Natural dyeing is a multi-step process. Altering applications in each step may affect parameters like the shade of color or fastness. Thus, creating dyeing recipes is an arduous process in which the best conditions for dyeing are determined by testing each parameter separately.
Natural dyes are organic substances that play various roles in plant metabolism and generally have antioxidant and antibacterial properties. In order to make these substances bind to fibers, non-toxic metal salts which are called mordants are used.
I usually prefer using Potassium aluminium sulfate, alum, for mordanting. It is also possible to obtain different shades from the same plant material by using copper and iron salts instead of alum.
Alum is not a toxic chemical however, it increases the salt level of the soil, so I pour the liquid waste down the sewer. On the other hand, I always recycle the waste plant material back to soil. In regard to toxic properties of synthetic dyeing processes, the footprint of sat-su-ma products on nature is quite small.