In June and July we held a Six Weeks of Blue: Indigo Dyeing workshop led by Ulrike Bogdan. Ulrike provided comprehensive instructions to make several different kinds of indigo vats with fresh leaves and natural indigo. She began by telling us a bit about plant dyes using lovely analogies and why indigo is so special... then, on to the practical reduction and fermentation vats before exploring painting techniques using oxidised indigo. She also explained that while all indigo is chemical, the sources are different, natural indigo is derived from plants while synthetic is produced from petrol but good results can be had from both. The use, preference, environmental impact and sustainability is a whole other discussion.
Indigo vats are all about the senses, so questions and the sharing of photos flourished in this workshop.
Right: Carolyn Arber from Birmingham, UK, posted this picture showing the effect of reducing with sodium dithionite. The liquid changes from dark green to yellow as the indigo becomes soluble.