Indigo (indigofera tinctoria)

Color: Light blue to navy

Source: fermented leaves

Note: Indigo is a vat dye and should be dyed accordingly.

1. TEMPERATURE required in the dye-pot is fiber related:

Protein fibers (wool and silk) need a temperature of 125 °F
Cellulose fibers (cotton and rayon) need a temperature of 100 °F

2. pH of the dye-pot needs to be alkaline (>7); the desired value depends on the fiber being dyed:

Protein fibers (wool and silk) require a pH of 9.5-10
Cellulose fibers (cotton and rayon) require a pH of 11

The pH of the dye-pot is adjusted using lye (increases the pH) or lemon juice (decreases pH).

3. The dye-pot solution is reduced of oxygen by using Thiourea Dioxide. Fabric or fiber is dipped in the pot and will oxidize and turn blue when exposed to air.

Steps for Indigo Dyeing

1. Make stock indigo solution (instructions follow)
2. Prepare material to be dyed. Wash fibers/fabrics (skein yarns to prevent tangling). Keep material wet (recommended but not necessary)
3. Prepare dye pot (instructions follow)
4. Dip material in indigo pot (2-10 minutes). Keep submerged. Rotate gently to avoid introducing oxygen.
5. Remove fabric/fiber from pot to oxidize (20 minutes minimum)
6. Re-dip if desired. In order to get dark indigo a series of dips are necessary.
7. Aerate 24 hours minimum after last dip.
8. Neutralize in vinegar solution.
9. Wash in hot soapy water

Indigo Stock Solution

1. Use a 2-quart wide-mouth jar with secure lid.
2. Put about 2 oz. (about ½ cup) natural powdered indigo into the jar.
3. Add about ½ cup warm water and stir to make a paste.
4. Add 3 more cups warm water and stir.
5. Add in 2 tablespoons sodium hydroxide. Stir gently.
6. Add in 2 tablespoons Thiourea Dioxide. Stir gently.
7. Let stand 15 minutes, uncovered.
8. The stock is now ready to use. Cover and store until ready for use.

Indigo Dye-Pot Preparation

1. Fill dye pot with water. Adjust temperature for fiber type.
2. Add Indigo stock (½ – 1 cup depending on pot size)
3. Add 1 tablespoon Thiourea Dioxide. Stir gently. This reduces the oxygen in the dye-pot. A reduced dye-pot will change color to a greenish/yellow. If the pot is blue add Thiourea Dioxide. If pot is very yellow add oxygen by stirring.
4. Check pH of dye-pot for fibers to be dyed. Add sodium hydroxide to increase pH. Add lemon juice to decrease pH.
5. Monitor dye-pot continuously to maintain a balanced dye pot. If your pieces bleed or rub off at least one variable was not maintained curing the dye process.
6. Replenish pot with more stock solution as strength decreases.

Preparing an indigo pot takes practice and is affected by variables such as type of water.  Please use the recipes as guidelines and adjust the amounts of chemicals needed for your dye pot.