WATER EXTRACTION METHOD
There are two main methods of producing indigo dye from plants: the water extraction process and the composting process. Both methods serve to convert the indican that occurs naturally in the plant cells into a usable dyestuff.
The water extraction process is a liquid state extraction process that yields a powdered pigment with high indigotine purity. The pigment extraction requires the indoxyl reduction to be oxidized in order to manifest the pigment. The basic steps of water extraction include extraction, oxidation and filtration.
The indigo pigment extraction should be started immediately after harvesting in ordert to avoid reductions in indigo content. Prior to extraction, we rinsed the Persicaria plants in clear, cold water to remove any soil particles or insects that may be adhering to the plant. We immersed the plants in batches in a cold water bath, agitated them briefly, took them out and drained them. After that we were soaked the plant material in water and then exposed to the sun to start the fermentation process to release the soluble form of indigo (indoxyl). Fermentation pulls the indigo precursor indican out of the plant cells and into solution where indican undergoes hydrolysis and cleaves into indoxyl and a sugar.
The plant material should be completely submerged to limit exposure to oxygen. We used heavy stone slabs and canisters filled with water to keep the plant material below the surface of the water. Preferably, plants are only compressed enough to remain below the water surface to limit the exposed liquid surface and the entry of atmospheric oxygen into the liquid.