The Rug Library

Mordant dyes such as madder, lac and cochineal have little direct affinity for fibre and bond instead to fibre pretreated with a metallic salt such as aluminium, iron, chrome or tin.

A scientific study of a 16th-century carpet with chintamani motifs used chromatographic and spectroscopic methods to identify its natural dyes, uncommon dye components and mordants.

William Henry Perkin, then 18, produced mauve (mauveine) from coal-tar chemicals in 1856 while trying to synthesise quinine; it became the first commercialised synthetic dyestuff.

After patenting mauveine in 1856, Perkin opened a dyeworks at Greenford, near London, the following year to mass-produce it, helping launch the synthetic dye industry.

'Abrash' is the term for visible shifts of shade within one colour area of a handmade rug, often appearing as bands, caused by differences between dye lots or batches of wool.

Indigo is insoluble in water, so for vat dyeing it is chemically reduced in an alkaline bath to a nearly colourless 'leuco' form that fibres can absorb.

When yarn is lifted out of an indigo vat, the absorbed leuco dye re-oxidises in air to insoluble blue indigo, which is why colour develops after dipping; repeated dips build a deeper shade.

The colour a mordant dye gives can vary with the mordant and binder used; purified lac dye, for example, can yield hues from crimson to deep pink.

Not every natural dye needs a mordant: turmeric colours cotton yellow directly, unlike mordant dyes such as madder or lac.

Lac dye was not imported into Europe in commercial quantities until the late 18th century, and synthetic red dyes introduced some decades later made it largely obsolete.

Many artisan dyers use turmeric in a weakly acidified bath without heat or a metal mordant, reflecting how easily the dye takes up on fibre.