The amounts below will be enough to get the vat started. However, you will need more soda ash, ground madder and bran to feed the vat as time passes.
- You must use ground madder roots as the fermentation does not work with madder extract.
- If you have chopped madder, soak it in water for a day, then use a blender to liquidise it in batches.
This is very important, do not omit this step!
Do a trial run by filling your bucket just with warm water (about 40°C) and placing it over the heating mat. Surround the bucket with bubble wrap and cover it with a towel. Leave it for a couple of days and measure the temperature from time to time. You have to be able to maintain a temperature of between 35°C and 43°C. You also need to avoid sudden changes in temperature. If your vat is kept in the sun in hot weather, the temperature may become too high and the vat will not work.
If your vat temperature is lower than 35°C the fermentation is unlikely to work. You can try one or more of the following, and then do another trial run.
- use a smaller bucket with less water
- add more insulation around the bucket (I found a towel better than bubble wrap)
- use a larger heating mat
- use both a heating mat and a beer-making heating belt
- place hot water bottles over the vat
- make the vat in warmer weather
- some dyers use a fish tank heater inside the vat, however, I am not happy with leaving an electric cable inside an alkaline environment.
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1.Simmer the ground madder and the bran in two litres of water for 30 minutes.
2.Place your 50 x 50 cm piece of silk chiffon over the plastic sieve. Rest the sieve over the saucepan. Carefully strain the liquid. Let the liquid cool to 40°C and add the liquid to the bucket. Don’t throw away the madder and bran, keep it to one side as you will use it again.
3. Place your bucket on the heating mat and add about 6 litres of warm water (40°C). Make sure you leave about 4 cm of air space at the top. The least air space you leave the better. However, it is important not to fill the vat to the very top; otherwise it will overflow when you add the fibre.
4. Add 15 grams of soda ash to the bucket. Stir well to dissolve. Check the pH, if it is below pH 9, add a little more soda ash.
5. Spoon the indigo onto the cotton handkerchief and make a loose bundle. Tie the bundle with a string and suspend it in the vat.
6. Cover the bucket with a lid and drape a towel over the bucket, keeping it clear of the heating mat.
7. Switch the heating mat on.
8. Wearing rubber gloves, rub the bag of indigo once a day to release a small amount of the fine indigo. Instead of rubbing the bag, you can poke it gently with a stick. Condensation will have gathered on the lid, so open the lid carefully and make sure the condensation does not drip back into the vat. Let the condensation drip into a separate container.
9. It is very important to check the pH everyday for the first five days, then from time to time. The fermentation creates lactic acid which lowers the pH and you will find that the pH tends to drop as low as 7. When this happens add one teaspoon of soda ash to the vat, stir gently and measure the pH again. The pH should be about 9.
10. Simmer the reserved madder and bran again, strain and add a bit of the liquid to the bucket in 2 or 3 days if there is space. Keep this liquid to feed the vat later when it needs it. Make sure it is clearly labelled and you might need to be refrigerated.
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The vat will usually be ready in five days, but it can take as long as two weeks. The vat is ready for dyeing when it develops a bronze sheen on top. The fermentation vat does not go yellowy green like the chemical vat, it is more a deep bottle green. If you are not sure, check by dyeing a small strip of cotton fabric.
Warm the fibre in water at a similar temperature to the indigo vat for a couple of hours. Wearing rubber gloves, squeeze the fibre while still in the soak water and keep it squeezed as you lower the fibre into the dye vat. Release the fibre. If it is wool, leave it for 10 minutes. If it is cotton, you can leave it in the vat for a couple of hours or overnight. Remove the fibre and expose to the air for an hour. Rinse. To get a dark blue repeat this procedure several times.
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Between dyeing sessions the vat must rest overnight or an extra day. The vat will need regular feeding. To feed the vat, simmer 2 or 3 teaspoons of madder and half that amount of bran in half a litre of water for 30 minutes, then strain it and add the liquid to the vat. Whenever the dye weakens, you can renew it by rubbing the bag with indigo, or adding more indigo and the other ingredients in proportion. The vat will take four to five days to get ready again. This type of vat can last for a long time and some indigo vats are over 100 years old.
-Adding the simmered madder and bran to the vat without straining it first will help the fermentation. You will need to stir the vat gently twice a day to integrate the ingredients that settled to the bottom, back into the solution. As there is now a residue in the bottom, don’t stir the vat on the day you are going to use it to avoid disturbing the residue. Place something in the bottom to keep the wool away from residue. Add more madder and bran in 2 to 3 days.
[If the sediment causes a problem, you can make a silk chiffon bag to hold the madder and bran and still allow them to move about freely and react with the other ingredients on the vat.]
-If the vat has developed mould at the top, it means that it has become too acid. Remove the mould and add some soda ash.
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Updated on 28 November 2020
Website & photos by Mike Roberts ©2006-20 Wild Colours natural dyes