Classification of dyes according to their application
Direct dyes:
this type of dyes can be directly applied to the fiber, both vegetable and animal, by dipping in hot aqueous solution of the dye. This type of dyes is most significant for those fabrics that can form hydrogen bonds, that is for rayon, wool, silk, cotton and nylon. Congo and Martius yellow red work as direct dyes. Instances are: Martius yellow, congo red.