I've been doing a bit of woad dyeing this last week and have been particularly pleased with the results. In this instance I started with woad powder as I have no woad in the garden currently, but otherwise the method is much the same as if you were starting with woad 'tea'.
Two loads of yarn later, here's the results. The yarn on the left is a naturally very pale grey which came out beautifully slate blue with the woad, and on the right the larger skein was a natural creamy white wool that has taken the colour very evenly and is a glorious glowing blue.
I couldn't resist knitting some up right away, the two Monmouth 'labourer's caps' here are in the natural pale grey and the slatey blue, and have been through a hot wash to full them, which is always a good way to check that your dye is stable on the fibre :)