One of the fun things about natural dyes is being able to use the natural dye plant to its full extent. Which can often include creating an extra dye vat after your initial dye vat is completed, at least in the case of the woad plant. Being able to get more than one color from this plant is another way that woad is eco-friendly and sustainable.
This is part three of the Woad to a Sustainable Blue. Part one discussed finding a sustainable blue in an unsustainable world. Part two discussed why Woad matters in the hunt for sustainable clothing. In part three, we are discussing some of the more creative dye uses of the woad plant, and the non-blue colors that can be achieved from Woad as well.
No matter how much I study natural dyes, I will probably always think that the woad plant is the most amazing dye plant. Not only does it give blue, and is the only plant in northern climates that will. But it is good for far more colors than just plain blue. Using just the woad plant, you can actually produce a rainbow of colors, including yellow, pink, red, purple, and blues. While red and purple are a little more of a challenge, being a side aspect of the woad vat itself, the yellow and pinks are easy to achieve from the leaves, after the indigo is extracted, and before the leaves become acquainted with the compost pile.
Yellow or Pink from post-extraction leaves:
The color given by woad leaves, post indigo extraction, will either be a yellow or beige color or a pinky beige. In my science fair experiments, the woad plants sourced from England gave the pinky beige and those sourced from North America gave yellow, while those from France gave a slightly darker yellow. Thus your local woad plant may give different shade, and it may well be unpredictable.
To get yellow or pinky beige from your woad leaves, you will be required to perform a standard indigo extraction. Once the extraction is completed, and the leaves are rung out and set aside, it is time to begin. Throw the rung-out leaves into a fresh dye pot and cover with water, bring that to a simmer for around 30 minutes.
After simmering, strain out the leaves and put mordanted wool or silk into the vat. Bring the vat to a simmer again, and let the wool or silk soak in the vat for several hours. The vat only needs to simmer for a few hours, but you can leave the fibers in the cooling vat up to overnight.
Take out the fiber. If it is beige, you can try a rinse with washing soda (or soda ash) to change the pH. With yellows, a rinse of washing soda or soda ash can change blah beige to a nice crisp yellow. If you use a pH shift, always make sure to neutralize your wool or silk afterward as a high pH can damage the fibers.
Once your fibers are completely dry, you will be able to see what after-extraction colors your particular woad plants will produce. The colors from the after-extraction bath usually work exceptionally well in conjunction with the other woad colors, and look awesome if combined together in weaving or knitting. 
After The Extraction Settles:
When your woad indigo extraction vat is completed and has settled, you can draw off the top of the liquid to access the precipitate on the bottom. The precipitate can be dried, or frozen, for later use. However, that leaves one with a large quantity of green-blue liquid that is drawn of the top of the precipitate. What is one to do with that as, with all that color in the water, there is bound to be some dye in it?
Easy answer, reduce it!
The water drawn off the top of your indigo precipitate still contains some indigo molecules. Following normal procedure, warm the water, change the pH to 10, and add your reducing agent. Then, drop in whatever you want to dye and follow the normal vat and re-vat techniques for dyeing with indigo.
At the end of a few vattings, you will probably find that your color is not darkening. This is because there is not a huge amount of indigo suspended in the water. Your fabric, yarn, or fiber may also look green instead of blue. This is normal.
If you want a blue from the non-precipitate extraction liquid, you will need to rinse the fibers in a mild acidic solution to neutralize their basic tendency. This will turn a pure woad green into a blue. However, if you do not neutralize the fibers, the green will remain and is light and wash-fast (provided it is not washed in an acid). At any time, if the woad-green gets something acidic on it, it will become blue, but it will stay green as long as the fibers remain on the basic side of things.
Using Everything for Dye
As the previous section shows, more color is obtainable form the woad plant than just blue. Re-using the leaves provides and extra layer of color, and also breaks down the leaves more so that they will compost quicker.
While the leaves are the main part of the woad plant used for dye, other parts of the woad plant will also produce color. While most people consider that only the first year plants will produce indigo, in actuality the second year woad flowers and stalks will also still produce indigo. The only challenge is that, as the stalks are pithy and hollow, the indigo ends up being less concentrated when compared to the first year leaves.
The roots of the woad plant are usually discarded by dyers, and sometimes used by herbalists. I have not yet tried dyeing with woad roots. However, I am sure you could get something from them since everything above ground has dye, of some kind, in it.
If you have ever tried direct contact dyeing, you will know that it is a fun technique which includes some fermentation. The woad flowers make awesome blue prints in direct contact dye applications. In the experiments that I did, the blue remained permanently on the fabric, even when rinsed with a mild acid or base solution. Since blue is one of the harder colors to exploit in direct contact dyeing, being able to use parts of the woad plant in it, makes it much more colorful and fun.
Direct Contact Dyeing With Seeds
Due to woad being considered an invasive, or aggressive, plant one must always insure that the seeds are controlled. However, if you save seeds every year or even every second year, you will soon find that you have more seed than you could ever plant. However, after the fifth year the seed is no longer viable enough to plant. Which begs the question, what can we do with all this seed?
Enter direct contact dyeing. Woad seeds work amazingly well in direct contact dye applications, even better than the second year stalks and flowers.
After doing a basic direct contact dye scarf or piece of fabric, let it dry and make sure to fix the color. Then, re-soak in water and liberally sprinkle woad seeds on the fabric. Roll it up, and pound it. Then heat it and let the woad seeds have a day or two (or three) to ferment in the fabric.
When the seeds are removed, if the woad seeds fermented right, you will have blue dots everywhere over the fabric, possibly some green dots and purple dots as well depending on what the base colors were. After brushing off the seeds, wait a few minutes to an hour to let the dots oxidize. Frequently, due to the fermentation, the seeds will leave a dot of green that will oxidize to blue once it is exposed to air. Make sure to let the fabric oxidize fully before rinsing, and to rinse in a lightly acidic medium as sometimes woad blue will remain green without a mildly acidic rinse.
As the heating and fermentation kills the seeds, you need have no fear of discarding the used plant matter when your direct contact dyeing is finished.