They did use synthetic dyes however, because their research indicated that they resulted in 75 % less unused dyestuff in the effluent and created siginificantly less water and energy consumption. (treehugger.com)
Light, particularly ultraviolet, destroys the pigments in natural dyestuffs and damages the materials. (newscientist.com)
Environmental campaigners Evergreen agree: «If everyone in the UK bought one reclaimed woollen garment each year, it would save an average of 371 million gallons of water (the average UK reservoir holds about 300 million gallons) and 480 tonnes of chemical dyestuffs.» (dailymail.co.uk)