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Indigo Dyeing - like magic, but science!

I have a new love in my life. Indigo is one of nature's most incredible dyes. it is also one of humanity's oldest dyes and one of only two natural sources of true blue (the other being woad, which contains the same ingredient, but in more dilute quantities). It is not surprising then, that indigo has a rich history and was highly prized by many cultures - that's a story I'll tell you another day.

I will also write more about how to set up and indigo vat for classroom use, and the chemical reaction that takes place when we dye with indigo. For now let's focus on the artistic side of indigo dyeing.

In short, when we ferment an indigo dye vat, we are removing the oxygen from it's molecules. When we add fibres to the vat, the indigo molecules soak into the fibres. When the fibres are lifted out into the lovely, oxygen rich air, the indigo molecules grab the oxygen and become a little bigger. The increased size locks them into the fibres and the oxygenation makes them turn blue.

Indigo dyeing is amazing to watch: a healthy indigo vat is a dark greenish sludgy colour - not a shade you would choose for your handwork. When you remove the fibres from the vat they are also a greenish-yellowy colour but they change to a deep blue before your very eyes! Like magic - but science!

Look at the colour of this sample fresh from the vat...

...compared to this one which has been in the air for a few minutes:

So much fun!

We have been working with a Japanese technique called Shibori, which is traditionally done using indigo dye. Of course you could use this technique with plenty of other kinds of dye, but you would not get the exciting colour change moment and the opportunity to integrate an awesome chemistry lesson.

Shibori means 'to wring, squeeze or press'. It is essentially a very complex and precise form of tie-dye. Fabric is folded, twisted, sewn, bound or clamped into all kinds of shapes and patterns before being submerged in the indigo vat. The purpose of this preparation is to create resist - areas of the fabric that are squeezed so tightly that the dye cannot penetrate so that when it is unbound, there are white areas remaining in beautiful contrast to the blue.

Each technique within the shibori style has its own name and there are many traditional shapes and patterns that the children can research. There are lots of great books about it around. I like 'A Handbook of Indigo Dyeing' by Vivien Prideaux. (I am not affiliated with her in any way.)

When experimenting with the children (or by myself) I use squares of bleached calico - this is inexpensive 100% cotton fabric that is lightweight enough to gather nicely but heavy enough that you could use it in a craft project. Indigo works without any kind of pre-treatment (mordant) but you do need to scour fabric or fibres before dyeing. 'Scouring' simply means washing really well to take out any natural oils or chemicals used in the production process which would inhibit the absorption of dye. If you are dyeing old sheets or clothes (which is a great idea) you probably don't need to do anything to them, if you are using new fabric put it though a hot wash with a scoop of washing soda/ soda ash - that should do the trick!

To create your patterns, fold your fabric into even shapes - rectangles, triangles or squares. (Remember to have lots of conversations about the types of triangles and quadrilaterals you are making.) Then find a way to hold your folds in place. You could wrap elastic bands or twine around it, put binder clips or clothes pegs all over it, clamp a jar lid either side of it - or something else entirely. Another option is to sew rows of running stitches through your fabric and then pull tight so it all bunches up. Tie your thread tightly in a knot so it doesn't come undone in the dye bath.

When you have clamped, stitched or tied the fabric, you need to soak it in water for at least twenty minutes before putting it in the dye vat.

If you choose to use something like Rit dye, you can just follow the instructions on the packet - the end result will be similar. If you are using an indigo vat you will need to use a long stick to give it a firm but gentle stir. You want to mix it up, but not introduce any air bubbles - the indigo molecules won't need to grab onto your fibres if they have already found their oxygen buddies.

You can see how the top layer and the edges of the vat have already oxidized in the picture below but under that is a lovely dark green.

As indigo is fermented, a healthy vat should have a some foam on the top - this is call the bloom. You remove this before dyeing and put it back on at the end.

Slowly submerge your prepared samples into the vat and give them bit of rub - not so much that you dislodge the bindings/clamps but enough to get the dye into all the bits you want it in. Hang around in there for about three minutes and then bring it out into the air.

Watch in wonder as the magic happens and your fabric turns blue. You can repeat this step a few times if you want a deeper colour.

Here is a piece of fabric that we folded into right angled isosceles triangles and then clamped a piece of plywood to each side.

Here it is after is has been dunked in the vat three times, rinsed in lots of fresh running water and the clamps removed

Wooden resists removed:

A little bit of unfolding:

Unfolded all the way:

So simple and satisfying! Here's one that we just pegged:

Ta - daa!

You can see the one above still has a little bit of oxidizing to do.

Even though you rinse the sample before untying/ clamping them, you will need to do it again afterwards. We put the whole lot in a quick cycle in the washing machine with a small amount of powder then hung them out to dry.

After they have been washed and dried, they are safe to wash with other garments - though maybe not your antique white tablecloths.

Once they are all dry, compare the results with your friends, discuss the different techniques you used and make a plan to do something awesome with all your beautiful fabric!

Pro tip when working with children: remind them to keep an eye on the top of their gloves to make sure they don't put their hands too far into the vat. I didn't get a picture of the child who went too deep and the gloves filled up with dye but her whole forearm turned a pretty impressive blue! Fortunately it's not terrible for your skin and it does wash off fairly easily, best avoided nonetheless!

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