Who doesn't want to create their own blue jeans dyed with their own home-grown and processed indigo? Well, I am one of those people. This spring I received 2 flats of tiny seedlings from Craig Wilkinson through my Fibershed connection. I planted them in my vegetable garden, easily forgoing the zucchini that would subsequently be given away anyway. The Polygonum tinctorum is Japanese indigo, more appropriate for Sonoma County than Indigofera tinctoria grown in India and elsewhere in tropical regions.
What are we after? 3-12 grams of "indigo carmine" or indigo will dye a pair of blue jeans from baby blue to super dark. Each leaf of the plant can contain 0.2-0.8% of indican, the precursor. So those plants are serious about creating that compound.
Let's go through the chemistry because it is so fun. I can now understand the enticement of chemists and alchemists by swishing around a huge vat of extract and watching instant color changes. The precursor to indigo is indican, curiously colorless and water soluble. It is derived from the amino acid tryptophan. Remember the "natural" product that was supposed to help you sleep back in the 80's? Some contaminant caused a horrible rare side effect called eosinophilia-myalgia syndrome in 1989. That is always the first thing that pops into my head when i hear the word tryptophan, but fortunately I never saw a case.
First, pop leaves into water and let them stew in the warm sun for a week to extract the indican. Hydrolyze and release b-D-glucose and indoxyl. I did this by raising the pH from neutral to 10 with 100 grams of Lye, potassium hydroxide, mixed into 200 liters of water. Oxidize by vigorous stirring and convert the indoxyl to indigotin, the endpoint of indigo dye.
Next blog, cliff hanger, covers enticing the insoluble indigotin to link up with fiber (wool, cotton. or silk for example) to create beautiful blues. The molecule is large and perches on the outside of the fiber. Hence, stone-washed jeans can be embellished with pale patches by literally sanding off the outer edge of the fibers revealing the lighter undyed core. It was supposed to emulate hard work, but the patches to not correspond to anatomically appropriate points of wear. Meow.
Stir vigorously turns suspension dark blue. Next wait for the indigotin to settle to the bottom and then remove the 50 gallons of water in top of that layer. Simple!
