Abstract
Indirubin dyeing with fresh leaves of Polygonum tinctorium under acidic conditions was investigated. In the case that indoxyl was oxidized under acidic conditions below pH 2, a significant amount of indirubin was yielded in addition to indigo. By applying the results to dyeing, the following new methods of indirubin dyeing with Polygonum tinctorium were established : 1) Dyeing with the fresh leaves in the presence of ethanol (20%) under strong acidic conditions; 2) Dyeing with the precipitate of indigo and indirubin which was produced by hydrolysis of indican from the fresh leaves with citric acid (0.5-1.5 mol/l) at an elevated temperature; 3) Dyeing in an acidic solution of indican from the fresh leaves at an elevated temperature; and 4) Dyeing in a cooled solution of indican which was heated with citric acid. In the case of 4), in addition to silk, cotton could also be dyed purple. Methods 2), 3), and 4) are par-ticularly useful because indirubin can be dyed only with fresh leaves of indigo plants and citric acid.
