Following last week’s post about eco printing with woad, I am back to tell you about my experiment extracting woad dye from second year growth leaves. The dye chemical extracted from woad is an indicant; a precursor to indigo. I followed the steps outlined by Teresinha Robert.
You will need the following: large stainless pot; bucket; thermometer; rubber gloves; secateurs (curved pruning shears) to harvest leaves; pH test strips; soda ash; ice cubes for cooling water; colander for straining liquid; glass jars with lids; electric hand whisk, turkey baster, non stick baking tray; a piece of Habotai silk (large enough to cover the baking tray).
DIRECTIONS: Inspired and adapted from Woad Extraction,” by Teresinha Robert.
Step 1-2: Harvest leaves closely to the base of the plant. I have harvested a 3-gallon bucket of leaves. The leaves are rinsed, and chopped into large pieces.
Step 3: Fill the pot up to two-thirds full with rainwater or distilled water. Put on stove and cook water on medium heat until temperature reaches 194°F (90°C) . Reduce heat to bring temperature down to 176°F (80°C). Remove pot from heat and add the leaves into the pot. Allow leaves to soak and steep in water for 10 minutes.
Step 4: While leaves are steeping in the pot, fill the sink with icy cold water. Put the pot in icy water to cool the temperature. According to Jenny Balfour-Paul, the liquid must cool down quickly, in order to prevent the woad from breaking down. Keep stirring the liquid to help bring the temperature down to 131°F.
Step 5: When the liquid reaches 131°F, place a colander or a sieve over a bucket. Pour the liquid and the cooked leaves into the colander and catch the liquid in the bucket. The soggy leaves are still quite warm to the touch, so put on rubber gloves and press hard on the leaves to extract most of the liquid. Pour the collected liquid back into the pot. The spent leaves are safe for the compost pile.
Step 6: Fill a glass jar with a cup of very warm water and add 3 teaspoons of soda ash. Stir well until soda ash is dissolved. When the woad extraction liquid cools to 122°F , stir in the soda ash (temperature is critical, if the liquid is to hot it can destroy the blue pigment). You will notice the liquid turns to a greenish-brown color almost immediately; at this point your pH test strip should be 9, when dipped into the liquid.
Step 7: The greenish-brown liquid is now ready to be aerated to precipitate the pigment. To do this, I whisked the liquid on high for about 15 minutes with an electric whisk until the froth turned blue, and then to green again. Let the liquid sit for about an hour or so, then gently spoon the froth from the top and discard. The solution in the pot is dark green in color.
Step 8: The liquid should be left undisturbed for a few hours, to allow the pigment out of the solution. Gently siphon (with the turkey baster) the top third of the liquid and discard. Pour the remaining liquid into glass jars. Cover the jars and place in the shade or cool place to let the sediment settle to the bottom of the glass jar (this can take 12-24 hours).
Gently siphon, or pour off the top clear layer of liquid until it is within an inch or two of the layer with sediment. Be careful not disturb the sediment layer too much. You can also use a turkey baster to siphon from the top of the jar. Do the same with the rest of the jars, then consolidate the contents from each jar into one.
Step 9: After a few hours, you will see blue sediment settling at the bottom of the jar. Again, siphon or pour off most of the top layer of liquid away. Then fill the jar with clean water. Set the jar aside, undisturbed, to allow the sediment to settle out again. Repeat this procedure a few more times until the water above the blue sediment layer is clear enough to see.
Step 10: Carefully, pour the rest of the clear water away, leaving the blue sediment at the bottom of the jar. Place a piece of wet silk over the non-stick baking tray. Pour the contents inside the jar on to the lined tray. Leave this out in a warm place to dry, undisturbed. After a day, the pigment dries up and you can gently scrap the blue pigment into a glass container for storage.
I am excited and pleased with the results. The yield from this experiment was 4 grams of dry indigo powder extracted from woad. The next step is to convert the dry powder into liquid vat dye. More on that next time.
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