Some Notes on Indigo Dyeing using Fermentation Vat
1. Indigo itself doesn not exist as such in nature. It is easily formed by oxidation of a a part of plant called IndigoFera by exposure to air.
2. Simply speaking, Indigo itself is a blue solid. It is insoluble in water, acid and alkalies. If Hydrogen is added to it, or chemically speaking it is "reduced" by many reducing agents- It changes to "Indigo White" which is colorless. This indigo white can dissolve in water, in presence of alkalies, to a bright yellow liquid. When Textile substance is dipped in it and exposed to air, white indigo takes up oxygen and get converted into blue coloring matter.
3. In fermentation method water is made alkaline with the the addition of Lime or Alkali. Then substances are added which can ferment easily in the presence of alkali, for example wheat bran (madder is added to expedite the fermentation). It takes about two to three days to ferment and then indigo is added. This bath can be used for several days or even weeks. Fresh indigo and other ingredients are added from time to time. The color of bath is light greenish yellow in color with a blue or bluish green scum. Goods immersed in this bath turns yellow. When they are taken out and exposed to air, the yellow color quickly changes to blue.
3. The color of the bath is very important. If it is bright yellow, it means too much alkalanity and more indigo should be added. If the color is too dark, it needs more lime or other alkali.
4. After the color has changed, the goods should be rinsed well in two or three waters. After that should be boiled for several minutes in a soap bath to washoff the loose dyestuff and prevent rubbing. Rubbing can also be prevented by building up deep shades by successively dippings in the moderately weak vats, rather than obtaining the shade once for all.
Here are some tips (Source)
1. Keep the vat covered. The level of water in the pot should be to the brim.
2. Wet out your fibers well. Any air remianing in the fiber will oxidise the indigo in the vat.
3. Enter the fiber into the vat very carefully, to avoid any air in the wet.
4. Always work under the vat.
5. For greens, dye with indigo first. Then rise well and overdye with alum mordant and any yellow dye ( traditionally Turmeric). For purples, dye the Indigo first, rise well, mordant and dye with any red dye.
Remember, you can use various chemicals to reduce the indigo vat. The alkalnity of these chemicals vary from Soda Ash ( Sodium Carbonate), Slaked Lime ( Calcium Hydroxide), Sodium Hydrosulphide to Caustic Soda ( Sodium Hydroxide) in that order(from low to high).
Sources
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