A natural or synthetic substance used to add a color or to change the color of something. Dyes are the coloring material that color commodities of our day to day use. Dyes are applied everywhere, from Plastic toys for children to that fabrics you wear, from food to wood; hardly there is any industry where dyes are not used commercially. A dye is a colored substance that has an affinity to the substrate to which it is being applied. It is an ionising and aromatic organic compounds. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.