Indigo


Indigofera suffruticosa

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Growing your own

The Indigofera suffruticosa shown here was grown at Woodburn Plantation in the Upstate of SC, as part of an interpretive project sponsored by the SC Humanities Council. 

Indigo does best when directly seeded in the ground. In the Southeastern US, you can do this as early as January or as late as early May. Do NOT weed or thin until the plants are at least 1.5 feet tall. Indigo does NOT like its feet disturbed, which is why it works better as a direct seeded plant, rather than as a transplant from a pot. 

Common name:      Indigo
Scientific name:     Indigofera tinctoria
Plant family:          Fabaceae (Pea family)
Colors obtained:    BLUE 

Related species: Indigo (the dye) is derived from over thirty plants in at least nine plant families, some of which are very distantly related. Of the Indigofera species used, the most commonly known are I. tinctoria and I. suffruticosa.* For a breakdown of species and plant families, see here.

Part used:     Above ground, green parts

Preparation of dye:     Indigo can be made and used directly from plant materials OR it can be extracted from the plant, dried and then reconstituted for later use. If made and used directly from the plant, there are many ways in which this can be done. This dye prep may vary by species, though that may due to cultural conventions rather than a reflection of the chemistry alone. 

Cultural connections:    Plants from which indigo is derived were and are used in many different parts of the world from Africa, Asia, Europe to North and South America. I. tinctoria and I. suffruticosa were the primary dyestuffs grown in South Carolina (where my first experiments with dye plants began). Because it was grown in upland areas alongside lowland rice cultivation, it transformed the economics of the state in a 40-year period (late 1700’s). To read more about sartorial expression in  Colonial South Carolina life through indigo, see Andrea Feeser’s book on Books & Materials page. TKC dyed the replica skirt on the cover (sewn by Kendra Johnson).  

Interesting bits: Indigo is NOT found in plants. However, the precursor molecules that make the dye, are. It is extracted from the plant during a fermentation process that occurs as the plant material degrades. As the precursors move to form indigo, they do so with help from a naturally occurring aerobic and anaerobic bacterial community

Notes on experience with the dye:

Indigo is a substantive dye, meaning that it adheres to textiles without a mordant, using non-ionic forces. Chemically, it is a reduction-oxidation compound, meaning electrons are transferred from one compound to another. In the case of indigo while  in the vat, it is in a reduced, soluble form known as leuco-white (not really white). However, once oxygen is added, the leuco-white transforms to blue indigo and becomes insoluble, falling to the bottom of the vat (or binding within the cloth as you remove it from the vat. 

Indigo on cellulose (plant fibers like cotton, linen, etc.) doesn’t tend to penetrate the cellulose microfibril very deeply — this is likely because of the tightly wound nature of the fiber molecule — it is rather like a cable of cables. This is the reason why blue jeans can show wear. In effect, a worn area of blue jeans is simply exposing the inner core of the cellulose, which hasn’t been dyed. 

Indigo is laid down on cloth through a series of dips in a vat — rather than a single dip or simmering in a vat. The reason for this is diffusion — the indigo molecules in the vat move into the cloth until an equilibrium of sorts happens with reduced indigo (between the vat and the cloth). At that point, all of the reduced indigo that can penetrate the cloth has — and no more will until the compound oxidizes and locks itself within the cloth. This can sometimes happen in the vat, too — though mostly it takes place outside the vat as one ‘oxidizes’ the cloth. 

Recipes:

There are lots of excellent recipes for indigo out there. Among the most popular lately are recipes that are more environmentally friendly and can be made with somewhat simple ingredients. These ‘organic’ vats use fruit sugars and mineral alkalis to produce similar results as thiox vats or others. The basic idea is 1-2-3. One part indigo; two parts pickling lime; three parts fructose. There are lots of variations out there. I learned from Catherine Ellis, who in turn was taught by Michel Garcia, botanist extraordinaire whom I have never had the pleasure of meeting. 


Key points from all —
1. Using warm water simply makes the reaction happen more quickly. If you are unable to have the vat in a heated environment, it’s ok — the reactions will just take longer. 
2. Different recipes produce different colors in the reduced state. Thiox vats can be light yellow to green, while fructose vats can be almost coppery colored. Getting to know what state your vat is in by color is an important thing to know. THEN, you will know how to adjust it when you’re ready to use/reuse it.
3. Oxygen is the killer to indigo vats by making it fall out of solution. To avoid that: use a narrow necked container (yes, even surface exposure can matter); avoid fast movement while working in the vat; when placing items in the vat, avoid air pockets; and don’t drip your goods in the vat (I typically start squeezing out under the water and continue the squeeze up the side of the vat until all the fiber is out and then swiftly, I place the cloth in a bucket.
4. To repeat a similar note — there is not hard and fast rule for the length of time one should suspend the cloth in the vat. The reasons for this are varied. It is dependent on how thorough is the reduction of the vat; how tight is the weave or design (tightly compressed or stitched areas may need more time; and the time it takes for the concentration of reduced indigo in the vat to be equal to that in the cloth. This principle is known as diffusion, where molecules move from a highly concentrated area to another area of low concentration, basically spreading out of the indigo solution. Over time, you’ll understand when you need to add more indigo and when you need to refresh your vat with either more reduction compounds (sugar, thiox, for example) or alkali materials (lye, pickling lime). 


Literature

*The “I.” designation is another scientific way of denoting the genera — in this case, Indigofera. However, it is only used when the full spelling of the genera occurs first AND when there is no chance of confusion of other genera beginning with the letter in question.  

    © Karen Hall 2015