The leaves of the woad plant in its first-year yield a beautiful blue and I offer a comprehensive guide on my website HOW TO DYE WITH WOAD.
More recently I have been asked how to make a woad pigment from the leaves – so here is the procedure I use very successfully.
Harvest leaves from about April – October.
Put a lid on the container and allow it to steep until the water has cooled and turned dark brown. I usually leave it overnight.
The following day remove the leaves which can be composted and strain through a muslin cloth draped over a colander
You now need to make the solution alkaline by adding ammonia or soda ash to give it a pH reading of 9 or 10 and then oxidizing it.
To oxidize the solution you could use an electric whisk that you no longer use in the kitchen – I use an aquarium pump for between 15 and 20 minutes. Blue particles will now appear on the surface indicating the solution now contains indigo blue.
Once oxidized the solution is ready to settle. After a few hours, the sediment settles at the bottom of the container leaving murky water above it.
Leaving the sediment undisturbed as far as possible scoop out the murky water – I use a hose placed just above the sediment level – clamping it to the side of the container to keep it stable to drain off this water.
When most of the water has been drained fill the container up with fresh water and allow the sediment to settle again – drain again. The water will be less murky but again top up with fresh water and repeat the process until the water above the sediment is clear. You will then be left with a lovely blue sludge. This is your pigment.
Strain through a muslin cloth and allow to drain for a few hours
Or filter through coffee filters/muslin cloths to drain any remaining liquid.
You are then left with a lovely thick paste. Spread it out thinly. Allow this to dry. in a warm place.