I had no idea natural dyes from everyday plants such as buckthorn (an invasive species), hollyhock, and tansy would produce such an array of colors—and so easily! Mostly it was like brewing tea, with a fixative—alum, the same as you use to make pickles.
DO NOT HARVEST LICHEN, the teacher said. It is too fragile and too slow-growing a life form to survive much harvesting.
It's sad you can't harvest lichen because, most astonishingly to me, this particular lichen soaked in ammonia water for six months made a dye that turned the yarn pinky-purple and the cotton a deeper purple.