The Journal for Weavers Spinners and Dyers

Woad from seed to dye

Carolyn Griffiths, Frome and Online Guilds

There is currently a strong interest and a resurgence in using natural dyes, but natural does not equate with safe, or necessarily environmentally friendly and sustainable. In Tudor times woad, Isatis tinctoria, was grown in this country to the exclusion of food as the crop was so profitable. Laws were eventually enacted to license and restrict its planting. It was also forbidden to be processed within 15 miles of the palaces of Queen Elizabeth I,
and five miles from a market town, because of the pungent smell – so perhaps something to be mindful of when dyeing! I enjoy growing woad in my garden and I have found that the following methods work well for me, as the magic of indigo is so captivating.

Green and black woad seeds
Green and black woad seeds

Woad, a member of the cabbage family, is a standard biennial that produces a rosette of leaves in the first year and flowers in the second year. Most woad seed, if kept indoors at room temperature, typically only lasts a year. Some of the seed will last two years but you cannot guarantee germination on anything older than a year. Ideally the seed needs to be sown outdoors in March in a sunny spot where you want the plants to grow. The plant takes up nitrogen from the soil and grows best in a well-drained loam or clay. It has a deep tap root and does not particularly like to be transplanted. If you already have woad which has flowered it often self-seeds vigorously, but not necessarily where you want it. It is best to collect the seed and then plant it the following spring.

Sowing seed
Sowing seed
Woad tap root
Woad tap root

The seeds can be sown directly in the ground in rows about 5in (12.5cm) apart. The individual plants, when they are about 4in (10cm), will need to be thinned to about 10in (25cm) apart. Once they germinate, they need to be kept clear of competing weeds on a regular basis until the plants become established. Close planting reduces some of the need for weeding. As a precaution, plant twice the number of seeds that you think you need and use your favourite method of control for slugs and snails, as the emerging green shoots are readily enjoyed. This is one of the reasons I start my seeds indoors, even if I lose quite a few when transplanting. I like to recycle plastic containers with perforated bases, three-quarters filled with a mix of seed compost and grit for drainage. Stand the container in a tray of water until it is evenly moist. Sow the seed thinly on the surface and cover with vermiculite and place on a sunny windowsill. Keep the soil damp; I have found that the seeds generally germinate in about ten days. Once they are about 2in tall, I put them in individual pots to grow on, and then harden them off, before transplanting them outside to a permanent site in April.

Harvesting and processing leaves

Woad leaves showing purple tip
Woad leaves showing purple tip

By the end of July, the leaves will be about 10-12in (25-30cm) long, and some of the tips may start to change to a purple colour. This is a good time for the first harvest and making a fresh leaf woad vat. Indigo from woad has the same chemical composition as all other indigo; it is the other chemical compounds in the plant that makes the blue shade vary towards the pinks or the greys. The final colour depends on the nutrients in the soil, the sunshine and the time it is harvested. Woad will dye most natural fibres, although I have not tried it with some of the newer ones made from milk and soya protein. There are lots of different recipes for dyeing with woad leaves; the following is a chemical vat that I have often used, but there are many more in books and online. Unlike Persicaria tinctoria, Japanese indigo, you cannot dry the woad leaves for using later; this is why historically the ‘waddies’ made woad balls which concentrated the indigo precursors in a series of fermentation processes.

On a dry day, preferably following a few sunny ones, collect 200% fresh leaf to weight of fibre. Naturally there is no way of knowing how much indigo your plants will produce, so you may get anything from light to mid-blue, and occasionally dark blue if you are lucky. Put the leaves in a bucket of cool water to remove any dirt that might contaminate the dye extract. While the leaves are soaking, collect your equipment:

Remove the leaves from the water, tear them into small pieces and set aside. Work in a well ventilated area. Bring sufficient water to cover the amount of torn leaf to the boil. Add handfuls of leaves to the boiling water and use the stirrer to submerge them. Put the lid on, turn the heat low and simmer for 30 minutes. Make sure the water does not boil as this will destroy the indigo. The liquid will turn from clear to a deep sherry colour with an oily film on the surface. While waiting, fill a sink or large container with cold water and ice or ice packs; the aim is to cool the liquid as quickly as possible to hand hot as this helps extract the maximum indigo.

Chopped leaves
1. Chopped Leaves, 2. After simmering the leaves turn dark with a film on the surface, 3. Sherry coloured extract

After 30 minutes, place the pot in the cold water to cool; stir both the liquid in the pot and agitate the surrounding water in the sink. Once hand hot, pour through the sieve to remove all the leaf matter and squeeze it. Save all the liquid and discard the leaves on the compost. (They can be simmered a second time as for other dye plants and will yield a fresh plaster-coloured pink on alum mordanted wool, but I have found that it fades quite quickly).

The next step is to make the liquid alkaline; this will change it from sherry-coloured to a dark bottle green. I usually have about 2-3 litres of liquid so I start by adding 1 teaspoon (5ml) of washing soda crystals, stir gently and wait a few minutes, then check the pH which should be between 9 and 10, and the colour should change. (As the liquid is quite dark, it may colour the pH paper; insert just the very tip of the paper and let the liquid travel upwards, then read the value above any discolouration). If necessary I may add a little more washing soda. An easy way to see the colour is to insert a white plastic spoon. This stage complete, the liquid needs to be oxygenated. There are several ways to introduce oxygen, by either pouring the liquid from one pot to another or using a whisk. This will need to be done for about ten minutes.

Blue froth will gradually form on the surface as the insoluble indigo pigment is formed from the plant's chemical compounds of indican and isatin B. It is now time to reduce the solution so that the indigo can dissolve and bond with the fibre. Put the pot on the stove and raise the temperature to 50°C, place it on a hard surface and sprinkle about 10g of sodium dithionite on the liquid (froth) and give it a very gentle stir. Put the lid on and wrap the pot in bubble wrap and towels to keep it at a constant warm temperature. I tend to leave it overnight at the same time as I am wetting out the scoured fibre.

The following morning, by inserting the white plastic spoon, I can check the colour of the solution which should have changed from dark green to clear yellow with a few blue streaks. If this has not occurred, I repeat the process as above (from heating to 50°C) and leave it for another couple of hours.

pouring liquid
1. Oxygenating the alkaline liquid, 2. Froth on the surface will turn blue as indigo exposed to the air will oxygenate, 3. Reduced dye solution

                                                                                                                                                                                                                                                      Having gone to the trouble of removing the oxygen to make the indigo soluble, you need to minimise its reintroduction. I squeeze out my wetted fibre and carefully slide it into the liquid. For the first dip I leave it in for about twenty minutes, and to obtain an even and slightly darker shade each subsequent dip is only a couple of minutes. To remove the fibre, I hold a bowl next to my dye liquid and as I take it out, I quickly place it in the bowl so as not to let it drip back into the solution, as that would introduce oxygen. I then squeeze the excess liquid from the fibre and only add it back to the pot if I am repeating the heating process. After each dip the fibre has to be aired for at least 15 minutes; this is the magical moment when the fibre changes from yellow to green and finally to blue as the indigo reverts back to insoluble pigment. Wool fibres will dye better if the solution is kept at a constant 50°C, but cotton can be dyed at a cooler temperature.  

Shades of blue
Shades of blue dyed wool from woad harvested at different times of the year
Wet silk
Wet silk dyed with woad

Once dyeing is complete the damp fibres can be left overnight in a bucket of cool water to fully oxygenate before washing them the next day with a mild wool soap. Washing removes any excess indigo that has not properly fixed to the fibre, and for the last rinse, I add a tablespoon of vinegar to neutralise any remaining alkalinity from the washing soda as this has a tendency to give the wool a harsh handle. I may reheat the solution a couple of times. When it is exhausted of colour I dispose of it by whisking to add oxygen to neutralise the sodium dithionite, and then adding a couple of tablespoons of vinegar to neutralise the washing soda. I then pour the liquid in a waste area of the garden.

Note: there are many other methods for extracting indigo; I would recommend any of the books by Jenny Dean. I would also like to extend my thanks to Susan Dye and Ashley Walker for their helpful comments; for lots more information on dye gardens visit their site www.naturesrainbow.co.uk

About the author: Carolyn really enjoys travel and research, in particular eighteenth century English textiles. Author of Woad to This and The Cloth Trade of Frome, and Dye Editor for the Journal.

Editorial note: In some locations, woad is classified as an invasive weed; review local environmental laws. See also Notes on Health and Safety on p.10.

All photos: Carolyn Griffiths

cover

This article appears in edition #273 of the Journal for Weavers, Spinners and Dyers.

The Journal is published on behalf of the Association of Guilds of Spinners Weavers and Dyers. It covers a wide range of textile subjects, including articles on historic textile techniques and cutting edge modern design.

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