1. Harvesting the woad leaves
July and August are the best months for harvesting woad in the UK. Cut leaves from first year woad plants with secateurs, near to their base, and fill a supermarket carrier bag full (about 1250 grams).
Wash them well under the tap. Wash again by dipping and shaking a handful at a time in a bucket full of water. There is almost no blue dye in the stalks and, therefore, you can remove the stalks if you have many leaves.
2. Woad production - Tearing the leaves
Tear the leaves by hand (much easier than chopping them with a knife), and do not tear them too small otherwise they will go through the colander later on. It is OK to pick woad leaves either in late morning or in mid afternoon and then process it early the following morning.
If you can't process the woad straight away, keep the leaves in a closed supermarket carrier bag in the shade but not in the fridge.
3. Dye Extraction - Steeping the leaves
Fill a 10 litre stainless steel saucepan two-thirds full with water. It is best to use soft water, e.g. rain water. Heat the water up to 90°C but do not let it boil inside the saucepan.
Put the leaves in the saucepan and let them steep for just 10 minutes in water at 80°C.
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4. Cooling the liquid
Remove the saucepan from the heat and put it in a bowl full of cold or icy water. According to Jenny Balfour-Paul, the liquid must cool down quickly. This appears to be to prevent the woad from breaking down.
I aim to get the liquid down to 55 degrees C in 5 minutes. I keep stirring the saucepan and changing the water from the bowl. Sometimes I put a tray of ice cubes in the bowl to cool it more quickly.
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5. Straining the liquid
When the liquid has reached 55 degrees C, put a colander over a bucket and then strain the liquid through the colander.
Put on rubber gloves to press the leaves and extract all the liquid. Pour the liquid back into the saucepan leaving the debris behind in the bucket. The spent leaves can then go on the compost.
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6. Adding soda ash
Fill a mug-size container with boiling water and add 3 teaspoons of soda ash (it produces less froth than washing soda), dissolve well and let it cool slightly.
Click to buy soda ash here
When the woad extract liquid in the saucepan has cooled to 50°C, add the soda ash. Do not put soda ash when woad solution is over 50°C, or you will destroy the blue.
The vat will turn to a greeny-brown colour and the pH should be about 9. Buy pH paper here.
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7. Aerating the vat
The woad vat now needs to be aerated to precipitate the pigment. To aerate the vat, whisk with an electric whisk or a manual one. Some people pour the liquid from one saucepan to another.
I usually whisk for 10 minutes with an electric whisk until the froth turns blue and then green again. Sometimes the froth remains blue however long you whisk but this does not usually affect the results. Once, in late September, I had almost no blue in the froth but, to my surprise, a large amount of woad pigment settled out.
It takes about two hours for the froth to subside and I found it better to discard the froth using a spoon. After discarding the froth you will end up with a dark green solution with no hint of blue in it.
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8. Settling out the Woad Pigment
Let the pigment settle undisturbed for 2 to 3 hours. Using a soup ladle, very gently transfer a third of the liquid from the top of the pan into a bucket. Pour the remaining liquid into 4 or 5 large coffee jars with the help of a funnel. Put the jars in the shade and let the sediment settle for a couple of hours.
Gently tip the liquid from the top of each jar into the bucket, leaving the last 6 cm of liquid in each jar. Using a large pipette (for example, a glass siphon sold as a turkey baster in kitchen shops) to siphon liquid from the top of the jar is even better. The pipette allows me to remove most of the unwanted liquid with little disturbance to the pigment in the bottom of the jar. (Pipettes sold in wine making shops are often not very useful, as they are designed to remove pigment from the bottom of a container, rather than skim liquid from the top).
Consolidate the contents of the jars into one jar.
There is a small amount of pigment in the bucket, which could be used to dye a scarf with the chemical dyeing method, but I usually throw the contents of the bucket away.
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9. Concentrating the Pigment
Let the liquid in the jar settle for a couple of hours. You may see a blue sludge at the bottom of the jar. Carefully empty 2/3 of the jar or siphon most of liquid away with a glass siphon. Then fill it again with clean water. Repeat two or three times more until there is clear water over blue sediment. This is very exciting!
[I have tried filtering woad using an old gold-plated coffee filter, but the woad went straight through. I have also tried a car pollen filter, supposed to be 100 micron, but the pigment went straight through that as well. The woad pigment does not go through proper filter paper used in chemistry. I put a square of filter paper folded inside a funnel, and the liquid dripped very slowly. It took me 24 hours to pass all the liquid through the funnel].
We are currently using a piece of Habotai silk to filter the woad pigment. First wet the silk, then place it on the funnel, with plenty of silk overhanging the borders of the funnel. Slowly pour the liquid into the funnel. A very small amount of pigment may go through, but most of the pigment stays on the silk. You let the pigment dry on the silk and gently scrape it away with a blunt knife.
In the past we used Whatman Grade 1 filter paper, which has an 11 micron retention size, but a slightly larger micron size might also work well.
Fill the jar to overflowing one last time, and put lid on tightly. The woad should last for a year or more. It is better to use a glass jar to decant and store the woad pigment. In the past, I have used plastic soda water bottles and the woad pigment stuck permanently to the walls of the bottle.
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10. Making woad dye - Drying the Pigment
The woad can now be used for dyeing or dried for more permanent storage. To dry the woad pigment, pour or siphon away as much water as possible from the glass jar, and then empty content of the jar into an old Teflon saucepan or frying pan; an old ceramic plate can also be used.
After a few days the woad dries up and peels easily from the saucepan. It helps if you keep the saucepan somewhere warm, such as near a radiator. I have tried drying on greaseproof paper, but the pigment stuck to the paper.
One large woad plant weighs about 700 grams. 1 kilo of leaves will produce between 1 gram to 4 grams of pigment. The yield depends on the soil, how well the plants were fed, and how warm the summer was. 1 gram of woad will dye about 20 grams of fibre. So if you only get a very pale blue from your first experiment don’t despair. Try feeding your plants more, and collecting the pigment from several extractions, to get darker colours.
Teresinha at Woad.org.uk
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Last updated on 28 November 2020
Website & photos - Mike Roberts © 2006-20 woad.org.uk