Woad (Isatis Tinctoria) is easy to grow. Buy some seeds, and watch the plants develop over 2 years. They flower on 3ft - 4ft stems in 2nd year (top image) turning to aubergine chandeliers of seeds. They self seed so long as ground is moist.
[Add link to roses silk painting over blue dyed silk]
Boil then simmer woad leaves for an hour – liquid is sherry coloured.
Add soda crystals at 50 deg. until alkalinity reaches Ph9.
Whisk liquid until froth forms in about 10-15 mins. Liquid can also be poured from one pan to another to airate, make bubbles.
Heat dye bath to 50 deg again. Set aside 20 mins. Add desert spoon sodium dithionite to remove oxygen. Add enough until dye bath turns limey green.
Place silk in liquid carefully without creating air bubbles. Submerge. Leave for 20 mins. It starts to work soon if some fabric is left out in the air (see Process Main Gallery).
Remove fabric and rest it. Watch it turn blue in air. (mine went turquoise on ahimsa cream silk using pond water).
Rinse out when colour as dark as will go, hang out to dry.
Note: I returned my 1st session dyed cloth to the dye bath, which then REVERSED the process (as recipes warn). Best to leave in air and rinse much later.
An important part of the process is to whisk the dye bath after addition of soda crystals at 50 deg. Bubbles take a while to form and must be whisked continuously to achieve a foam over dye bath. It may be cream, or slightly green coloured. Blue-green is described in recipes but dull cream still gives a blue result. Click to enlarge.
1st Session: Images 1 - 9 - Turquoise blue achieved, but was lost after returning to dye bath.
2nd Session: Images A - J - Same procedure as 1st Session, turquoise blue achieved, and kept. Additionally third dye bath with added iron which darkens and greys silk.