In 2017 I participated in a Ecoprint course at Spektrum in Denmark. (www.spektrumtextil.dk).
I learned to getting color to adhere permanently to fabric as silks and wools, and at the same time get imprints from plants.
It is a slow process and it is very exciting to see the results, because you never know how the plants react every time.
Kirsten Lundberg taught me this fascinating technique over 3 days.
Shortly the technique: Dip a silk textile in Ferro- or Copper solution, do the same with your chosen plants, cover with a cotton textile dipped in the Dye. Roll up your plant materials tightly and wrap with string a bundle around a stick. The string will act as a resist, leaving it’s marks on the fabric. Then steam your fabric for 90 minutes.
Leaves with tannins are best for ecoprinting, and the leaves of autumn seem richer after a season of photosynthesis than the young leaves of spring.
I have developed the imprints more with gouache paints.