Experimenting with indigo vats

Natural dyeing is a big interest of mine, it really is the corner of the textile world where I really can use the fact that I am a biologist, and where my knowledge about plants and chemistry come in handy. I was taught the basics by my grandmother about ten years ago and have been experimenting since.

I have mostly dyed with native plants, mushrooms and lichens (and madder, of course), but since I came to Capellagården I have also added indigo to the palette. There is much to say about indigo, but now I want to talk a little about the dye process. I'm afraid it will be a rather long text, so skip to the end if you want to see the results of my current experiments.

Contrary to most natural dyes Indigo is a reductive dye (kypfärg in Swedish), which, somewhat simplified, means that the indigo dye vat, besides the actual indigo also needs a reducing agent that takes away oxygen from the indigo molecule, thus reducing it to a watersoluble state that can stick to the fibre you dye. In reduced state, the dyevat is yellowish green, and when you lift the fibre out of the dye vat, exposing it for the oxygen in the air, the molecule changes back to indigo, turning blue and sticking hard to the outside of the fibre.

The most common way to do this, these days (or since indigo dyeing was rationalised into a modern industry) is to add sodium dithionite (often called sodium hydrosulphite, in swedish, natriumhydrosulfit) to the dye vat. It is a white, bad smelling powder that acts as a strong reducing agent in water. It works really well for this purpose, but it is also a chemical which one might want to avoid since it is harmful to breathe in or get on the skin, and should not be poured down the drain. To keep the vat alkaline enough for the reduction process to properly take place sodium hydroxide, and/or ammonia (natronlut och ammoniak på svenska) is also commonly added added to the vat, and these chemicals are common but none the less harmful to the skin, and in case of ammonia harmful or toxic to both humans and other organisms depending on the concentration. To dye in this way, you need to know basic handling of chemicals, use gloves in the vat and generally be careful.

In the old days (and still in some places) indigo was obtained by fermentation of the leaves of different indigo producing plants (or with indigo powder extracted from this kind of fermentation), and the reducing process was helped on the way by adding different natural ingredients such as rotten fruit, bran or pee (there are thousands of ways). It was and is a complicated process, that took time to master and a skill that was almost mythical and that only certain dyers knew about. Indigo itself was hard to obtain since the plants had to be grown and taken care of and the dye content of the plants is low. With the chemical vat and the invention of synthetic indigo, almost anyone can dye with indigo - and that is, I think, in some ways a good thing, because it is a wonderful experience. (I don't think industrial indigo dyeing is a good thing though.. google it if you want to know more.) However, if you had that experience some times and start to understand the process, I also think you should start to think a bit deeper.

I'm not generally opposed to the use of chemicals but if it is possible to do without I'd rather, in dyeing as in anything. For me the act of dyeing and working with textiles is an act of sustainability, and frankly, the chemical dye vat is not a sustainable thing. It also totally lack the charm and inpredictability of dyeing in a more natural way, and it is also, in my opinion, a bit boring. You just measure and pour.. just as if you were mixing a colour of any kind. No magic, just chemistry. It is not in my opinion, natural dyeing.

Now we come to the reason why I started to write this post! I have started to experiment with other kinds of dye vats with indigo, to be able to get these gorgeous blues without all the nasty stuff. My dream would be to make indigo from scratch, from the plant so to speak, and this I will try this summer - I plan to grow woad (Isatis tinctoria) which is a indigo producing plant that was traditionally used in Europe and is suited to our climate. In the mean time however, there are other ways.

Indigo stock solution

I have been experimenting with the so called "Fructose vat" lately (google it!). Here you use indigo powder (natural or synthetic which both can be obtained over the internet, I vote for natural of course), and for reducing agent you use fructose, common fruit sugar, that you can buy in you local food store. For keeping the alkalinity of the vat you use slaked lime (Calcium hydroxide - kalciumhydroxid eller släckt kalk på svenska) which is a common constituent of mortar or plaster, easily obtained from a hardware store. I got hold of the necessesary ingredients and started making a vat. Here is a good link to a general description of how you do it - I used together with some other websites and books. Most recipes use dry slaked lime, but the one I had was wet, so I had to improvise since the weights are different.  I was amazed to see that the reduction actually was taking place - it was working! The water turned deep green and a copperish sheen (hard to see on the pic, I know..) was building up on the surface.

 When the vat was prepared I test dyed some old cotton sheet fabric, and it turned out very light. Not at all the deep blues I was used to with the chemical vats I tried before. I could also see some non-reduced pigment floating in the vat, so the reduction had not fully happened. I added more sugar and lime and waited. After an hour or so, I got a little bit deeper shades, but still very light. Then I decided to try multiple dipping.


One of the bad things with the chemical vat is that it is harder to obtain darker shades on the fiber by multiple dippings. This because the chemicals are so strong that they dissolve the indigo already fixed on the fibre. With the fructose vat it works well!

The fabric squares on the left in the picture below are dipped (bottom to top) 1 -2-4-and 8 times.
The one to the right is dipped whenever I had time, but not the whole piece, creating a gradiating colour. I probably could have gotten even darker colours, but due to things not concerning dyeing I had to pour the vat out before it was exhausted.

In descriptions of old time indigo dyeing, one often reads that they had to dip the fabric or yarns maaany times to obtain the blue colour they needed, and now I can really see why :).
I think. however, that  I would be able to get a stronger initial colour if I could get the reduction to go more complete and keep the right pH of the vat - something I had no means of measuring this time.

Now I have ordered pH -measure paper and is ready to try again! If I find a good way - I'll publish the recipe here!

A Wettex dish cloth dipped multiple times in the fructose vat