Indigo and a Simple Vat

19 June 2006

indigo ferns(sm) .jpg
This is my shibori on cotton T-shirts. Indigo and shibori are natural partners. The Japanese shibori still being made in Arimatsu Shibori is mostly indigo on white cotton. I am including some simple instructions for making an indigo vat. This article was orginally written and published as a SHOPTALK article in the newsletter published 4 times a year by the Surface Design Association. Indigo is not a simple subject so I expect to revisit it.

indigo rosettes(sm).jpg
Indigo is an ancient and unusual dye stuff. Egyptian Pharaohs buried their dead in indigo dyed cloth. Indigo has a long history in Africa, China, Japan and India, where it is recorded in four thousand year old Sanskrit documents. Ancient Andean textiles are even tie-dyed with indigo. Several plants, indigo and woad, produce the dye stuff in their leaves, which are green. The extraction of the dye stuff from the plant is a long and complex process.
Very few natural blue dye stuffs exist, indigo is the only commonly used blue natural dye. Both natural and synthetic indigo are still in use today. The synthetic indigo is cheaper and therefore used to dye your jeans. Natural indigo is contaminated with other, but closely related dye stuffs, giving a richer palette which shibori dyers appreciate.
The blue indigo is insoluble in water and therefore can not dye cloth. A reduced form of indigo, sometimes called white indigo, is soluble in an alkaline solution. This reduced form of the dye is readily oxidized back to the blue form by exposing it to the oxygen in the air. Once the insoluble blue indigo is in the cloth, it is there to stay. It will dye any fiber you can get water into: cotton, linen, wool, silk, etc.
Neither the dye bath nor the fiber in the dye pot will look blue. Once the fibers are removed from the dye bath and exposed to the air they start to turn blue. After it has completely turned blue, the fibers can be dipped back into the dye bath to get a darker color. Many dips are required to build up a luscious dark blackish blue.
This modern chemical method uses either sodium hydrosulfite or thiourea dioxide to reduce the blue indigo to the leuco-indigo . Handling the powdered metallic dust for the zinc-lime vat is now recognized as hazardous and the fermented vats are too slow and temperamental, so this is a safe and reliable vat, easy for a novice indigo dyer.
Il use thiourea dioxide as the reducing agent, if you use sodium hydrosulfite, which is much weaker, you will need to use more.
I prepare a indigo stock solution and a vat, free of oxygen, and then combine the two. In the stock solution the indigo will be reduced and dissolved, so that we don’t have to worry about that in the vat. The stock solution is very alkaline, because it contains lye, assuring the dissolution of the solid dye. The vat should not be that alkaline because these extreme pH could damage the fibers. So in the stock we have the idea conditions for the rapid reduction and dissolution of the indigo and in the vat we have good conditions for the fiber. We will add small amounts of the stock to the vat initially and then as it gets consumed from the dye bath. We will also have to maintain the conditions, pH and oxygen –free state, of the vat.
I use:
Indigo, synthetic, microperle is the easiest to dissolve and use
Lye – found in the supermarket with drain cleaners, used to prepare the indigo stock solution
Thiourea dioxide or sodium hydrosulfite to reduce the vat
Soda ash – to raise the pH of the vat
optional-pH paper – to measure the pH of the vat (for the range pH >8)
Plastic containers are cheap and inert to these solution as the lye and alkaline solutions are very corrosive and will react with glass and any metal except stainless steel.
Prepare Indigo stock
Dissolve lye. Slowly add 1.5 oz. of lye to one cup of water. The solution may get hot, so go slow. The lye and its solution are very corrosive to human flesh, so wear goggles, gloves and work carefully. Clean up any splashes or spills with lots of water.
Dissolve indigo. In a 1 quart container, place 2 oz. of indigo powder. Add enough water to paste up the dye. Then add the dissolved lye, carefully. Then fill with warm water. Sprinkle 1/4 oz. of thiourea dioxide on the top and stir until dissolved. Let stand 1 hr. or more until there is yellowish solution beneath the blue surface. A drop of the yellowish solution should turn blue as it trickles down the outside of the jar in 20-30 seconds. This process can be hurried along by heating in a water bath to 120°F (never more than 140°F). If it only turns greenish yellow add some more thiourea dioxide, a 1/2 teaspoon at a time and wait another 1/2 hr. Cap tightly. Will store indefinitely, will turn all blue if too much oxygen gets in.
Prepare the vat
Any size vat can be used but a 13 gallon kitchen garbage size is convenient, a lid is nice for a vat that will be used for a long time. Fill with warm water, and stir in 1/2 cup of soda ash until dissolved. Test pH, it should be 10 or greater. If not add more soda ash. When the soda ash is dissolved and the pH satisfactory, stir in 1 tablespoon of thiourea dioxide. This will react with the oxygen dissolved in the water. Let sit 30 minutes or more. When you are ready to dye add, with a great deal of care, 1/4 cup of the indigo stock solution.
Dyeing with the indigo vat
Prewash or scour all goods.
Wet all goods thoroughly before dyeing in indigo.
Remove surface scum from the vat to prevent spotting.
Carefully introduce the goods into the vat. This is when oxygen gets added to the vat, so do it carefully and slowly. Move the goods under the surface for 10 min. Avoid the sediment on the bottom.
Remove the goods, slowly and carefully. Catch drips in a separate tubs, they can add a lot of oxygen to the vat. The goods should have a yellowish cast.
Let the goods oxidize by exposure to the air. At least 30 min., overnight is best. You will see the yellowish color disappear and blue take its place.
Dip and air again and again until you have the color you want.
Let air for 24 hrs., then wash. Wash until no more blue comes off.
Neutralize by soaking in a vinegar bath for 10. min. or in a tannin bath (also known as hot tea) for 10 –30 min.
Maintain the vat
With normal use the indigo will be consumed and oxygen will be introduced.
When the blue color does not darken, or you can see that there is no more indigo in the vat, you will need to replenish the indigo. Add indigo stock a tablespoon at a time.
When the vat is too blue, you will need to reduce the vat, because it has too much oxygen. Add 1 teaspoon of thiourea dioxide and wait 30 min. for it to reduce.
Dyeing with indigo is a complex process, probably the hardest dyeing I do. I feel very humble when I see what the ancient dyers accomplished with indigo.
Q My vat no longer works, how do I fix it?
A Many things can go wrong with a vat:
If the pH is too low (less than 10) the indigo will not reduce, no matter how much thiourea dioxide you add. You will need to add more soda ash to raise the pH and get the vat working.
If the vat is sharp yellow below the blue surface ( instead of the normal yellowish-green) the pH is too high and you will need to lower it by adding a drop or two of lemon juice or vinegar.
If you have too much thiourea dioxide ( or other reducing agent) you will not be able to build up dark colors because some of the indigo on the cloth will dissolve each time you introduce the cloth. Whip the vat a bit to incorporate some air and use up the excess reducing agent.
Q My dark indigo dyed cloth rubs off blue on everything, how can I prevent this?
A Indigo is very wash fast but has a tendency to crock (rub off) . The crocking can be reduced by slowly building up the layers of indigo, long oxidation periods and washing between each dip. The Japanese will use 30 dips to build up the darkest color. If you don’t wash between dips, do a final wash with hot water and an aggressive detergent such as Synthrapol, until no more blue comes off, then neutralize.
Q I like the pale turquoisey blue you get with the first dip, but it seems to disappear with time, what did I do wrong?
A Nothing, one dip indigo is not stable and tends to fade. To get a stable pale color add very little indigo to the bath and dip three times. Neutralize and wash.
Q How long can I keep a vat?
A Indefinitely. You just have too keep adjusting it. If it sets for a long time with out use it will all oxidize and you will need to add reducing agent, thiourea dioxide, before using.


5 Responses to “Indigo and a Simple Vat”

  1. mary sprake Says:

    I am trying to find a fail resist recipe for a rice resist paste that will take many dips of indigo – any ideas please


  2. glennis Says:

    thanks for the very clear instructions for indigo dyeing. i just took a workshop that peaked my interest in indigo but unfortunately the teachers had very little knowlege on the subject (even though the class was to include indigo dyeing!). i owe you for the wealth of information you provide-
    next step- order materials for an indigo vat and start practicing!


  3. Eva McGehee Says:

    Dear Ms. Brito,
    thank you for writing such a wonderful book which inspired me to try shibori. Unfortunately I am not doing well. Starting with simple rings using kamosage knot, the dye is seeping under the treads. I paint on Habotai 10mm with brush using Jacquard liquid silk dyes (green label) wet-on-wet. For treads I tried button-hole, cotton quilting and nylon.
    I moved this comment to , Troubleshooting.


  4. Hello and thanks for the information about reducing agents…(dye list)
    In this section about the indigo vat, you are not keeping the vat heated??
    I am dyeing loose wool fibre so I’m not sure if it should hang around without being uneutralized for too long…
    I have the ph at about 9… At 11 it kills the wool.
    I keep the vat at 50degrees C.
    I’m thinking about repeat dips…
    What do you suggest??
    This is a great blog, thanks… Rod


  5. Hi Karen! Iv gotten into dyeing these days (never thought that i would ! ) im going to read all your posts on dyeing now! Just wanted to say hi and also let you know (in case youre not aware) that pictures from your old posts such as this one, are not loading – im going to read them regardless – take care!


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