I went to the Natural Dye Group meeting (every 3rd Friday; 7-10 pm) in Alexandria. Only Sylvia del Mar was there. No else was expected as it was close to Christmas. I thought I'd just watch and kibitz, but brought Wensleydale, BFL and ginned cotton anyway. Good thinking.
Sylvia brought out reference books for me to have a look at. The most beautiful was the Indigo Madder & Marigold: A Portfolio of Colors from Natural Dyes by Trudy Van Stralen. Mental note: got to get a copy. Then she introduced me to the powdered mordants in thigh-high bins: alum, soda ash, urea, ... no chrome because it's not good for the environment. There were other stuff overhead for thickening dyes for use as fabric paint.
So we dipped wool in an alum solution. Since I ohhhed and ahhhed at the pictures of bright pink in the Van Stralen book, Sylvie picked brazilwood powder. Heat water for a minute in the microwave, dissolve some brazilwood powder, reheat again for another minute. If you alternately add vinegar and ammonia, the afterbath will turn into red-orange, magenta, and back to red-orange like magic. We divided the afterbath into two plastic cups: one red orange and one magenta. Squeezed out the mordant liquid and divided the fiber between the cups. More heat in the microwave, about three minutes each, as long as the plastic cup did not melt.
Sylvia made me pinch out a tiny piece of each color and blotted it to dry. It was to be stapled onto an index card with notes of date, dye, solutions and time in the afterbath.
When it was done, we covered the cups for me to take home and soak overnight. The fibers are to be taken out of the afterbath, squeezed and dried before washing.