Fructose Indigo Vat
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Fructose Indigo Vat

Sugar Fermentation Indigo vat

A. What you will need for the fructose vat

  • 20 grams indigo
  • 40 grams slaked lime (calcium hydroxide)
  • 60 grams fructose now + 20 grams later
  • warm water
  • small pyrex jug (1/2 litre)
  • large saucepan, about 8 litres (a narrow and tall saucepan is better)
  • small saucepan or container, about 3.5 litres

You need to use fructose as ordinary table sugar (sucrose) does not work with this vat.

Make sure the slaked lime is fresh, as old lime turns to chalk and does not work.

B. Prepare the indigo stock

1. Prepare the indigo paste with 20 grams indigo and 80 ml water in a small pyrex jug. You will find information on how to prepare the indigo paste here .

2. Add 1 litre of nearly boiling water to your large saucepan.

3. Dissolve the 60 grams of fructose in the hot water in the saucepan.

4. Add 800 ml of warm water to the saucepan. You want the temperature of the liquid in the saucepan to be between 45°C and 50°C.

5. Add the indigo paste to the saucepan.

6. Add 100 ml of cold water to the small jug that had the indigo paste and carefully add the 40 grams of lime. Do not pour water to the lime. Mix well and then gently lower it into the saucepan. Stir well.

7. Check the pH which should be about 11 and at least 10. If it is lower than that, adjust the pH by adding more lime.

8. Cover the vat with a lid and keep the saucepan in a sink with hot tap water as the indigo reduces better with warmth. The solution will become greenish.

9. Stir the vat two more times in the next hour.

C. Prepare the indigo vat

1. After an hour has passed, put 3 litres of hot water in your smaller saucepan, add 20 grams of fructose and stir well.

2. Check that the temperature is between 45°C and 50°C.

3. You now need to transfer the water and the fructose to the large saucepan without pouring!

Fill a small jug with the fructose solution and very gently lower the jug into the large saucepan. Tilt the jug until some of the indigo solution flows into the vat. Then tilt the partially submerged jug to empty it.

4. Check the pH and if it is too low adjust by adding more lime. Stir well and leave for 30 minutes to an hour.

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D. Check that vat is ready

1. Dip a transparent plastic pot in the vat and check the colour by looking sideways at the pot. The colour should be amber or yellowy green.

2. Check the pH again, which should be between 10 and 11.

E. Dyeing with the fructose vat

1. There is sediment in the bottom third of the vat which you must not disturb when dyeing. If you disturb the sediment the vat will go green and you will have to wait for the sediment to settle again. Check in our indigo tips for suggestions on how to deal with the sediment.

2. Warm your cotton or linen fibres in water at a similar temperature to the indigo vat. Wearing rubber gloves, squeeze the fibre while still in the soak water and, keeping it squeezed, lower the fibre into the dye vat and leave for 15 to 20 minutes. Keep moving the fibre inside the indigo vat. Avoid touching the sludge in the bottom.

3. Remove the fibre which will be yellowish green at this stage. Squeeze the fibre, catching the drips in a bucket. Expose the fibre to the air and watch as it will slowly turns from yellow to blue. Let the fibre oxidise in the air for an hour and then rinse it.

4. After dyeing some of your fibre, let the sediment in the vat settle down and dip your plastic pot again. If the colour is still amber or yellowy green, carry on dyeing. If it is dark green, it means that there is too much unreduced indigo in the vat. Judging the colour of the vat can be tricky and you will get better at it with experience. Check the pH, and if it is low add some lime. If the pH is correct, add 2 teaspoons of fructose, stir very well, and leave the vat for 30 minutes to an hour. Check the colour of the vat again. If it has gone back to amber/yellowy green, carry on dyeing otherwise repeat the procedure.

5. If you are getting grey blues, your pH is probably too high.

6. If you want darker shades of blue, dip the fibre back into the indigo vat again. Leave for five minutes and expose to the air for at least 30 minutes. You can repeat this procedure several times.

7. Rinse well following the instructions on indigo aftercare.

8. At the end of the dyeing session, return the contents of the drip bucket to the vat and keep the vat covered.

9. When you want to use it again, warm it up, adjust the pH and add some fructose. If the vat is exhausted, add a new stock solution.

F. Disposal of the fructose vat

Let the vat cool down and add vinegar to bring the pH down to pH 7. Dispose of the vat down the drain.

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Updated on 16 June 2021
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