Bello Marini*: Tie-dyeing in Indigo (mostly)

Indigo Quality key

Contents

Indigotin Blue Dyes

Introduction

A number of plants of several different families contain the compounds indican or isatin, both of which ferment to form indigotin (indigo, indigo blue) and indirubin (indigo red).

"Indican appears to be a by-product of the plant's metabolism and to be not particularly stable for in harvesting the stem of the plant it is necessary that the leaf be immediately subjected to bacterial action lest it disappears. The normal commercial process requires that the stems be submerged in water in a suitable vat contaminated with bacteria for a period of 10-15 hours during which time the indican is hydrolysed to glucose and indoxyl which pass into aqueous solution. The liquor is separated and aerated by beating to promote oxydation [sic] of indoxyl to indigotin, or indigo-blue, which settles out as an insoluble faecula at the bottom of the vat." (Burkill 95 v.3 p.363)
"Indigo-blue [indigotin] and indigo-red [indirubin] are isomerous, but not interchangeable. Their proportions vary according to the conditions of the processing. Slow oxidation in an acid medium favours the latter, while rapid oxidation in an alkaline medium the former." (Burkill 95 v.3, p.363)
--Perhaps indirubin would come out more if the cloth were sunk in a vinegar (or other acid) bath after each dip immediately upon removal from the vat and kept immersed until oxidation finished. A good soak in a lye or lime and powdered limestone bath would be needed to neutralize it before re-dipping into the indigo vat. It would not take very much acid to screw up the vat.

Indigotin Production from Plant Material

Steeping and Precipitation Method

Method 1: Based largely on The Woad Page: Processing by

  1. Chop up freshly cut leaves (and stems in some species) fairly finely and put them into a container that can withstand heat (large glass jars are good)
  2. Pour enough boiling water to cover the leaves into the jar. Cover and let stand for about an hour.
  3. Strain the liquid through muslin to remove all plant bits.
  4. Add alkali (lye, potassium hydroxide, lime, or ammonia) to the strained liquid to reach a pH of 9 or higher. If you don't add too much alkali at a time you can test it by hand--your fingers will feel greasy or soapy starting around pH9-10. Have some vinegar standing by to rinse your fingers with.
  5. Use a whisk, egg beater or electric blender to mix air into the liquid. As you do this the indigo will oxidize and come out of solution.
  6. Allow the liquid to sit until the blue indigo has sunken to the bottom of the container.
  7. Carefully pour the liquid off the top, leaving the precipitated indigo in the bottom. Add more water and repeat to rinse the indigo.
  8. Pour the indigo into a shallow pan (preferably non-stick) to evaporate.
  9. When indigo has dried you can grind it and use it just like any other indigo.

Variation: Use lye or potassium hydroxide as the alkali in step 4 above and then add hydrochloric acid to oxidize and precipitate the indigo, instead of the whisking of step 5. (Based on A Modern Herbal: Woad: Treatment of the Crop)

Mound of Goo Fermentation and Couching

Based largely on A Modern Herbal: Woad: Treatment of the Crop

  1. Dry the freshly cut leaves very slightly in the sun.
  2. Pound or grind them into a paste consistency.
  3. Form paste into a mound outside in the air, but protected from rain.
  4. Do not disturb the mound for about two weeks as it ferments--especially, do not break the crust that dries on the outside
  5. After about two weeks mix the paste (and crust) together and form it into lumps or cakes
  6. Dry the cakes in the air
  7. Before using the dye break up the cakes, mix them with water to form paste, and ferment them again
  8. "The colour is brought out by mixing an infusion of the Woad thus prepared with limewater"--probably meaning you should then treat the fermented paste like the fresh leaves in the Steeping recipe above (pour on boiling water, let sit, filter/decant, add alkali, beat in air to oxidize, let indigo settle, decant, rinse, decant, dry)

Variation: Skip steps 6 and 7; just use the mixed fermented paste of step 5 in step 8. (Based on A Modern Herbal: Woad: Isatis indigotica, Chinese)

Processing Woad from the Woad Beta-FAQ

Indigo from Woad experiment

Indigo Vat Types and Recipes