Disclaimer: after the report on techwear, Milone is writing again in our columns. And what could be more normal for this denim enthusiast than to tell you about the pigment that is inseparable from them: indigo.
Blue... royal color. Color that inspires fear, as with the Tuaregs (“the blue men”). Color of workers, long despised during the Middle Ages, or on the contrary venerated by the pharaonic Egyptians who saw it as a lucky color. In Hinduism, it represents the deity Krishna.
Note: in Sanskrit, “Krishna” also means “blue-black”.
But above all, it has long been difficult to master because its manufacture is so complicated : blue pigments were very rare, and the most beautiful shades, the deepest, like “ultramarine blue” were expensive.
Indigo is a purplish-blue (sometimes reddish) dye extracted from different plants . There are around a hundred indigo shrubs and plants, of which only around ten can be used for dyeing. Indigo dyes are found almost everywhere in the world, knowing that Oriental and American plants are generally much richer in coloring principles (indican) than European plants.
Planting indigo shrubs in the United States.
I will only talk about the main plants and techniques, which are really numerous, and which interest us. Indeed, indigo was not only used as a dye for cotton, wool, etc., but also for hair or wood... as well as as a medicinal plant.
Speaking of which, we still treat certain illnesses, like clothing addiction, through massive purchases of indigo denim.
The main plants with indigo pigments
Dyers’ pastel
It is a plant commonly known under the names Herbe de Saint-Philippe, Varède, Guède or Herbe du Lauragais. It was used as a medicinal and dyeing plant (relating to dyeing, editor's note) by the Greeks and Romans during Antiquity.
Dyers' pastel flower. Yes, it is yellow!
The Breton, Celtic and German “barbarians” painted their bodies with it during religious rituals, as well as before fighting in order to frighten the enemy, causing a certain fear in the Roman legions.
Then, it was widely cultivated during the second half of the Middle Ages and the Renaissance in Europe (mainly in the south of France and Thuringia in Germany) for the production of a blue dye, extracted from leaves . It will be dethroned by indigo, then by synthetic dyes, but we will come back to that later.
It is from these leaves that the pigment is extracted.
Almost all Mediterranean countries used dye from dyers' pastel, as did the British, Dutch, Portuguese, etc. It was preferred to indigo pigments which were still rare at that time - and therefore very expensive - since they were imported from India.
A particularly curious use of coloring principles from pastel was made by the Chinese in the 19th century: the coloring of green teas, called "iced", for the exclusive use of European "barbarians". This made the fortune of certain traders.
It is also a blue powder used as a pigment for paints. Incorporated with calcium carbonate, it makes it possible to obtain sticks used for drawing (the famous “pastels” from our plastic arts classes).
The entire pigment extraction process takes place over a period of approximately two years. This was mainly done around the south-east of Toulouse: Lauragais or “Land of Plenty” (you will understand why later).
Harvest :
The harvest is done on plants approximately 4 months old. When mature, the leaves begin to turn yellow, and are removed quite easily by tearing or cutting. Mowing is carried out from mid-June until the end of September, in various regular samples (maximum 4 or 5 passes).
The cocagnes:
After washing to remove dirt, the leaves are taken to the “pastel mill”. The latter is composed of a large grindstone with a horizontal axis, rotating in a stone trough where the leaves to be crushed are placed. They are crushed there to extract a pulp.
The photo is a bit blurry, but we can see very clearly what the beast looks like.
This pastel paste is then left to dry in a shed, for a time varying depending on the location, the weather and the preference of the producer. Once it reaches the expected drying time, it is crushed and rolled by hand into a fist-sized ball. These are the “cockles” or “cocagnes” (you understand now if you have followed carefully).
They are then placed on racks (a bit like refining cheeses) so that they finish drying. The weather here too is variable, from one to two months. Once hardened and dehydrated, the shells, now called “Cocagne pastels”, can be marketed to be used in the preparation of the dye material: “agranat”.
A pastel de Cocagne, or the hybrid between stone and truffle.
The agranate:
“Agranat” is a pastel paste made at the beginning of the year from crushed cocagnes, reduced to powder in a mill, and sprinkled with water or urine to cause fermentation. This paste requires frequent stirring to control its temperature and ensure that the process is permanent.
Once dry, the pastel paste provides a dye powder which can be put in a barrel or bag, to be transported or stored (up to 10 years in optimal conditions).
For the record, the vile odor emitted during manufacturing forced the craftsmen to work in the countryside, far from the cities.
Vat dyeing for pastel:
The coloring pigment (or indigotine) of agranate cannot be used directly because it is insoluble . It is then necessary to use a so-called “vat” process to transform the indigo into a soluble molecule. There are various processes, each artisan had his own jealously guarded recipe.
We thus obtain “leuco-indigo” with a greenish-yellow color. It can impregnate textiles (cotton, wool, etc.) by immersing it in the bath, for a longer or shorter time depending on the density of the desired color. Then when it is taken out, an oxidation phenomenon appears, giving a more or less intense blue color.
This culture declined - almost disappearing - with the arrival of indigo from India in the 17th century, and chemical dyes in the 19th century.
Thanks to a renewed interest in ancestral techniques, certain artisans are bringing the woad up to date. Both for dyeing and for the non-industrial production of pastel sticks for drawing, or even for interior decoration with organic paints with natural pigments.
For the record, just to shine in society, know that Bayeux violet and Argentinian gray contain pastel.
Indigo and cultivation of the indigo tree
Also called dyer's indigo, or Indian indigo. It is the most widely used natural and vegetable indigo, and the one which supplanted dyers' pastel: its colors were deeper and more intense, and the pigments approximately 20 times more active.
There are traces of its cultivation in India 4,000 years ago, and of its use in the Middle East and Ancient Egypt for almost as long.
There are multiple indigo bushes around the world, and each country and region had its own way of producing indigo. But the main one, used with Indigofera Tinctoria which is mainly grown in the warm regions of Asia, America and Africa, is quite simple.
Indigofera Tinctoria flower.
They began by placing the shrubs in vats of pure water to macerate them, generally for 24 to 48 hours. This was followed by a fermentation stage, where the bath was stirred so as to introduce as much oxygen as possible so that the indigo settled at the bottom.
They filtered this liquid, boiled it to reduce it so that the liquid evaporated, and recovered the dry material which is indigo. They ended up pressing him together.
Dyeing process with indigo
There are different indigo dyes from the indigo tree, but the most used today dates from the 18th century. Found by European dyers, it is close to that used for pastel. In fact, this is also a so-called “vat” process. This name comes from the fact that wooden or enamel vats were once used, and not metal cauldrons.
The process consists of making indigo soluble in a liquid (pure water) which is an anaerobic medium (therefore without air) and basic. For this, reducing chemicals (to make it soluble) and alkali are used.
Originally it was mainly lime and iron sulfate. But nowadays, the preferred use is that of sodium hydrosulfite or sodium dithionite as a reducing agent; and ammonia or soda or sodium carbonate as alkali.
Representation of work in an indigo factory (note: we specify in passing that at the time, the use of the term “negro” was not yet pejorative).
Depending on the artisans and their method, we use a cold or temperate recipe (around 50°). The resulting color is yellowish, but exposure to air causes oxidation, allowing the long-awaited hue to turn blue. Like with pastel.
Results with Indigofera Tinctoria give a dark, purplish blue, even reddish, but the shades may vary depending on the other plant varieties used.
Almost all of the dye is then fixed, the excess being removed by washing, or sometimes even by “rubbing” techniques (ah, “used” jeans...). You should know that it holds exceptionally well on wool, but not so well on linen and cotton , to the delight of denim addicts (here the pretty denim washes).
Wool fibers dyed with Indigofera Tinctoria.
There is another dye made from the indigo tree, known as Saxon blue or indigo carmine. The latter is blue-green in color, and was found in the 18th century by working indigo with sulfuric acid. It is also a color that is starting to be popular again.
As I told you previously, there are different varieties of shrubs . The Indigofera Tinctoria is the most used because it is also the plant that has been most established in the world, thanks to its ease of acclimatization. But we find certain species that have been and are still used for different types of dyes, mainly traditional:
- The frank or "bastard" indigo tree, Indigofera Anil , grown in the West Indies and other parts of America. Its culture was particularly exploited in the 17th and 18th centuries.
- Persicaria Tinctoria - or Dyer's Knotweed - native to China. Cultivated and exploited for millennia, both for its dyeing and medicinal properties, it was subsequently imported to Japan, Korea and also Europe, where it undermined pastel thanks to its dye rate 3 to 5 times higher. .
- Philenoptera Cyanescens, liana-indigo, "gara" in French-speaking Africa and "Yoruba indigo" in English-speaking Africa. Cultivated mainly in West African countries for a very long time (still today), it is mainly used for artisanal and traditional products (batiks, etc.). It is starting to be exported for more high-end use because its shades are currently appreciated.
Dyers' knotweed: it was its arrival in Europe that largely contributed to the decline of pastel.
All these dyes are used with more or less identical techniques : cultivation or picking of the plant, extraction of the pigment, assembly of the vat, dyed thread (or canvas) which emerges from the dye bath, and then weaving.
But one remarkable thing, because very little or no exchange took place between countries and cultures, is that everyone found a way to obtain this blue.
Whether in China, Egypt or Mali, how did dyers, weavers, or simply curious people, get the idea that behind a few leaves could be found a pigment giving a color that would become so popular? And above all, how did they have the idea and the genius to manage to fix it on a fabric without having any interaction between them?
Excerpt from the beautiful book "Indigo, The Color That Changed The World" by Catherine Legrand, which takes a world tour of the use of pigment.
But there are other, lesser-known types of blue dyes that are just as interesting. I'm not going to dwell on them, but just present them to you, because they are more or less linked to indigo (not chemically, but at least historically). They have not been widely used as clothing dyes because they are either too expensive or not very interesting.
- Lichen, some species of which contain a purple pigment, called orrel, used since very ancient times for dyeing fabrics and wool.
- Ultramarine, a true compound of blue lazurite (blue constituents of lapis lazuli ) and iron pyrite. It is one of the most difficult to manufacture and rarest blue pigments, therefore very expensive. It gives an extremely varied palette of blues, and has always been considered the “Rolls” of blue pigments. Kings and emperors always loved it, it was a pigment which allowed one to show one's position in society.
- Azurite or azure from Germany: be careful, fake ! It was often sold as real ultramarine, when in fact it was just azurite minerals ground into powder and mixed with various binders. It was widely used in painting.
- Egyptian blue or Alexandrian blue: produced from colored glass crushed into fine powder by the Egyptians, it was used for painting and “interior” decoration (mural paintings, etc.).
Alexandria blue, which is also characterized by magnificent shades, is considered to be the first synthetic pigment in the world.
Bonus: when brands have fun with indigo
The Tenue de Nîmes brand has decided to launch a classic pair of white Converse, but hand-dyed with indigo. It's interesting to see how they go about it, even if seen like that it seems like child's play.
Tenue de Nîmes Indigo-dyed Chuck Taylor All Star from Tenue de Nîmes on Vimeo .
Some brands, like Nudie, Arpenter and Selectism, also offer some pieces dyed with dyers' pastel. You will see, the colors obtained are particularly beautiful.
Selectism indigo sweatshirt.
Indigo Nudie t-shirts.
Marinière revisited in indigo, by Arpenteur.
