Dyestuffs

Dyestuffs are substances used to impart color to materials such as textiles, leather, paper, plastics, and foods. In textile chemistry, dyes are typically soluble compounds that form a bond with the substrate, unlike pigments which are insoluble particles. Dyestuffs are broadly classified as natural or synthetic.

Natural dyestuffs come from plants, insects, or minerals and include indigo, madder, saffron, logwood, and cochineal. Synthetic dyes emerged in the 19th century, starting with mauveine, and expanded into classes such as azo dyes, anthraquinone dyes, reactive, and vat and disperse dyes. Synthetic dyes offer broader color ranges and improved fastness.

Dyeing involves dissolving the dyestuff in a bath with the substrate, often aided by mordants or auxiliaries to improve adhesion and colorfastness. Mordants like alum, tannins, or iron compounds can form coordination complexes with certain dyes to fix them to fibers. Substrates include cellulose fibers (cotton, linen), protein fibers (wool, silk), and synthetic fibers (polyester). Fastness properties include lightfastness, washfastness, rubbing fastness, and heat stability; these vary by dye class and substrate.

Environmental and regulatory considerations address dye manufacture and wastewater, as some dyes are toxic or persistent. Efforts focus on safer dyes, wastewater treatment, and dyeing processes that reduce chrome or aromatic compounds. The field continues to balance performance, cost, and sustainability.