Chemical Groups of Colours
We can divide botanical dyes into phytochemical groups. The major groups are: Anthraquinoids for reds, Flavonoids for yellows, Indigoids for blues, tannins for browns; most dye plants contain elements from several groups and the balance of these can vary according to the time at which the plant is harvested. Thus natural colours never appear flat but change according to the light and always appear rich through their combination of molecules catching our eye, creating a complex optical mixture.
Anthraquinoids
Most red dyes are anthraquinoids, a combination of 2 chemical structures: anthracen, a carbon structure made of 3 connected rings and quinon which is made of oxygen bound to carbon. The dyes in this family are some of most colourfast that exist. We find them present in the immense botanical family of the rubiaceae. The most famous in this group is madder, rubia tinctorum or “manjeet” in India, rubia cordifolia.
Alizarin is the most iconic anthraquinoid, present in madder roots which are rich in the highly coloured glycosidic compound ruberythric acid.
Purpurin
Other anthraquinoid molecules present in madder are lucidin, purpurin and purpuroxanthine. Morindone is another commonly found red colourant found in the Morinda plant, mainly in the roots.
Reds are the oldest of tones used by man: a red-hued clay, used by our Stone Age ancestors for bodily anointment was ground and painted with over 50 000 years ago[1], using iron oxide, Earth’s most common pigment. Cottons from India’s Mohenjo-daro site were dyed with madder, where the long roots are crushed for pigment, a technique dating back to the third century BC. Indeed we grew madder and other rubiacea such as rubia sikkimensis, rubia argyi, morinda and gallium tinctorium, to crush the roots and aim to find the most intense red we could. We fantasised about Turkey red, regulating the recipes and reproduction of this intense scarlet.
Reds represent sensuality and ardour, rapacious power and also valour; many artists were entranced by the power of red, from vermilion to carmine, notably Rothko and Van Gogh who wrote to his brother Theo: “I sought to express with red and green the terrible human passions…Everywhere is a battle and antithesis of the most different reds and greens” he said of his painting The Night Café, in 1888.
[1] An atlas of rare and familiar colour, the Harvard art museum.
Flavonoids
Flavonoids are responsible for many of the bright vivid colours in plants and represent the source of all the beautiful golds , rusts and yellows. Indeed flavus in latin is the word for yellow.
Most flavonols however absorb light waves measuring between 325 and 370 nm thus making them very faint to the eye. The use of metallic mordants is thus necessary to intensify the colour to the human eye and bond the molecules to the fibre.
Quercetin
There are a multitude of flavonoids in nature, over 7000, the most commonly used for textile dyeing are: Luteolin which is found in weld, dyers camomile Anthemis tinctoria and Cytius scoparius, and Apigenin (often used as a medicine to reduce stress and relieve muscle tension), found in many chamomiles and commonly used in Turkey where Anthemis chia is used to dye the yellow wool for carpets.
Other well known flavonols are galangine, quercetin and kaempferol, present in many tinctorial plants such as fustet, osage and Indian marigold (tagetes), this flavonol is a known anti-inflammatory and helps with people receiving treatment for cancer. Indeed many flavonols are known for their beneficiary bio-active effects.
Yellow is intensely used in painting, often for representing contraries: from energy and sunshine to wanton frivolity and Asian wisdom, yellow has been employed in art since long before Lascaux. However often linked to heavy metals such as those in lead tin paint, crocoite, from Siberia and chromium, the new element identified by Louis Nicolas Vauquelin in 1797.
In the natural world, Yellow predominates and can be reproduced by a variety of plants from weld to marigold, to see the entrancing yellows in our colour palette, look
Carotenoids
A wonderful yellow/orange colourant, present in so many plants we estimate over 3.5 tons of carotenoids are produced in Nature every second. [1]Their name comes from carotene, isolated from carrot roots in 1881.
Wassily Kandinsky said “Orange is red brought nearer to humanity by yellow”, orange is known to be the colour of divine illumination, transformation and flamboyance, from the colour of a monk’s robe to that of a sweet winter tangerine.
The most renowned orange, cultivated throughout the Mediterranean, Persia and Southwest Asia, comes from Crocus sativus; saffron. In Iraq, 50 000 year old cave artworks were unearthed containing beasts painted with saffron pigment.
Turmeric, often used throughout the Indian subcontinent is equally renowned as a botanical pigment but when using it on fabric we must be careful as it has little lightfastness and fades when exposed to sunlight.
Painters who famously used orange the most are those who painted the most outdoors: the impressionists. Eager to replicate the entrancing tones of nature glowing under a warm sun, painters such as Cezanne, Pissarro, Monet and later the famous post-impressionist Gauguin used orange to translate the impact of radiant sunlight. His work in Tahiti from Pastorales tahitiennes to Mata mua, he constantly uses orange imbued figures or orange infused landscape, to translate the warm exotism of the Tahitian islands through the resplendent radiance of this colour.
[1] Le monde des teintures naturelles/ Dominique Cardon
Paul Gauguin
Indigoids
Probably the most famous natural colour is indigo, the colour of myths.
“The colour blue is that of nature’s leviathans-becalming and subsuming in equal measure” Narayan Khandekar. Famously, the master artist of blue, Yves Klein describes:“the real blue was inside, the blue of the profundity of space, the blue of my kingdom, or our kingdom. The immaterialisation of blue, the coloured space that cannot be seen but which we impregnate ourselves with.”
Derived from a wide number of plants, ancient civilisations did not realise the pastel blue they were using to go to battle in, was the same chemical element as the deeper mysterious blue they had heard about, originating from Asia and Persia; this element is indikon, or indicum, literally, the blue of India.
Bronze age inhabitants of the Indus Valley cultivated Indigofera tinctoria from between 3300 BC and 1300BC[1]. Exported to Ancient Greece and then to Rome from India, rare indigo was used as both a cosmetic ingredient and a cloth dye from the 2nd millennium BC onwards. When indigo plantations became multiple with the spread of the colonies in the 17th century , Indigofera tinctoria supplanted woad as the world’s main source of blue.
Indikon
Indican, the glucoside, C14 H17 NO6, that occurs in plants yielding indigo and from which indigo is obtained, needs to be decomposed by enzymatic hydrolysis to form indoxyl molecules that will turn into indigotin through exposure to oxygen or indirubin, the more purple tone of intense blue.
Since the Egyptians, we have known to make indigo vats transforming the plants available in each continent, from Indigofera tinctoria to Indigofera suffruticosa, Strobilanthes cusia to Persicaria tinctoria and the famous Isatis tinctoria of woad, man has developed a way to extract indigo from local plants to make a range of blues.
Woad was cultivated vastly throughout Europe and is known more famously as “pastel” in France where blue vats were developed in the middle ages, enabling medieval dyers to render many shades of blue and green. France was Europe’s greatest producer of woad throughout Picardy and Languedoc, creating fortunes along the way, so much so that one Castillian woad merchant, Jean de Bernuy could stand as the main guarantor for the ransom of King Francois the 1rst after his capture by Charles V of Spain. Woad expanded as a popular crop in England so much so that grain production became threatened as woad was six times more profitable. It is notable as Britain, the first country to embrace imported indigo was also the last to abandon woad.[1]
Woad is equally used in traditional Chinese medicine as a plant that can “cool the blood” as it is known to be an anti-inflammatory that can cool fevers and cure dizziness, often used to cure flu.
Many recipes exist throughout the globe to reduce indigo through fermentation, we will address these in a separate chapter.
Many of our members are specialists in indigo dyeing, notably indigo dye master David Santandreuand Archaeologist Ana Roquero who has equally studied the traditional methods of pre-Columbian populations and identified several traditional Mayan recipes.
Probably the most entrancing of indigos are the deepest blues, found in traditional African cloths, in China where they are beetled to reveal the iridescent sheen of scarabs, in Burma where indigo is combined with tannins and Japan where sukumo fermentation has been studied extensively. We know there that the bacteria responsible for indigo reduction is Bacillus alkaliphilus, in Korea it was identified as Alkalibacterium. A famous study is that of the modest G. Van Laer from Verviers in Belgium named “Aide memoire pratique du teinturier” which describes the many vats charted and compares the deep blues obtained.
Today, indigo is probably identified mostly with denim and the production of blue jeans.
This implies the usage of synthetic indigo in most cases and a reduction of the vat using a mixture of caustic soda and sodium hydrosulfate. Indeed, since the German chemist Adolf von Baeyer identified the chemical structure of indican in 1865, he took up the challenge to synthesize it with the support of BASF who then launched the first synthetic indigo in 1897 marketed as “Indigo Pure”. [1]It took about thirty years for synthetic indigo to take over the market but now 98% of denim is still dyed with synthetic, benzene derived indigo. The resulting bath from synthetic vats is extremel y toxic and the waste-water incurred most damaging for the environment both for aquatic life and the soil contaminated by these waters. Populations living nearby sites of denim production are always highly affected by the damaging combination of sulfates and sodium dithionite, making the annual production of jeans an environmental problem we must all seek to resolve.
Lojitech, a denim producer in Morocco is one of the first to offer natural indigo dyeing as an industrial option, made with locally grown indigo. In the US, Fibreshed have made fantastic efforts to create more natural indigo options, both cultivating and dyeing indigo locally.
