Indigo carmine is a dye that, following its introduction, was often used to dye textiles and to stain leather and furniture despite its poor properties. The development of this semi-synthetic dye cannot be underestimated, since it caused a revolution in dyeing technology. Until then, Indigo, the only stable blue dye, was extracted from natural sources such as Woad (Isatis tinctoria L.) or Indigo (Indigofera tinctoria L.), so-called vat dyes. The dye extraction was very laborious and included complicated fermentation processes, a procedure which could easily take days or even weeks. Dyeing was also very time-consuming as the insoluble main component, indigotin, needs to be converted into the soluble leuco-indigotin form first. Indigo carmine, however, is a water-soluble acid dye. As such, the dye can be easily dissolved and it binds directly to the textile fibre; the dyeing itself only takes minutes, a tremendous advantage compared to the laborious procedure required for Indigo. As a result, Indigo carmine was often used to dye blue or mixed with yellow dyes to obtain green.