Dyeing

Dyeing is the process of imparting color to materials such as textiles, leather, paper, or plastics by applying soluble colorants that attach to or become embedded in the substrate. In textiles, dyeing typically involves immersing the material in an aqueous dye bath containing a dye, auxiliaries, and heat to promote uptake and fixation. The resulting color can be influenced by fiber composition, dye chemistry, temperature, pH, and time. Dyeing differs from printing, which places color only on the surface.

Natural dyes, sourced from plants, minerals, or insects, have a long history but can pose reproducibility challenges. Synthetic dyes, developed in the 19th century, provide broader color ranges and consistent performance. Dyes are chosen for their affinity to specific fibers and often require mordants or specific pH and salt conditions to improve fastness. Major dye classes include reactive and direct dyes for cellulose, acid dyes for protein fibers and nylon, disperse dyes for synthetic fibers like polyester, vat dyes for cotton, and sulfur dyes for dark shades.

Dyeing can be performed at multiple stages, including fiber dyeing, yarn dyeing, piece dyeing (fabric), and garment dyeing. Common processes include exhaust or batch dyeing, where color is absorbed into the fiber over time and temperature, and continuous dyeing, in which fabric passes through a series of dyeing and washing stages. Key qualities include wash fastness, light fastness, and rub fastness, which depend on dye-fiber affinity, mordant use, and finishing treatments. Environmental considerations center on wastewater treatment and chemical management.