Turning it blue on the catwalk

Biochemists are refining the production of natural indigo from woad. The dye was once extracted from the leaves of woad (Isatis tinctoria), but purity was routinely less than 50 per cent, compared with synthetic indigo, which is over 90 per cent.

Philip John, professor of plant biochemistry at the University of Reading, UK, reports that the interaction between newly formed natural indigo and particulate contaminants is key. To produce the dye, leaves are soaked in warm water to extract the indigo precursors - isatans. Adding alkali to the water releases free indoxyl, which forms indigo after shaking.

The team used indoxyl acetate hydrolysis as a model for isatan hydrolysis and studied the effect of leaf contaminants on indigo yield. Adding soil or woad extract reduced yield, a finding the researchers attribute to hydrogen bonding between contaminants and dye.

The study was funded by the EC Spindigo Project, which supplies natural indigo to companies such as aptly-named fashion house Boudicca. Warrior queen Boudicca and her troops reportedly rode into battle painted with woad.

Bea Perks