Polygonum tinctorium from my own garden (not the 'real' indigo, it's also known as Japanese Indigo) - filled me with an exitement which can only be compared with the exitement I felt as a child before yule. And it smells so good too!
I trimmed off the leaves and put them in the food processor with some cold water. Let it soak for half an hour with some vinegar added to the solution, then strained the liquid through a silk scarf and squeezed the pulp thoroughly. Added some more cold water and a bit of vinegar to the pulp, same procedure as before. Then the wetted yarn and sik scarfs were added to the dye bath. I let it soak for an hour, stirring occasionally. Squeezed it and let it hang to dry. It was wonderful to see the blues develop - slowly before my eyes.
Polygonum tinctorium. Number two from the top is the one used to strain and squeeze the liquid. It's a very strong turquoise. Number three and four is over dyed, ivy and birch leaves, I believe.
I really recommend trying to dye with this plant! It was easy to grow, the seeds sprouted right away (sowed in pots inside) - and I didn't do anything but planting them in a mostly sunny spot with lots of manure. We had a pretty cold, wet summer which they apparently liked.
The dyeing process was easy and fun. No boiling, chemicals or synthetic additives. Organically grown leaves, cold water and vinegar, that's all. And no stress or rushing, I baked a cake and made apple butter while dyeing.
I had to dig up and bring a couple of plants indoors, hoping they will make seeds for sowing next year. Fingers crossed!