians used this dye; the earliest sample we know of is a fragment of a cotton fabric dyed with madder that was found at Mohenjo Daro in Pakistan, dating from the third millennium before Christ. The plant became one of the most important crops in Europe up to the 16th century, when it was largely replaced by cochineal imported from Mexico. Alizarine remains the preferred colorant for rugs in the Middle East, where its brick red hues harmonize beautifully with other plant dyes and with the natural colors of the wool, as can be seen on a carpet and two pillows woven by Yünçü and Baluch nomads included in this exhibit. A relative of madder provided the most important red dye used in ancient Peru. Another species in the same plant family is used for the same purpose in southeast Asia and Indonesia: khombu is a red dye extracted from the roots of noni, now cultivated in Mexico as a remedy for cancer.

The blues

A single substance, known as indigo, is used to dye a deep blue all over the world; remarkably enough, it is obtained from distinct plants in different areas. In Mexico it is obtained from the Mesoamerican indigo plant, a native species in the bean family, which has been cultivated since antiquity. In India it is extracted from the Asian indigo plant, a close relative of the Mexican species. In Nigeria, in contrast, the source of indigo is a vine that is more distantly related to our plants, though it also belongs to the legume family. In Japan indigo is called ai and comes from a completely different plant, which belongs in the buckwheat family, the Polygonaceae. In Indonesia, a liana in the dogbane family (Apocynaceae) was used for the same purpose. In Europe indigo was formerly extracted from woad, an herb belonging to a fourth botanical family, the Brassicaceae, along with cabbage and mustard. With any of these species, the dyeing process is quite complicated: first, the leaves and tender stems have to be fermented and churned for a long time, and then the colorant is dissolved in lye made with ashes, or in any other alkaline solution. When the plant is fermented, a substance called indican is transformed into indigotine; both are almost colorless. The textile fiber is submerged in the alkaline bath and is then aired out, so that the indigotine is oxidized into indigo, which is insoluble and gives the intense blue color. This is a complex organic molecule which contains nitrogen. A large amount of leaves and stems are required to produce the dye, since the natural concentration of indican is no more than 2 to 4% of the fresh weight of the plant.

Synthetic indigo has been produced commercially since 1897 to dye denim for blue jeans, but craftspeople continue to use natural indigo in various regions of the world. India was the main source of the dyestuff for Asia and Europe since early times, hence the name indigo, which means literally ‘from India.’ The oldest textiles dyed with this colorant come from Egypt, dated 3600 years ago. In Mexico, indigo has been cultivated traditionally in the Isthmus of Tehuantepec, but the most important production took place in El Salvador in Central America, hence the commercial name “añil Salvador,” as it is still known by weavers in Oaxaca. Since it is such a laborious commodity to process, indigo has always been expensive. To reduce the cost, rebozo weavers in this city would mix it together with another plant, called ‘ink leaf’ or muitle, which gives a greyish blue; the disadvantage of muitle is that the color will wash off gradually if it is used alone. We have native indigo and muitle plants growing in pots in the patios of this museum. Oaxacan rebozos, like the better known shawls from Chilapa, Tenancingo and Santa María del Río, were decorated with tie-dye designs in the warp ikat technique. Indigo is the preferred colorant for reserve dyeing throughout the world, as shown by a Yoruba mantle from western Africa in this exhibit.

Purple

In the same way that a blue colorant is obtained from distinct plants in different areas of the world, the ancient phoenicians of the Mediterreanean, the Japanese people and the indigenous cultures of the Pacific coast of Latin America from Jalisco to Peru used a number of species of marine shellfish to dye a beautiful indelible purple. Just like indigo, shellfish purple needs to be exposed to air to be oxidized to become an insoluble fixed colorant, but the process also requires sunlight. The main compound which gives color to the dye has a chemical structure similar to indigo, as its name indicates: dibromoindigo. Even though its formula is known since 1909, it has never been synthesized commercially because of the complexity of the process, which makes it financially unprofitable, the same reason that carminic acid has not been produced industrially. The snails that yield the purple dye use the precursors of the colorant to prey on other marine animals. The amount of dye secreted by an individual mollusc is so minute that it requires great effort and patience to dye a small amount of thread. For that reason, shellfish purple has always been the most highly prized and expensive dyestuff; in Roman times, only the emperor could wear a purple toga. Huge numbers of snails were sacrificed in the Mediterranean and in Japan to extract their colorant in big vats, where entire lengths of cloth would be dyed. Mesoamerican communities, in contrast, have used this resource sustainably, taking the skeins of thread to the seashore, where the shellfish are pried off the rocks so that their secretion drips on the cotton fibers, and afterwards they are placed back carefully on the cracks in the boulders so that they can live on and produce more purple. That is how the warp threads were dyed for the ceremonial skirts of the Zapotec and Mixtec peoples of the Pacific coast of Oaxaca which we show in this exhibit.

The yellows

Unlike the reds, blues and purples, where a few species of plants and animals have been the preferred sources of the dyes in vast regions of the world since early times, the yellows come from a great variety of plants, none of which have stood out commercially like cochineal or indigo. Yellow colorants correspond to two large chemical groups, flavonoids and carotenoids, which are present in numerous botanical families. Flavonoids are very variable compounts which are soluble in water and do not contain nitrogen. The capacity to produce flavonoids was a key adaptation in the evolution of terrestrial plants out of their ancestral aquatic algae because it allowed them to absorb ultraviolet light, thereby avoiding harmful oxidation caused by the sun’s radiation, which is much more intense in the atmosphere than in the water. Some flavonoids have another important biological function: their presence in the flowers attracts pollinizers guided by color, such as insects. Yellow flavones like luteoline provide a glow to the flowers of various species, such as dyer’s broom, a plant in the bean family from Europe and western Asia that is used to dye wool. Since pre-Columbian times, the flowers of xo:chipalli (sulphur cosmos) have lent their color to textiles; they contain a different flavonoid called coreopsin. Central Asian peoples use the flowers called sparak in Uzbek for the same purpose, which also belong in the marigold and cosmos family. In this exhibit we include a woolen fabric from that area decorated with bold warp stripes dyed with a plant flavonoid, madder and indigo.

Carotenoids are present in terrestrial plants and also in algae, fungi and bacteria. Their structure is based on 40 carbon atoms ordered into chains. Their color varies from a pale yellow to orange and red; tomatoes and carrots owe their visual appeal to the carotenoids they contain. These compounds do not dissolve in water, unlike flavonoids. They play a fundamental role in photosynthetic organisms such as plants, where they participate in the process of energy transfer, at the same time that they protect the center of reaction from oxidizing itself. Animals are not able to synthesize them and must ingest them in order to survive, for carotenoids are precursors to vitamin A, which is necessary in various physiological processes. Saffron, a flower in the iris family, yields a carotenoid which lends its color to the Spanish rice dish called paella, and was used by the ancient Greeks as a textile dye. Zacatlaxcalli (dodder) is a parasitic plant without chlorophyll that contains carotenoids and has served as a colorant in Mexico since before the Spanish conquest. Bernardino de Sahagún documented the use of xo:chipalli and zacatlaxcalli by the Aztec people; he also described how yellow and blue dyes were mixed together to achieve green hues. The same procedure was used elsewhere in the world, as there are few natural dyes that will provide a green color directly.

Browns and blacks

Tannins, which are used to tan hides, also serve as dyes that give various shades of brown.
These are complex polymers that dissolve in water. They are produced by many plants as a defense against herbivorous animals. Tannins react chemically with proteins such as collagen in skin to make them bond to each other, allowing them to become more resistant to heat, moisture, and the fungi and bacteria that rot organic matter. Hide is converted into leather this way. The tanneries in Jalatlaco, a section of this city, employed the bark of timbre and other trees for that purpose. The same property that makes proteins bond together in a non-specific fashion serves as a defense for plants because tannins will inactivate digestive enzymes in the gut of herbivores, thereby blocking their nutrition. These compounds are abundant in the bark, the leaves and the fruits of many plants; they have a bitter taste, are astringent (that is, they will dry up the mucous membranes in a person’s mouth) and vary from a golden color to a dark brown. Some of our foods, such as black tea and red wine, contain small amounts of them. The festive attire worn by women in Yalalag is an example of the use of tannins as colorants in Oaxaca: Zapotec weavers use an oak bark to dye the cinnamon stripes that decorate their wraparound skirts.

Iron reacts with tannins to form a black pigment that adheres to textile fibers and is used like ink to write on paper. Lawyers in Mexico are known as huizacheros because they used to prepare a cheap ink with the pods of the huizache (an acacia), which are rich in tannins, mixed with an iron salt. The Mixtec vocabulary of Francisco de Alvarado in 1593 cites the indigenous name of a “black clay for dyeing”. Likewise, the Zapotec dictionary by Juan de Córdova of 1578 translates as “to dye a cloth black” an indigenous gloss that involves the term for ‘clay’ or ‘mud.’ The geographic account of Suchitepec (a Zapotec town in the jurisdiction of Tehuantepec) in 1579 confirms this: “…they dye their mantles and their huipiles… making a yellow dye and a blue one, and a red one and a black one; only the black one do they make out of a black mud…” These quotes from historical Oaxacan documents all refer to the ancient use of iron-rich mud combined with plant tannins to dye black, a procedure which is still followed by Tzotzil weavers in San Juan Chamula in Chiapas, Shipibo cloth painters of the upper Amazon in Peru, and textile artist of Mali in western Africa, as we show in this exhibit through some of their works.

At the end of the show, we hope that our visitors will question the success that Perkin’s discovery has had up till now. In a world ever more aware of environmental distress brought about by our dependence on petroleum and other fossil fuels, we can visualize a new role for natural dyes in our life. Plants and animals can again cover our clothes, our homes and our food with vibrant colors, without contributing to global warming. Cochineal was the main source of wealth for Oaxaca in the past; natural dyestuffs may well generate a new prosperity for the rural communities in our State.

Alejandro de Ávila B.
Curator