INDIGO PLANT AND DYE. Like what was used to dye blue thread, Exodus
How to Make Your Own Natural Indigo Dyes (http://blog.hgtv.com/design/2011/09/07/make-your-own-indigo-dyes/?soc=Pinterest)
Extracting natural blue pigment from the leaves of the Woad plant. The pigment has traditionally been used to dye wool but it can also be used in naturally colouring soap.
Indigofera tinctoria - Indigo plant
Culture Of Indigo: Plant, Product, Power
Each dip accumulates more pigment on the fabric. This stepped cloth shows the saturation from 0-10 dips in an Iron Vat.
Growing Indigo (Polygonum tinctorium) | :: Rowland & Chinami Ricketts
Before Indigo was used, "woad" was used. "Woad is an old color. A conversation with history. A natural dye. An ugly plant. Locked in green leaves, compounds that break into pigments of blue." -Curious Blue | HandEye
Planting a Dye Garden to Make Your Own Natural Dyes
Kate Bowles Books : More Indigo (and a few things from my compost bin)