One of the very few dyes that can be used reliable as a pigment comes from the woad plant (Isatis tinctoria). It is also sometimes called wild mustard. This spring my wife planted a small crop for me in her garden and with the weather turning cooler I thought it was time to harvest some of it.
My son was a big help as he carefully cut each leaf and placed it into our collection bag. Any leaf that was dried out or had any blue colouring had to be rejected (this is because once the blue is visable within the leaf no pigment can be obtained). Although it was a cool morning, we both enjoyed the work.
After cleaning the leaves and tearing them up we placed them into a big pan of 80C hot water. After ten minutes or so I removed the leaves and wrung them out. By this point there was an overwhelming smell of spinach in the air!
It took much longer than I had thought I would to cool down to 50C, even with the cool air outside. Once it did come down, I added a little bit of Sodium Carbonate that had been dissolved into a cup of boiling water. Now it was time to aerate the liquid.
Once that work was done, and the froth had settled down, the water had a dark blue-black colour when stirred.
That is all I can do for now. Hopefully there is pigment in there and it will settle out over night.