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Indigo Natural Fermentation Vat

Indigo is a dye different than any other. It is dyed through a living fermentation process that does not require any mordant.

The process “reduces” the Indigo, changing it from blue to yellow. In this state, it dissolves in an alkaline solution. The fibre is worked in the solution, or “vat.” When brought out to the air, it is a bright green. Slowly the air changes it to the beautiful deep and rich blue of Indigo.

Indigo in some form is used in all traditional cultures, for it is the only clear and fast natural blue. Indigo dyeing was one of the first speciality professions. Yet it is easy to keep a home pot going, and most colonial homesteads had one. This recipe is the one most commonly used for home dyeing. It contains no harsh chemicals nor toxic metals. It can be used to dye any natural fibre.

An additional beauty of dark Indigo is that when ironed or pounded, the blue cloth takes on a beautiful coppery sheen – the same sheen that is seen on the well reduced Indigo vat, when it is ready for dyeing.

The Natural Fermentation Vat

NOTE: This process requires advance preparation of about one week. The amounts are weight ounces, not volume ounces. Below is what the indigo vat should look like at the end, when it is ready to use.

  • 4 oz. ground Indigo
  • 2 oz. ground Madder
  • 2 oz. wheat bran (buy at any health food store)
  • 12 oz. washing soda (“soda ash”)

Combine these ingredients in about a three gallon pot of warm water. Always add these amounts in proportion. A larger vat can be made, for example with: 1 lb. ground indigo, 1/2 lb ground madder, 1/2 lb ground bran and 3 lbs washing soda in about a 10 gallon plastic tub. However, I advise starting small, till you are comfortable with the process. The size of the pot is determined by the amount of fobre you need to dye at one time. A three gallon pot is good for yarn skeins of 4 to 6 oz., while a 10 gallon or larger tub will be needed for yards of fabric.

WARMTH: It is necessary to keep the vat warm, but not hot, around 100 – 110° Fahrenheit. It is the same temperature for raising bread or making yogurt. It should feel pleasantly warm to the hand.

To keep it warm, a light bulb in a reflector can be put under the vat, with a blanket over it to keep in the heat. (See illustration, next page.) In a warm climate no additional heat is needed, but be sure the vat is out of direct sun so it does not overheat.

TIME is very important. It takes time for the vat to ferment and it does no good to try to rush the process. The first time, it takes about a week for the vat to ferment and be ready to dye. With “renewals” the time needed is a bit less, four or five days.

It takes time to do the dyeing. The fibre is “dipped” several times to build up a dark colour, with airing between each dip.

The vat itself lasts a long time. I have had my current vat over fifteen years. In traditional cultures there are vats over 100 years old. The vat is “renewed” with more Indigo and the other ingredients in proportion, whenever the dye value weakens. Then let sit a few days to re-ferment. Indigo dyeing by this natural fermentation method is a slow-steady process. It is good meditation.

Stir the vat once a day. The idea is to integrate the undissolved Indigo, madder and bran that settles to the bottom, back into solution. And to do this without incorporating air into the vat. So stir gently.

Keep the vat covered. Air is the enemy of a good Indigo vat. The level of liquid in the pot should just allow room for the yarn dyeing, without spilling. The less air between surface and lid the better. I use a domed lid, turned upside down. If you leave more than 2″ of air at the top of the vat, it will not reduce properly.

The vat is ready for dyeing when:

  • It develops a coppery film on the top of the vat.
  • The liquid, lifted carefully in a glass jar, will appear green.
  • A test piece of fibre or paper will emerge green and turn blue in the air.

Now is the exciting time to begin Indigo dyeing!

  1. Wet your fibre out very well in warm water. It must be well wet out. Any air remaining in the fibre will oxidize Indigo in the vat, and this must be avoided.
  2. Put on rubber gloves! You don’t want to scare people with blue hands; also the strongly alkaline vat may irritate your skin.
  3. Enter the fibre (yarn/fabric) into the vat very carefully, to avoid adding any air to the vat. Now the fibre must be “worked” in the vat, under the surface. It should not be stirred, but with your gloved hands, gently, slowly and deliberately squeeze the liquid through the fibre while you hold it under the surface. Any time you break the surface you introduce air into the vat and this you do not want to do.
  4. After you have worked it several minutes, carefully and slowly raise it out of the vat, squeezing the excess Indigo solution back into the vat. Do this squeezing as close to the surface as you can, as dropping liquid will bring air into the vat.
  5. The fibre should be a bright clear green. It will start to turn blue in the air immediately. Lay it out on newspaper and let it air for 20 minutes. Repeat the dips up to five times for dark Indigo Blue. Air between each dip. For lighter shades, fewer dips are needed.
  6. Rinse well. Then leave the fibre to air overnight. Soak and do a final rinse in the morning.

The vat lasts indefinitely. It is begun with a certain amount of Indigo, and all other ingredients as given, in proportion. Dyeing is begun, with the darkest colour dyed first, then medium, then lights. Between dyeings the vat must rest overnight or an extra day. This is because, during dyeing a certain amount of the Indigo is oxidized in the vat. Allowing it to rest lets it re-reduce that Indigo. An oxidized (blue coloured) vat won’t dye well. The Indigo colour will only wash out and rub off too quickly.

When the vat is “exhausted”, and will only dye light shades, it is time to renew it. All ingredients are again added, again in correct proportion. The vat is let to ferment for several days, and is ready to dye when it shows the proper signs. In this way a vat can be kept going for many years.

If one wishes to rest from dyeing for several weeks, simply turn off the heat source, and keep the vat cool for that period. Stir it vigorously on occasion. When ready to dye again, warm it up, renew it with the ingredients, and proceed as before.

It is not good to leave a vat unused for too long, as it is a living process and may then get cranky about starting up again. Also it is important to exhaust the vat before leaving it, or it may over-ferment and ruin any Indigo remaining in it.

Over time a deposit of sludge will develop at the bottom of the vat. You may want to gently lower a screen into the vat before dyeing, to keep your fibre from pickinging itup during the dye process. Be sure to remove the screen after the day’s dyeing, so you can stir the vat before closing it.

For greens, dye you fibre Indigo first, then rinse well and overdye with alum mordant and your chosen yellow dye. For purples, dye the Indigo first, rinse well, then mordant and dye over with any red dye.

The indigo vat is very alkaline. It is important to rinse out all the alkalinity. Just to be on the safe side, I always double rinse my indigo dyed textiles. First I rinse well just after dyeing, then I let air overnight. Next day I soak in two successive waters for about an hour each time, rinse again, wring and dry.

Squeeze solution through yarn for best penetration. Always work under the surface of the vat. Always wear rubber gloves.

More About Indigo

Indigofera is a legume. The plant looks similar to alfalfa, but is usually larger. It is an excellent rotational crop for increasing soil fertility. In southern Mexico, where some of the current Indigo of commerce originates, it is naturalized and grows in fallow fields, so no effort is spent cultivating it.

Indigo dye must be prepared from the fresh plant in an exacting and elaborate process that takes about a month. The Indigo plants are harvested and brought to a central location. They are soaked in water and allowed to ferment. This separates the dyestuff from the plant. The solution is then beaten to oxidize and precipitate the Indigo. Excess water is poured off and the sludge is dried. This sludge, packed into balls or patties and fully dried, is the Indigo dye of commerce.

This Indigo comes to us in the form of a hard, dark blue coloured cake. It must be ground to be used for dyeing. Very small amounts can be ground in a mortar and pestle. Use a bit of water to facilitate grinding and keep down the dust. A Corona Corn mill is what I use. Meat grinders also work. A zip-loc baggie cinched over the grinding plates catches all the powder and keeps blue dust from getting everywhere.

In most traditional cultures, the colour(s) of ones clothing indicates ones status or class. Indigo blue has long been associated with the less than aristocratic classes. Indigo blue has still the association of “The Working Class”. We use the distinction as “Blue Collar Workers” and “Blue Jeans”. These clothes were originally dyed with indigo. In the past, Indigo has been a prolific dyestuff. It is relatively easy to grow and dye, and is quite fast. It withstands well the many washings that work clothes require.

In most cultures, Indigo dyeing is or was a specialty. The dye process is unique, and the facilities require a stable set-up. Vats made of great clay pots set in the ground are commonly used in warmer climates. If more heat is needed, pits for burning charcoal are placed between clusters of the vats.

Indigo dyeing is practiced today in Japan, Southern China, Tibet, India, Indonesia, Indo China, Africa, especially Nigeria, Southern Mexico and Guatemala, and it has recently been reintroduced to Turkey. Traditional fermentation methods are used. However, many of these cultures now use synthetic Indigo, manufactured from coal tar or petroleum.

Natural Indigo contains several related dye chemicals that give different shades of blue. As much as twenty percent of the dye may be a violet tone called Indigo Red. These complexities give Natural Indigo nuances and depths that cannot be achieved with the synthetic substitute.

An additional beauty of dark Indigo Blue, is that when ironed or pounded, cloth so dyed takes a coppery sheen – the same sheen we see on the top of the well-reduced Indigo vat.

For more detailed instruction and recipes for colors, please purchase the book Brilliant Colours with Natural Dyes.

2 thoughts on “Indigo Natural Fermentation Vat”

  1. Roben Campbell says:

    can the recipe for indigo using washing soda be used on wool?

    1. Aurora Silk says:

      Hello. Yes, the Natural Fermentation Indigo Vat can be used with wool. Thank you for your question.

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