indicant. Indigo is formed form indican by fermentation of plant material such as Baphicacanthus cusia Brem., Indigofera suffruticosa Mill, Polygonum tinctorium Palette, Isatis indigotica, Fort ect. Followed by air oxidation of indoxyl. Indigofera tinctoria contains isatan B , as a major indigo precursor and indican as a minor indigo precursor.