Indigo Fructose Dye Vat

Indigo Dye Yarns
Indigo Dye Yarns

This is another method for making an Indigo Fructose Dye Vat that I developed using ideas from Michel Garcia’s 1-2-3 Indigo vat and J.N. Liles Indigo dye recipes – using Calcium Oxide – CaO as the Alkali

For many years, I followed the traditional indigo dye vat methods using large 5-10 gallon dye vats, trying to keep the dye vat warm and going, by using various heating systems such as heating the large metal pots on the stove, or beer brewing heating pads, placing the vat beside a heater and wrapping it with blankets. I often had trouble getting the vat to ferment fully and had to discard the vat and start again. I found that using the large vats, I could not see what was actually happening to the vat so it was difficult to make adjustments and what to add to correct the vat: more sugar, more alkali or more dye.

As I use slow cookers for much of my other dye work, I realized that I could also use the crock pots for the indigo vat as well by using a large glass jar or glass beaker as the vat. I placed glass beaker inside the crock pot, and filled outer slow cooker with water. This acts as a double boiler. The heated crock pot keeps the dye vat warm. I do have to watch the water level in the crock pot carefully as I am not able to place a lid on it, so the water can evaporate quite quickly from the slow cooker.
The glass beaker also also allows you to see what is happening within the vat.

A 2-3 litre beaker will allow you to dye approx. 50-100 grams of yarn at a time. If you wish to dye a larger amount at the same time then you will need to use a large bucket in order to fit the material and an alternate method of keeping the Vat warm.

Indigo Blue
Indigo blue dye is produced by a chemical reaction in the dye vat. The vat solution has to be in an alkali state. Fermentation of the vat occurs with the addition of a sugar/fructose solution.
As the fermentation process takes place, one of the Oxygen molecules is removed from the water. This separates the Indigo blue into Indigo white in the vat, allowing the Indigo to attach to the fibre. When the fibre is lifted back into the air, the Oxygen returns to the Indigo, and the colour changes from white, to green, to blue.
The fermentation of the vat occurs slowly over several days or weeks. As the vat ferments, the indigo is converted to a dye that will adhere to the fibre.

Indigo Dye
Indigo Dye

Indigo, Fructose, Calcium Oxide
I am using an Indigo – Fructose – Calcium Oxide vat adapted from a dye recipe by J.N. Liles. This vat uses Pickling Lime – Calcium Oxide CaO – (not Calcium Dioxide CaO2) as the alkali.
20 grams of Indigo should dye about 2 kilos of yarn depending on the strength and darkness of colour that you wish to achieve.
1 Indigo Dye: 20 grams Indigo
2 Alkali: 40 grams Calcium Oxide
3 Fermentation sugar: 60 grams Fructose

I make a stock solution of Indigo and the Fructose in small glass jars filled with about 150 ml (6 oz) of water.
This helps to dissolve all of the ingredients before they are added to the dye vat.

Before you start to work with the dye chemicals, put on protective rubber gloves and wear a face mask. Some of the chemicals can be corrosive and the fine dust powders can damage your lungs if breathed in.

Indigo Paste
I have dissolved the Indigo cake into a dye paste before I add it to the dye vat.
Instructions for making the Indigo paste are given in the previous article.
Indigo Dye Cakes

Fructose Solution
60 grams of Fructose + 150 ml of water. Add the Fructose sugar into a small glass jar filled with 150 ml (6 oz) of warm tap water.

Indigo Fructose Solutions
Indigo Fructose Solutions

Because I am using a glass beaker (2 Litre – 3 Litre) as my dye vat, if I were to put all of this dye stock solution into the vat at the same time, this would create a very strong dyebath.
So I only add a portion of the Indigo stock solution at a time – about 1/4 – 1/3 of the stock mixtures. As I dye the yarns and the colour in the vat reduces, I will add more of the stock solutions to the Vat.

The dye vat should be at a temperature of 30-60 deg C (80-140 degrees F) degrees to allow fermentation to take place. Add hot tap water to the beaker and place it into the slow cooker. Fill the slow cooker with warm water as well, and set the temperature to the Low setting to keep the Vat warm. (You can use cold water as well, but it is faster to use the warm tap water.)

Add about 1/4 to 1/3 of the Indigo Paste to the Vat and Stir.
Add a similar amount of the Fructose solution to the Vat.

Add the Alkali
The Alkali changes the pH of the dye solution to a base. For wool dyes this should be between 8-10 pH. Slowly add some of the powdered Calcium Oxide to the dye vat and stir thoroughly. Test with pH strips and continue to add the Alkali to the vat until the pH changes to 8-10.
As you add the Calcium oxide this produces bubbles as the chemicals react with the water.
(CAUTION: Wear your face mask and rubber gloves)

Once the solutions have been added. Stir gently and then wait until a blue flower rises to the surface and the vat has turned a light green or yellow colour. If it is still dark or blue, there is still unreduced Indigo floating in the vat. The unreduced Indigo should float to the surface of the vat and produce a ‘flower’. Wait patiently and allow the chemical reactions to occur.

This can take a few hours for the blue flower to start to form. If it is taking longer, then there may be too much alkali or too much fructose in the vat.

Indigo Flower
Indigo Flower

Testing the Vat
You can test the vat solution by dipping 2 small glass dishes into the vat. Add a bit of fructose to one of the dishes and add a bit of the Calcium Oxide to the other dish. One of them should turn a yellow-green colour. Add a small yarn sample to see if it changes colour to blue.

If the addition of fructose turns the liquid yellow/green then add a bit more fructose to the vat.
If the addition of the Calcium Oxide (alkali turns the liquid yellow/green then add more of this to the dye vat.
Pour the test liquids back into the dye vat.
Give the vat a gentle stir and wait again for the blue indigo to separate and float to the top of the vat, and for the vat to turn yellow/green.

Indigo Vat Test
Indigo Vat Test

Test the pH
When using Calcium oxide I find that the pH can quickly change to 11-12. This is generally considered to be too high a pH for wool yarns. The yarn can be weakened. When dyeing cotton or linen yarns they can withstand the higher pH levels.
The pH can be reduces by adding a bit of vinegar or citric acid to the bath. Check the pH and when it lowers, dyeing can resume.

Neutralize pH After Dyeing
I also have a bucket filled with cool tap water and vinegar. The pH of this should be between 3 and 4. After the yarns have been dyed and oxidized in the air to blue, place the dyed yarn into the vinegar bucket. This will help to balance the pH of the yarns to neutral so that the high alkalinity doesn’t remain in the yarns.

Re-usable Indigo Vat
When you have finished dyeing, DO NOT DISCARD THE VAT.
Indigo vats can be stored and revived for use later. I have had many vats that I have kept going for several months or years. There will be some Indigo dye and other chemicals left in the vat. It is a waste and can be an environmental hazard to pour the vats down the toilet.
Pour the contents into a large glass jar or good quality plastic bucket with a lid and store safely.

Dyeing the Yarns
Indigo Fructose Henna Vat
Indigo Dye Cakes

Indigo Fructose Dye Vat

Safety of Auxiliary Chemicals for Indigo

Indigo dyes and dye kits will soon be available for purchase in my Paivatar Yarn on Etsy and Ebay shops.

Indigo Dye Supplies – Amazon
Crock Pot Slow Cooker – US

Fructose – US

Henna Dye Powder – US

2 Litre Glass Beaker – US

J.N.Liles – The Art and Craft of Natural Dyeing: Traditional Recipes for Modern Use- US
Ethel M. Mairet; Vegetable Dyes- A book of Recipes and Information Useful to the Dyer – US

Last Updated on June 1, 2021 by Paivi Suomi