Indigo was the dye that turned me from a casual user into an addict. Indigo is magic: submerge any porous natural substance in the less-than-pleasant-smelling-frog-pond-greeny-yellow vat*, soak for a few minutes, remove from the vat and watch the material change from yellow, to green, through teal to blue in less than a minute. MAGIC! (It’s actually simple chemistry, but I’ll get to that later.)
I first saw an indigo vat in use at a linen processing workshop in Rhode Island in 1998 and fell in love. Within a week I had my own vat. While I was deliriously dyeing one evening my friend Hannah stopped by. After I assaulted her with my excitement and demonstrated the dipping and dyeing. She looked at my bedraggled dye-covered self and asked “Where are your car keys?”
“Um, on my desk. Why?”
“I’m going to get us some pizza, because you’ll stay here all night and starve if I don’t.”
She was right. Each dip in the vat yielded the same excitement as the first, I was hooked.
Indigo is a plant based pigment derived the leaves of plants. Are there blue plants? Not unless we’re on Planet Seuss.
Much of the world has native plants that produce indigo and more than fifty different species of plants produce indigo in usable quantities. Indigo-bearing plants come from families as diverse as the bean family (leguminosae), cabbage family (cruciferae) and rhubarb family (polygonaceae). Examples of indigo-bearing plants include several species of Indigofera, Japanese Indigo (Persicaria tinctoria and Polygonum tinctorum), woad (Isatis tinctoria), dyer’s oleander (Wrightia), Strobilanthes and Marsdenia.
These plants contain “indigo precursors” instead of the actual pigment. They contain the glucoside indican which is extracted from the leaf through fermentation. Indican breaks down into glucose and indoxyl. Indoxyl is colorless until it undergoes oxidation (through aeration of the fermentation pool) to yield indigotin in the form of a blue, insoluble sludge which is dried and sold in squares before being ground into powder. (Sorry about the chemistry speak, I’m an artist raised by scientists.) Marco Polo accurately described this process in during his travels through India in the late 13th century.)
In order to be an effective, permanent dye the indigo pigment must be turned into a yellow substance known as leuco-indigo or indigo white. This dye bath is called a vat.
Blue indigo is dissolved in an alkaline solution (usually created with lye from wood ash) and then reduced (all extra oxygen is removed from the vat liquid and some of the H2O molecules break down). This yields a dye which will penetrate fibers and create a permanent dye after exposure to the oxygen in the air.
I had some fits and starts with vat creation and accurate, permanent dyeing including turning my boss blue when I dyed a dress for her. I’ve now been dyeing with indigo for 18 years and create beautifully dyed yarns, clothing and indigo shibori textiles - but that’s another story.