This Instructable will show you how to extract and use blue dye from a plant that is considered an invasive weed in many parts of the US.
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Step 1: Harvest the Plant
The plant you are looking for is called Woad, Isatis Tinctoria. It is related to broccoli. It forms rosettes in the first year, and yellow-flowered stalks in the second year. Leaves are round at the base, and get more pointed up toward the top of the stalk. Remove the leaves. If harvesting the first-year rosettes, cut them at the base of the plant. If harvesting from second-year plants, cut the stalk at the base, wrap fingers around top of the stalk, and strip the leaves in one quick motion from top to bottom. Rinse the leaves thoroughly. Use leaves within 24hrs or so. Store in a plastic grocery bag if waiting.
Step 2: Process the Plant
Chop the leaves or tear them by hand, but not too small. Heat roughly two gallons of soft water in a stainless steel pot to about 190 degrees farenheit, NOT boiling. Put leaves into the water, cut the heat, and allow leaves to steep for 10 minutes, stirring gently to make sure all the leaves are covered. After ten minutes, cool the liquid further, quickly, using an ice bath or some other method so you can put your hands in the liquid. Using gloves, or bare hands, to wring the leaves as you remove them to get as much liquid out as you can. Remove the rest of the debris out of the water using a colander or cheesecloth so you basically have clear Woad tea. It should be dark yellow-green.
Step 3: Extract the Dye
The dye isn't exactly directly extracted, rather, precursors are extracted in the last step, then put through chemical reactions to form the dye. This involves turning the tea into a basic (alkaline) solution, and oxygenating this to precipitate the insoluble dye.
Take a mug of very hot water and add about 3 teaspoons of washing soda or soda ash and stir in to dissolve. Add this soda solution to the freshly-made Woad tea and stir in. The tea will become dark. Then, take an electric whisk and whisk and stir for ten minutes to get it very oxygenated. Foam will form, and will be shades of green, then blue, then green again. After ten minutes it will likely have blue and green in various shades throughout. Allow to sit for a few hours until foam dissipates.
At this point, the tea will be dark, but the actual dye will have settled at the bottom.
Step 4: Concentrate the Dye
Very carefully draw of the top 2/3 of the tea, stir the remaining amount, then pour into multiple jars. I used canning jars. Allow tea to sit and the dye to settle again for a few hours. You will notice a bright blue line of sediment at the bottom of the jars. Repeatedly draw off the top 3/4 of the liquid in the jars, refill with clean water and let sit a couple hours, until you have deep blue sediment at the bottom and clean and clear water in the jar. At this point, you have your dye and can either dry it by pouring in a ceramic pan and allow water to evaporate then collecting blue powder, or by freezing the dye and water.
I'll update in a little while when I try out dying clothing using an ancient fermented urine vat.