Indigo dyeing.

This is a short instruction of how to do an indigo dye; it is recommended that you look up further literature if you plan to do an indigo dye. If you understand Swedish, Sandström and Sisefsky (1981) is greatly recommended when it comes to plant dyeing.

As a chemist, I recommend the general use of glass wares because glass as a material is inert and will generally not be permanently stained or otherwise affected by chemical reactions. This goes ESPECIALLY for handling acids and bases. For the dyeing pot it’s stainless steel or enamelled pots, I myself use stainless steel and a smaller enamelled pot when the occasion calls for it. Iron and copper pots are also usable but will affect the outcome. Avoid aluminium.
I don’t know if this is necessary but I’ll write it anyway; NEVER use any equipment once used for dyeing in cooking. Some simpler things like alum might be easy to wash away but I’m lazy and don’t like meticulous cleaning so I use completely separate sets for everything, measuring and stirring included. I also greatly recommend taking notes on what you’re doing as well as pictures. Combine these two and you will have what is commonly known as a laboratory report. In that way, you don’t have to remember everything you did, for long and how it looked. The human mind is keen on forgetting things very quickly, especially if the process was successful. Writing things down will make it easier to share information or to successfully repeat the process. This is something I myself struggle with as I often wish I would take more informative notes of what I’m doing and why.

An indigo dye needs several chemicals and materials, e.g. table salt aka sodium chloride (NaCl), ammonia (NH3), 25wt% sodium lye aka sodium hydroxide (NaOH), sodium dithionite (Na2S2O4), denatured alcohol (I use T-sprit), indigo. In order to do this as safely as possible it is recommended to read up on every chemical BEFORE dyeing as well as reading the instructions thoroughly! Use the (Material) Safety Data Sheet, something that was mentioned earlier in this post, for each substance if you’re uncertain. If you feel comfortable with all of the chemicals above, how to store them and what to do in case of a spill or other accident, then go ahead.

It would be good to quickly mention the weight percentage of the sodium hydroxide; it’s supposed to be 25wt%, which means that if you want to have a stock solution of 500 gram (approximately 0.5 L since the density of water is 1000 gram/L) then you need 75% of it to be water and 25% of it to be sodium hydroxide. This is easily done by measuring 0.75×500=375 gram of water and then add 0.25×500=125 gram of sodium hydroxide. Keep in mind that this is a exothermic process (gives off energy, in this case heat) and that sodium hydroxide is a base so take care when doing this. If you’re uncertain about what I’m talking about, please read up on some elementary chemistry; it should be covered in most high school chemistry literature. If not, my literature recommendation on basic chemistry is Chemical principles by Atkins and Jones (2013).

In indigo dyeing, there is the preparing of the vat (where the indigo is) and the dye bath (where the vat and fibres are added and the actual dyeing takes place), so look at the instructions for both of these to make sure you have enough material for each step.The indigo vat can be done indoors for several reasons, mainly because of the lack of ammonia. The use of ammonia in the dye bath makes it unsuitable to do indoors unless you have a fume hood or equally efficient ventilation (a kitchen fan is usually not up to standard). Stay outdoors for the dye bath! Plan ahead.



VAT

Material:
Glass jar with a tight shutting lid that holds the total fluid volume of the vat (in this case around 190 ml)
Something to stir the indigo vat with (it will be stained if not glass or stainless steel)
Pot that can be filled with enough water to cover the glass jar
Scale
Stove/heat source
Thermometer

Vat:

10 g indigo powder
Denatured alcohol (I use T-sprit)
165 ml 50°C water
16 ml NaOH 25wt%
10 g Na2S2O4

  1. Put the indigo in the glass jar and add a small amount (10-15 ml) of denatured alcohol, enough so that you can stir the indigo.
  2. Add 165 ml of 50°C water, stir.
  3. Add NaOH.
  4. Gently add the Na2S2Oand stir.
  5. Screw the lid tight shut and immerse the glass jar holding the vat in a 50°C water bath for 1 hour. Put a cork coaster or something similar under the jar to avoid it being in direct contact with the heating source and as such avoid having an uneven temperature in the vat.
  6. Done. The vat will be green-brown in colour.

And there you go. Now you have a vat! You don’t need to use all of the vat at the same time, you can save some for another time. Just make sure to save it in a tightly shut glass jar with a minimum of air in it. Write the amount of indigo and the date on the vat so you know what’s in it and how old it is.

In order to have different shades of blue you can always use more or less indigo, 10 gram would give a somewhat lighter blue.

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Standard setup for making an indigo vat, this is at step 3.
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The green and blue of the vat before step 5.
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A successful indigo vat, step 6.

Dye bath

Material:
A pot/cauldron that can take 16 L of water PLUS additional fabric and/or yarn without being crammed
A stick or something to stir with that is long enough so that you can comfortably stir the pot at the bottom without dipping your hand in the bath
Thick, long protective gloves
Scale
Stove/heat source
Thermometer
About 1000-2000 gram of fibre depending on the wanted colour depth and intensity
(Graduated measure cylinder (mätglas) is not necessary but really good to measure ammonia and sodium hydroxide in)

Dye bath:
16 L water
70 ml ammonia
30 g sodium dithionite
200 g table salt
200 ml vat

  1. Heat the water to 50°C, make sure you have attained a stable temperature as the temperature greatly affects the outcome (deviation at most +/- 5°C).
  2. Add the ammonia (avoid the vapours as much as possible). From now on only use protective gloves when handling anything containing liquid from the bath.
  3. Add the sodium dithionite. After this you should avoid adding air/oxygen in the bath. Stir gently.
  4. Add table salt and wait until the salt is dissolved in the dye bath. If not properly dissolved, the salt will gather at the bottom of the pot and leave dark stains on the fibre that comes in contact with it. To stir the bath in order to more quickly dissolve the salt is fine, just do it carefully in order to avoid stirring down unnecessary amounts of oxygen.
  5. Gently add vat. The surface of the dye bath should have an oily look to it.
  6. Prepare an appropriate amount of fibre (100-500 g) by immersing it in lukewarm water (about 30-40°C) for about 5-10 minutes before dyeing so that it won’t float to the surface when it’s dipped in the dye bath and to avoid dry spots.
  7. Remove the wet fibres from the lukewarm water and remove excess water from fibres by gently squeezing it.
  8. Carefully add the fibres to the dye bath. Avoid creating air pockets in the fibre that will add unnecessary oxygen to the bath or limiting the fibre access by having tangled fibres. Untangle everything and make sure that every part of the fibre is in contact with the dye bath and kept under the surface of the dye bath throughout the dyeing process.
  9. Wait 5-10 minutes. The fibres will look yellow in the bath.
  10. Remove the fibres slowly from bath, avoid dripping as oxidised droplets will add oxygen to your dye bath. The yellow-greenish look on the fibres will slowly turn blue when in contact with oxygen.
  11. Let the fibre oxidise for about 20 minutes to see to what extent the fibre has been dyed.
  12. If wanted, repeat step 8-11 up to a totalt of 4 times for deeper hues and shades.

Use appropriate tools when removing the fibres from the bath. Always wear protective gloves. Protective glasses can also be used if deemed necessary.

Rinse fibres thoroughly after dyeing. Sandberg and Sisefsky (1981) recommends an acidic after wash using acetic acid to increase the general rubbing fastness of the dye.

When dyeing loosely woven wool, it is possible that there will be a shrinkage because of the temperature of the bath. To avoid this, test the shrinkage of your fabric beforehand and add shrinkage allowance accordingly.

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An attempt to photograph the oily surface of a indigo dye bath in step 6, which is a good sign that the vat is working.


Some additional notes on indigo dyeing:

Don’t be in a rush. Take your time, read and think things through. Prepare it in several steps, do the calculations one day and then dye another day. It usually takes me half a day to do one batch of indigo dye and I usually do the calculations the day before.

Not happy with the first result? Then just redo it, an intense indigo dye can save the blotchiest of fabrics.

Make sure you always have some extra fibres for swatches so that you can check that the dye bath gives the colour you wanted. Just remember to wait 20 minutes so the swatches are properly oxidised and thus representative of the end result.

If you get a stain of indigo powder somewhere, just clean it up using a paper tissue with denatured alcohol. But if you get a stain of indigo vat somewhere then there is no helping you. Sorry. To avoid this, be careful and keep a clean working area and remove everything that you could not handle being stained. Wear working clothes, you will get stains on your clothes.

Concerning historical sources of indigo for the 10th century, it is the same dyestuff in both woad and indigo; indigotin. According to my understanding, it is at the moment not possible to distinguish the indigotin source in older fabrics and findings even though it is probable that the main source of indigotin in the Nordic countries during the 10th century is woad. As an example, the indigotin found in the Mammen grave is said to be either woad or indigo (Hägg, Inga et al., 1991). On a different note, madder is also found at Mammen even though there are no evidence of the cultivation of madder in Scandinavia at that time. The dyestuff, procedure and result is the same for both woad and indigo; the main difference right now is that indigo powder is a lot cheaper than woad powder which unfortunately makes a lot of difference for me. But then again, the rest of my reenactment gear is not on the level that the breaking point of its authenticity would be the origin of the dyestuff. But when it is, I’ll do something about it.

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A typical indigo dye setup, stained hands are optional.

Currently, I think that the trickiest part with indigo dyeing is knowing when to stop. At some point, you will not have enough indigo and/or too much oxygen in the bath and that will make the dyeing uneven or without effect. But exactly where that point comes is something I’m currently trying to figure out. Experience is key.

Keep in mind that the above, numbers and all, is more what you’d call “guidelines” than actual rules.

Happy dyeing y’all.

 

References

Atkins, P.W., Jones, L. & Laverman, L. 2013, Chemical principles: the quest for insight, 6th, International edn, W.H. Freeman and Company, New York.

Hägg, Inga, Gräslund, Anne-Sofie, Jansson, Ingmar, Iversen, Mette, Näsman, Ulf & Vellev, Jens (red.) (1991). Mammen: grav, kunst og samfund i vikingetid. Højbjerg: Jysk arkæologisk selskab

Sandberg, Gösta & Sisefsky, Jan (1981). Växtfärgning. 5., [omarb.] uppl. Stockholm: Norstedt.