Indigo can be used to dye any natural fibres. It gives beautiful shades of blue and is definitely one of our favourite natural dyes to work with as the process feels so magical.
The colour achieved depends on the type of vat, the concentration of indigo, and the number of dips.
Indigotin (the dye component of indigo powder) is insoluble in water, so to use it for dyeing it must be reduced to a water-soluble form.
All indigo vats need three things: 1) Indigo 2) A reducing agent 3) A Base.
Reducing agents are usually chemicals but we can use sugar instead.
A reducing agent lowers the oxidation state of the indigo molecule, transforming indigotin into leuco-indigo — which is soluble in water at room temperature. If we just add powdered indigo to water it will remain in pigment form, suspended but not dissolved.
In order for the reducing agent to act on the indigo, a basic environment is required. Chemically speaking, a base is the opposite of an acid. The reduction of indigo requires a basic (alkaline) solution. A recommended base for an indigo vat is calx (calcium hydroxide) also known as lime, pickling lime, or hydrated lime.
When the indigo is dissolved, the dye bath is a greeny-yellow colour. On the top of the vat, air oxidizes the indigo, resulting in blue indigo pigment. Resting on the bottom of the vat is the sediment consisting of any undissolved indigo, reducing agent or base.
Ahead of your cotton fabric you need to scour it. This removes any oils which may be sitting in the fabric. You can do this by washing in a washing machine at 40 degrees with some ecover detergent.
The Fructose Vat
Don’t forget to scour your cloth or yarn before dyeing.
For a vat of about 8 litres
— 30 g (1 oz) powdered natural indigo
— 90 g (3 oz) fructose
— 60 g (2 oz) calx (calcium hydroxide)
Fill a 10 litre (2.5 gallon) stainless steel vat 3/4 full with hot water.
Add the fructose and stir to dissolve.
Add the indigo to the vat. Sprinkle on the surface of the vat and stir in until well mixed.
Add half the calx (reserve the second half if you find you need to raise the pH). Sprinkle on the surface of the vat and stir the vat gently. Do not do too quickly. You do not want air in the liquid. Wait for a few minutes. Then stir again. Repeat this stirring three or four times.
Heat until the liquid reaches 50°C (120° F). You may then turn off the heat. In about 45 mins - hour the vat develops a bronzy surface and a small dark blue indigo flower. The interior of the vat will be a clear yellow green.
Fructose can be used to quickly build a strong vat. However, fructose vats can also collapse easily or be difficult to revive. For this reason, we recommend making a smaller vat when using fructose. A smaller vat also uses less indigo and so (if your vat collapses) there is less dye wasted.
Note: Sucrose (refined table sugar) is not a reducing sugar and so will not work.
In order to achieve the shibori effect on our knickers we used natural rubber elastic bands wrapped around each section of the knickers. Take a look at our instagram reels to see this process in action!
Enjoy experimenting with Indigo.
Tag us in your experiments @bedstrawandmadder