Recently, we attended an indigo dyeing workshop here in Provence. It was hosted at a beautiful art center in Aix-en-Provence, Hôtel de Gallifet (which should definitely make your list of places to visit in Provence).
The actual dyeing process was fascinating. We each came with a cotton, silk or linen article of clothing. We spent time folding, binding with rubber bands or wooden blocks the fabric to create patterns, or spaces that would resist the dye.
We immersed the articles in pure water and wrung them out so they were not dripping wet. Then we submerged the fabric in several rounds in the vat of indigo.
The fabrics would at first come out yellow-green, but when mixed with the oxygen in the air, the fabric would turn blue. A deep indigo color is achieved through many rounds of immersion, with rest periods in between.
For more information on the art center and the workshop: visit this link.