EXTRACTING WOAD DYE
Harvest about 1.2 kg woad leaves and wash. Roughly tear into pieces. Fill a 10-litre stainless steel saucepan two-thirds with water, heat to 90°C then turn off heat. Add leaves, place the lid on top and steep for 10 minutes. Place the saucepan in a sink of icy water to cool rapidly. When 55°C, strain into a bucket. When you are sure the temperature has dropped to 50°C, add 3 teaspoons soda ash. Stir to dissolve. Measure the PH – it should be about 9. If below 9 add more soda ash. Aerate the liquid with a whisk for 10 minutes, when a froth will appear. Let the dye sit for 2-3 hours, during which time the foam will evaporate and any pigment will settle. Scoop or siphon off (with a pipette) all the water, leaving the pigment at the bottom. Fill with water again and repeat 2 or 3 times. Soon you will have clear water at the top and thick pigment in the bottom. This is your woad dye.
No two batches of plant dyes will be identical in colour and strength.