Red and grey fabric dye box with a paper dye packet containing Rit brand, all-purpose grey powdered fabric dye. All-Purpose Rit dye was introduced in 1941. This development gave the dye an affinity for synthetic fabrics, like nylon and rayon. Prior to this development, Rit dyes had only been successfully used on natural fabrics (like wool, cotton, linen, and silk) and did not work effectively with synthetics.

Dyes are charged, water-soluble, organic compounds that chemically bind with fabric. The affinity of the dye for the fabric depends on the molecules and the interactions between them. To improve the binding affinity, an additive called a mordant may be added to the solution. A mordant contains metallic salts, which provide a connection between the dye and fabric molecules.