Overview

A dye is a substance used to impart color to a substrate by chemically or physically bonding to it. Dyes are commonly applied to textiles and clothing, but also color paper, leather, hair, foods, and some plastics. Unlike pigments, which remain as discrete particles, many dyes dissolve or disperse and interact with the material’s fibres so the color becomes an integral part of the item. For a concise definition see definition and for textile uses see clothing and fabrics.

Types and sources

Dyes can be grouped by origin and chemistry. Natural dyes are derived from plants, animals and minerals — examples include indigo (from plants) and cochineal (from insects). Plant parts used for natural dyes include roots, bark, leaves, fruits and wood; fungi and lichens also supply traditional colors. See sources: plant parts, roots, fruits, bark, leaves, wood, fungi, lichens. The majority of modern dyes are synthetic, produced through chemical processes often starting from petrochemical feedstocks; see a note on industrial origins: petrochemical sources.

Characteristics and major classes

Dyes differ in solubility, fastness (resistance to washing, light and rubbing), and the manner in which they bond to fibres. Common classes include reactive dyes, direct dyes, vat dyes, acid dyes and disperse dyes, each suited to different fibres (cotton, wool, silk, polyester). Some dyes require a mordant — a chemical that fixes the dye to the fibre — while others form covalent bonds during the dyeing process.

Processes, applications and examples

Dyeing methods range from batch and continuous industrial processes to hand-dyeing and artisanal methods. Industrial applications include textile mills, leather finishing and colorants for plastics and inks. Small-scale and historical practices emphasize local natural materials and traditional techniques; see general usage notes: solubility and application.

Environmental and practical considerations

Dye production and effluent management raise environmental concerns: some synthetic dyes and auxiliary chemicals can be toxic or persistent in water, so treatment and greener chemistry have become priorities. When comparing dyes to pigments, remember that pigments do not dissolve to bond with fibres and therefore serve different roles in paints and coatings; see contrast: pigments versus dyes.