This dye substance is not a plant, but it would have been available in one form or other to many colonial home dyers. Known as “Copper Penny Blue”, this is a dye that does not need a separate mordant or even heat. The recipe is simple but it does take from 2-4 weeks for the process to complete itself. Fill a gallon jar to about three inches from the top with non-sudsing ammonia and put in: either 2 cups of pennies, OR a length of copper pipe OR a coil of copper wire. Screw the lid on tightly. Let this mixture sit for a week and watch it become a beautiful blue. At this point remove the copper , with rubber gloves, and put in the pre-wetted fleece to soak; varying the time gives different color effects. Some sources say it is also possible to do this with white vinegar instead of ammonia, but others say vinegar doesn’t work as well. Some recipes say to add a few teaspoons of salt to fix the color.
I’ve used this method several times with different results. One was a pale aqua, and the others various shades of icy green. I think it might be more reliable to use wire or pipe as the amount of copper in pennies these days is so small. Dyeing times, once the dye is made, have ranged from 1 day to 3 weeks of soaking the wool fiber. If you leave the jar in the sun it speeds the process somewhat. I would NOT try heating the mixture on a stove or fire, however.
My results have always been close to this.
Post revised 8/28/20