Perhaps the most mysterious of pigments is indigotin. It is also the most ancient known one. in 2016 archaeologists uncovered several scraps of indigo-dyed fabric at the Huaca Prieta ceremonial mound in northern Peru. They were believed to be about 6,200 years old.
From all the pigments it is surely the more complicated one to use because both extracting and applying the pigment from the leaves requires a fair amount of knowledge, experience and understanding.
When we see Dyer's greenweed it is easy to understand how we create yellow from it, the flowers are yellow, you throw them in hot water and you get a yellow dye that colours your fabric...yellow. But with indigotin we can not see the secret blues that are hidden in the leaves, and when we have the pigment extracted, we still need to make an indigo vat to use it.
The Indigotin Extraction Process
To extract indigotin so we can store it (almost) indefinitely) we need to transform indican (a pale green organic compound present in the leaves of Indigofera, Isatis and Persicaria plants) into indoxyl and then into indigotin. To explain this complicated process I have made a small illustrative video.
Do we always need to extract indigotin? Not exactly, you can also use the entire leaf and do a direct application on fabric.
Direct application of indican on fabric.
It is possible to do a 'all-in-one' technique with either fresh indigo leaves (see this blog) or with dried indigo leaves.
(dried indigo leaves of Indigofera tinctoria)
When you use green indigo (see also this blog), you go from indican to indoxyl and then to indigotin straight on fabric with water. So the indigotin is already trapped in the fabric while you work the sludge.
The green is formed by the flavonoids that are also present in the leaves, fresh or dry. Yellow + blue = green.
Hapa Zome
The same thing happens when you are pounding fresh leaves with a mallet straight onto fabrics, but because you are not using heat and water, the flavonoids do not get released as much so the result is more blue.
Hapazome is a Japanese word meaning 'leaf dye', given to the process of transferring the natural pigments from leaves and flowers onto fabric or paper to create a botanical image.
A word about Indirubin.
Besides indican, the leaves of indican bearing plants also contain indirubin. You can extract this reddish purple by using hot water (70ºC+) on fresh or dried indigo leaves in a slightly alkaline environment.
Indigo Plants
So which are the plants that contain the indican we need to form indigotin? There are many plants, but indican levels vary per species, and also per year and per season. Lastly, the indigotin yield depends greatly on the chosen way of extraction. Drying indigo loses up to 50% of the indican. 50% indigotin in indigo powder is considered excellent, the best and most expensive extracts have a level of 74%. the higher the indigotin level, the less powder you need for a vat.
In the textile industry, natural indigo powder has been mostly replaced by synthetic indigo but for craft dyers and small fashion products it remains relevant as ever. Stony Creek indigo growers in the USA are working on some wonderful projects to go back to true denim blues.
The better known species of indican rich plants are the Indigofera species, from the pea family Leguminosae. There are about 750 species in this category, distributed across all tropical areas. Besides indican their phytochemistry has over 200 compounds, used in traditional natural medicine. It will be too much to go into all of these plants, so I picked the ones most interesting and some fun unknown species.
Indigofera tinctoria, the most used indigo plant. Grown widely in India and in lesser quantities in Bangladesh. We have this indigo in the shape of small square Indigo cakes from a reliable supplier in India. The luscious green shrubs have a beautiful leaf shape and grow, well, like peas. You can harvest a field more than once in one season.
Other subspecies of Indigofera are grown in Asia but specifically in Indonesia. The great advantage of these Indigofera species is that they grow organically: they do not need any insecticides to ward off pests. DekelDyes has two types of this indigo as well as a blend. All come directly from Eyster who owns an indigo farm on Java, where they grow indigo mainly for the use in indigo batik art.
Indigofera arrecta, also known as Natal Indigo or Java Indigo. Grown in Bangladesh, Indonesia and in some African countries.
It's a tropical small shrub of herb growing up to four meters in height with slightly hairy leaves. I. arrecta is also used as a cover crop and a fertilizer.
Fun fact; the twigs are used for cleaning teeth.
Indigofera Longeracemosa. Indigofera longeracemosa is a woody herb that can grow up to 2 meters tall with slender red-brown stems. It is not a very well known crop, but is considered a superior source of indigo. Today it is still grown on a small scale around villages in Indonesia and Madagascar.
Fun fact; the root of Indigofera longeracemosa is considered an antidote for snake poison.
Indigofera suffruticosa, Guatemalan indigo. Grown on haciendas in South America (El Salvador) and also in Indonesia. The leaves are smaller than I. tinctoria, and it has a high yield of indigotin. We have I.suffruticosa available in a blend with Indigofera arrecta.
Indican bearing plants, not from the pea family;
Persicaria Tinctoria also known as Japanese indigo and Dyer's knotweed (Polygonum tinctorium), a member of the buckwheat family. It is grown in Japan, China, and grows well in the warmer areas of Europe. David Santandreux has some experimental fields in France and I know of other initiatives to grow it in the USA on a commercial scale.
My friend Hagar grows Persicaria in her own garden, and gifted me with some plants to work with, she makes beautiful quilts with them you can check out her work here.
Isatis Tinctoria, woad, also known as Asp of Jerusalem (I do not know why) and Pastel in France.
In France you can see woad growing along the side of the road, with the festive yellow flowers going up from the green rosette to one meter tall.
Woad was the only European source for blue, until the introduction of imported indigo pushed it slowly but surely to the sidelines, making it no longer economically viable to grow.
When it was at its' peak, the estimated export in France alone was 100,000 bales exported annually. The monoculture of “blue gold" caused depletion of the soil and contributed to famine.
Woad would traditionally be fermented in balls or heaps, a labour intense work that was certainly not giving the best yield of indigotin, so you would need a lot of it to make a woad vat. Fun fact; the woad fermenting process produces a smell so disgusting that in Tudor times a Royal decree was issued against working with woad in a three mile radius of the palace.
Today the indigotin is extracted from woad with methods similar to the way it is extracted from Indigofera and Persicaria, giving it a fine powder that is not less potent than any regular indigo powder and you prepare it the same way as the indigo vat, just a little bit less reducing agent.
In China woad is known as Banlangen and used in traditional Chinese medicine against flu and cold symptoms. The Bai people in South West China have a longstanding tradition of dyeing with woad.
Now that we have the indigotin pigment in the shape of indigo powder, how do we transfer the blue pigment to fabric? Unlike other phyto-pigments, we can't just make a dye pot with water and indigo powder and hang fabrics in. The indigo itself is insoluble in water and needs a process called a vat. There is a good step-by-step instruction here on making an indigo vat.
With thanks to Ian Bowers for fact checking this article.