Aluminum Potassium Sulfate or "alum" is frequently used by dyers. It improves light and wash-fastness of natural dyes. Using alum as a mordant keeps color clear and can be used with both protein and cellulose fibers. Use at 10%-20% WOF. Available in 8oz.
May we suggest the perfect pairing?
Natural dyeing with plants by Franziska Ebner + Romana Hasenohrl