Found this http://www.saltspringweaving.com/blog/?p=1155#comments that mineral clay dyes were used while looking up Saori weaving that looks so fun. Saori is weaving your self and no rules or wrong.
The Bengala Dyes do stay on the yarns after washing - they are wonderful colours. You can read more about the Bengala Dyes on Chiaki & Dan's website (they were the workshop teachers here at the workshop) - http://saoristudiofun.com/bengala-dyes/. You can also see the Bengala Dye colour chart for the numbers of the various colours.Happy Weaving,Terri