Preparing an Indigo Dye Vat

Indigo DyesIf you are curious about indigo dyeing this blog post may encourage you to have a go! Here we take you through the stages of preparing the indigo dye vat and dyeing your first items with this magical, ancient dye. Dip you fabric, fibre or yarn, lift it into the air and watch as the luminous green turns to the stunning colour of indigo.

Materials & Tools List for Dyeing with Indigo

  • 25g Indigo Dye Powder
  • 50g Thiourea Dioxide
  • 200g Soda Ash
  • 1 litre mixing dish with lid (or cover with cling firm / plate)
  • 20 litre dye vat (garden tub, plastic bin, brewers bucket etc)
  • Stirring Stick (long enough to reach the bottom of the dye vat)
  • Tongs (or coat hanger, string, mesh bag etc)
  • Rubber gloves
  • Thermometer (optional)
  • Clothes horse or washing line

(The following items are included in the Fibrecrafts Indigo Dye Kits; 25g Indigo, 50g Thiourea Dioxide, 200g Soda Ash, 1 litre plastic jar with lid and 1 polypropylene stirrer.)

Making the Stock Solution for the Indigo Dye Vat

  1. Mix together 25g of indigo dye powder and 15g Thiourea Dioxide in a container (we have used a 5 litre container for this demonstration.
  2. Slowly add 150ml of warm water to make a paste.Paste made from Indigo powder, Thiourea Dioxide and warm water
  3. Cover the paste mixture and leave to stand for 10-20 minutes.
  4. In a separate container, add 150g of Soda Ash (sodium carbonate) to 500ml warm water and stir until dissolved.
  5. Slowly add the Soda Ash solution to the Indigo Dye paste and stir until combined. Replace the cover and allow to stand for 30-60 minutes. If possible try to keep the stock solution around blood heat (36-37°C).

Preparing the Dye Vat to Receive the Indigo Stock Solution

The vat is designed to dissolve the solid indigo and convert it to the soluble form in the liquor; leuco-indigo.

  1. To make the dye vat you will need a 20 litre container half filled with warm water (no hotter than 50°C).
  2. Dissolve ½ teaspoon Thiourea Dioxide and ½ teaspoon of soda ash in a jar of warm water, pour into the dye vat and stir.
  3. Cover for 20 minutes and allow the Thiourea Dioxide and Soda Ash solution to reduce the oxygen in the water.
  4. Gently add about half your stock solution to the vat (keep the remainder to recharge your indigo vat should you need it). Any white precipitate in the stock solution may contain undissolved indigo so avoid disturbing this layer if it has formed (if in doubt, pass the stock solution through a strainer to help prevent unreduced indigo powder from entering the vat).Adding the indigo stock solution to the dye vat
  5. Stir the stock solution into the water very slowly to prevent introducing oxygen into the liquid. Cover the vat for 20-30 minutes before use.Stirring the Indigo Dye Vat

Using the Indigo Dye Vat

To help achieve an even coverage of colour, your fabric, fibre or yarn should be prepared for dyeing. The materials should also be pre-wetted by submerging in water and squeezing out the excess. Natural fibres such as silk, cotton and wool will readily absorb the indigo dye molecule, some synthetic fabrics (such as polyester) may not perform so well.

Our images below show cotton fabric which was been Shibori tied (a Japanese tie-dye technique).

  1. Gently lower the pre-wetted item into the dye vat, taking care not to introduce oxygen into the indigo dye solution.
  2. When the fabric is first put in the liquor it is important to make sure the fabric structure is fully saturated in liquor. That involves working the fabric with your hands.
    Lowering the tied cotton into the Indigo Dye VatShibori dyeing with indigo dyeTo ensure that the dye absorbed fully into Cara’s cotton parcels they needed to be submerged for slightly long than untied fabric. She used a wooden pole with a hook at either end to lower her tied cotton parcels into the indigo dye vat. She hooked the other end of pole over a ruler placed across the top of the vat. String or coat hangers can also be used to suspend items in the dye solution. Use rubber gloved hands or tongs to carefully work the dye into the fibre.
    Indigo dye vat in use
  3. As you remove the fibre from the vat, squeeze it gently to remove surplus liquor.
  4. Hang up to oxidise. The oxygen in the air returns the leuco-indigo to indigo. Give it time to complete the process (10-15 minutes) while the colour changes from yellow-green to blue.
  5. You can increase the depth of colour by repeated immersion in the vat. Put the fabric back into the vat for a short period (15-30 seconds) without agitating it and then expose to the air for at least 15 mins before repeating the immersion. Keep immersing and oxidising until the desired blue is obtained. NOTE: With subsequent dips the liquor attacks the solid indigo and starts to strip it from the fabric. On that basis leave it in the vat for as little time as possible. Take it out and allow to oxidise for as long a time as possible. Repeat the short dips and long airings as many times as you need to get the required depth of blue.Green colour of indigo dye
  6. Hang up to oxidise (for 10-15 minutes) while the colour changes from yellow-green to blue.
  7. Continue immersing and oxidising until the desired depth of indigo blue is obtained.Shibori parcels with oxidised indigo dye
  8. Wash your dyed item in a bowl of water to which two tablespoons of vinegar have been added to neutralise the soda ash. Allow to soak for 20-30 minutes. Rinse well in clean water.Rinsing out the indigo dyed fabric
  9. Hang out to dry!Indigo dyed Shibori on cottonTie dye with Natural Indigo dye

Maintaining your Indigo Vat

The Thiox (Thiourea Dioxide) indigo vat is very easy to maintain.  As all the ingredients are soluble, so a balanced vat is completely clear making it easy to see just what is happening.

The vat can use up all reducing agent.  This can happen during resting (a vat with a good lid will last months) but eventually it will need refreshing.  This need is shown by a deposit of blue indigo at the bottom of the vat, which may look green-ish.  Simply add 20–40g of Thiourea Dioxide and stir, then wait a few hours for the vat to be ready for work.

A vat in use can also use up all the soda ash which reacted with the thiox to reduce the indigo.  When this happens there is a white sediment at the bottom of the vat (it may look yellow-ish).  In this case add 20 – 40g soda ash.  Again stir and wait a few hours.

The last possibility is that you are getting a weak indigo colour in your dyed fabric.  This suggests that you have used almost all the indigo.  Add more, and if it lies at the bottom unchanged, add both thiox and soda ash in the quantities above, stir and wait.

In this way you can keep your vat working for a very long time without any build-up of residue or sludge.

Disposing of an Indigo Vat

The products of dyeing in your vat have much in common with household cleaning agents.  When you need to dispose of the liquor it can be flushed into the town drain system or poured in a patch of waste land without any worries.  The local sewage system is used to far worse.

Visit the Dyeing section of the George Weil website to view Indigo dyes, Indigo Dye Kits, other dyes & dyeing equipment

Copyright © 2019 George Weil & Sons Ltd


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