A mordant is one of the first steps in natural dyeing. It allows the fabric to accept or bond with the dye. The word is derived from Latin 'modere' - meaning 'to bite'. Essentially, it enables the dye to 'bite' into the fabric. Without a mordant, colors will simply wash out. This mordant kit is for cellulose fibers (cotton, hemp, linen) and contains 90g each of Aluminum acetate (alum) and Calcium carbonate (chalk), along with instructions. It will mordant approximately 4lbs. of cellulose fabric. Alum is very dusty - please wear gloves and a dust mask when opening packet, and allow for plenty of ventilation while working.