The light-fastness of textiles dyed with 6,6′-dibromoindigotin (Tyrian purple)

The colourant in the ancient dyestuff Tyrian purple is predominantly 6,6′-dibromoindigotin. The light-fastness of a synthetic version of this dye was investigated by dyeing six different textile types and subsequently performing accelerated light fading. The hue of the samples were measured using the CIELab system and fading rate constants derived for each sample. A range of samples of different initial shades of dyeing were obtained so that, for each fibre type, characteristic curves could be obtained showing the way initial depth of shade of dyeing varies the fading rate. All dyed textiles were most light-fast at deeper shades. Of the various textile types, dyed wool was most light-fast followed by silk, linen, nylons 6 and 66 and finally cotton.