Copper, in the form of copperas, vitriol, verdigris, and others, has been employed as mordanting and dyeing agent for more than 4000 years. It is particularly useful to assist the development of blues and greens, and is a good mordant for increasing color fastness.
Instead of buying copper sulfate or another form of chemical copper, go to the grocery store and buy 3 copper pot scrubbers, the kind without soap. Simmer in 1/2 gallon of water with 2 tsp of ammonia for 2 hours, then cool and allow to steep for several days. Add fiber, simmer for 15 minutes, cool, then rinse fiber with vinegar and water.
Copper is poisonous; however, there are several varieties of garden plants, among them rhododendrons and azaleas, that thrive on copper based fertilizer. To dispose safely of the mordanting fluid, dilute with lots of water and pour at the base of the plant.