Vat dyeing

Vat dyeing colors fibers by reducing an insoluble dye to a soluble form, applying it, then oxidizing it so the dye becomes insoluble inside the fiber.

Reduction: A chemical process in which a substance gains electrons or loses oxygen. Vat dyeing reduces the dye into a soluble form that can enter fibers.
Cellulose: A structural polysaccharide that forms the main component of plant cell walls and cotton fibers. Cotton’s cellulose structure readily accommodates many vat dyes.
Denim: A sturdy cotton twill fabric, commonly woven with indigo-dyed warp yarns. Indigo vat dyeing gives denim its characteristic blue surface and fading behavior.
Reactive dye: A dye that forms a covalent bond with a textile fiber during application. Reactive dyes bond chemically to fibers, while vat dyes are fixed by becoming insoluble.
Washfastness: A textile color’s resistance to fading or bleeding during laundering. The dye’s insoluble oxidized state helps vat-dyed fabrics retain color through washing.
Oxidation: A chemical process in which a substance loses electrons or gains oxygen. Air or another oxidant restores the dye’s insoluble colored form after application.
Indigo: A blue organic pigment historically obtained from plants and now also made synthetically. Indigo is the best-known vat dye and illustrates the reduction-and-oxidation sequence.
Cotton dyeing: The application of colorants to cotton fibers, yarns, or fabrics. Vat dyes are valued for coloring cotton with strong wash and light fastness.
Direct dye: A water-soluble dye applied directly to fibers, especially cellulose, without a mordant. Direct dyes can be applied from solution without the reduction and oxidation required here.
Fading: The loss of color intensity in a material through exposure or use. Indigo’s surface-heavy deposition makes its fading especially visible in worn denim.

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