Today I went to the centennial celebration for the Fairbanks Experiment Farm, not something I'd ordinarily do, except that for the last four years I've been working for the School of Natural Sciences & Agricultural Sciences (fondly known as the School of Ag!), so I've been involved in all kinds of things agricultural and naturally scientific. So I was working today, setting up displays, carting water and lettuce seed packages, making signs, etc. There were several demonstrations and activities throughout the day, including one done by Gail Mayo on dyeing with natural plant dyes. I didn't recognize her at first, it's been so long since I've seen her.
She had a little propane stove set up with a couple of pots of plant part stew, with hanks of wool from her own sheep. She sends the wool Outside to be spun at a mill that creates a characteristic almost plaited, knobby sort of yarn. It's very nice yarn (I have some myself from when she was selling it: Tanana Wool). She also had numerous samples, mostly in yellows and browns, but a few greens and blues and reddish dyed bits of wool, too. The mordant she used for most of them was alum. Other things can be poisonous: chrome, tin, copper. The alum is apparently fairly innocuous. She also uses vinegar for some dyes.
I don't know much about dyes and mordants, but it's always intrigued me.