The Plant EditWoad is a biennial plant which produces blue dy. The first year broad, large leaves are used for dye. The plant produces a large taproot and the larger the root, the more dye is produced. Woad was one of the earliest dyes used in Britain, where it was also reported to have been used as a body paint. 
How to Harvest Edit
First year leaves can be harvested up anywhere from 2-4 times.  Woad is considered a noxious weed in some areas, and can usually be harvested heavily in the spring. It tends to spring back and can be harvested again in the summer and fall, before the first frost. Because it is a difficult plant to get rid of, it can be harvested heavily. 
How to Extract Color EditWoad dye should be processed immediately from fresh leaves. Leaves lose dye potential the longer you wait between harvest and processing. Once it has been fully processed, it becomes stable and can be stored for later use. 
A traditional preparation began by pulverizing the leaves, adding water, and fermenting the leaves until they formed a dark substance which was then used to dye. 
Contemporary dyers begin by tearing the leaves and placing them in a pan with soft water or rain water. The leaves are heated to 90°C for 10 minutes. The pot must be cooled quickly to prevent the dye from breaking down. This can be done by half submerging the pot in an ice bath. Once the dye bath reaches 55°C, the leaves are strained out and the liquid pressed out to ensure the most dye is extracted. Once the dye pot is below 50°C, soda ash is added. If soda ash is added when the pot is too hot, it will destroy the blue. The pot will turn green-brown and the pH should be around 9 at this point. Next, whisk the dye pot for 10 minutes to aerate. The woad is then left to settle. The dye pigment will sink to the bottom and the water can be slowly poured off, leaving a concentrated dye. The final step is to allow the water to evaporate from the pigment. Dried pigment can then be stored for later use. 
Once the leaves have been strained from the dye bath and squeezed well to extract as much blue dye as possible, they can then be simmered in water and used for a second dye with alum which produces "woad pink".
- ↑ 1.0 1.1 1.2 Grierson, S. (1986). The colour cauldron. Perth: S. Grierson.
- ↑ 2.0 2.1 How to Store Woad Pigment for later use. (n.d.). Retrieved July 21, 2015, from http://www.wearingwoad.com/how-to-store-woad-indigo-pigment-for-later-use/
- ↑ Tersinha, R. (n.d.). How to Extract Woad Dye in 10 easy stages. Retrieved July 21, 2015.