A) Oxidising the Indigo
- Take the fibres out of the vat, wring cotton hard (squeeze wool gently) catching the drips in a spare bucket. Keep the drips till the end of the dyeing session. (In Japan they also beat strong cotton and linen against a hard surface to help remove unattached indigo.)
- Some dyers like to give the fibres a quick rinse by plunging them in a bucket of water and swishing them around for about a minute.
- When you take the fibres from the vat they will be yellowy green and they will gradually change to green and finally to blue. Ideally the complete change of colour should take 30 to 60 seconds (some thicker fabrics may take longer). If the fibres change colour faster than that, there is not enough reducing agent in the vat and you need to add some more fruit sugar, zinc or dithionite depending on the recipe. On the other hand, if the colour change is very slow, the vat is over-reduced; wait about an hour and try again.
- Skeins, particularly skeins of fine yarns, take much longer than fabrics to oxidise and you may need to keep opening the skeins up both when they are in the vat and when they are oxidizing to make sure the indigo reaches inside the skeins.
- Air for at least 30 minutes and always air out of the sun. Keep turning the fibres over as they air, and avoid using clothes pegs which can leave marks on the fabric. Fine yarn needs to be opened up to allow the air to reach the inside of the skein.
- At the end of the day, return the drips that you have collected to the indigo vat.
B) Dark Blues from Indigo
- To get a dark blue with indigo you need to build up several layers by doing multiple dips in the vat and letting the fibre air between dips. Therefore dip, air, rinse, dip, air, rinse, etc.
- The first dip is the longest and you can leave cotton for about 20 minutes and wool for 10 minutes.
- The subsequent dips need to be much shorter, otherwise the vat removes as much indigo from the fibres as it deposits. The zinc-lime vat and the iron vat are both good for building dark blues.
C) Indigo Colour Fastness
- For light and wash-fast colours you need to build up several layers of indigo.
- If you want pale blues, it is best to do several dips in a weak indigo vat, rather than a short dip in a strong vat.
D) Sediment in the Indigo Vat
If you are using a vat that forms a sediment (zinc-lime, iron and fermentation vats), your fabric or yarn must not touch the sediment on the bottom of the vat container. You need to invent a device that will keep the fibre away from the sediment whilst you are dyeing. However, the device must also be easy to remove for stirring the vat every day, which can be messy. Here are a few ideas:
- Drape a net (e.g. garden net used to protect crops from birds) in the vat. You could hold the net in place using clothes pegs.
- Another alternative is to just hold the fabric 6 cm below the surface and keep moving it. This does not work so well if you are dyeing shibori, as you need two hands to open up the folds of the up.
- If you are dyeing skeins, twist the skein once, so it forms a figure of ‘8’. Fold one side over the other making a circle. Put your hands inside the circle. Hold the skein like that inside the vat.
- I have tied the plastic basket of a salad spinner to a metal cutlery basket (drainer). The weight of the cutlery basket keeps this structure upright in the bottom of the vat. Other plastic baskets (clothes, bin) as well as the metal baskets of chip pans may work too. Just make sure they are not used for food again.
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E) Water for your Indigo Vat
If you can, try to use rain water for the indigo vat, if you can’t, tap water is usually OK.
F) Dry or wet fabric in the Vat
Putting dry cotton fabric in the vat may produce a darker and more even colour, as water can act as a resist resulting in a somewhat mottled fabric. However, dry fabric will introduce more oxygen in the vat, and you will need to add reducing agent sooner. Dry fabric also reduces the temperature of the vat. If you want to keep the vat going for longer, soak your fabric in warm water for an hour before putting it in the vat.
G) Greens from Indigo
If you want to get greens you need to over-dye indigo with a yellow dye. You will get a more even colour if you dye un-mordanted fibre in the indigo vat, then use the mordant, and finally dye with the yellow dye. You need light to medium blues for greens, otherwise the blue will overpower the yellow. You can also add fibres that have been already dyed in the indigo vat. However, some of the colour may leach into the vat, and the next item you dye might not be pure blue.
H) Coloured wool for Dyeing
If you are dyeing wool, especially if you are a spinner, you don’t need to start with a white wool. Grey wool dyed with indigo produces stunning slate shades. You will also get darker colours if you start with a grey rather than with white wool. Shetland and Jacobs wool are examples of grey wools.
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