Indigo dye, a natural dye that requires either natural fermentation or a chemical based environment to become active. There are several online resources that will do better justice than I can:
- Link to online scanned copy of Shibori: the inventive art of Japanese shaped resist dyeing, starting at page 275
- Link to Maiwa indigo data sheet
- Link to a blog from a gentleman living in Japan who maintains natural indigo pots and often provides some insight to his technique
- Link to my weaving instructor's blog who also does indigo and other natural dyeing
Enter the beautiful world of indigo, it is a fascinating place.