community of dyers

Indigo can't be set with a fixative, since it is a vat dye. Instead, what you do is make a relatively weak solution of indigo, which requires reducing it first with strong chemicals, since the oxidized form is not soluble in water. You dip the fiber into the reduced indigo vat, allowing some of the yellow reduced indigo to penetrate inside the fibers, and then you pull it out of the dyebath, allowing the yellow indigo molecules to be oxidized by the air into the insoluble blue form. Then you repeat this procedure until the desired degree of color intensity is reached. The insoluble indigo dye molecules are thus fixed in place inside the fibers, where they will not rub off or wash out.

If you try to take a shortcut by using one dip, in an overly strong solution of reduced indigo, then too much of the indigo stays outside the fiber. When the indigo molecules that are outside the fiber are oxidized, they are left on the outside of the fiber. This means that there is nothing holding them on to the fiber. Oxidized blue indigo on the outside of the fiber will rub off, even when dry. It's a grave manufacturing defect. Never sell indigo-dyed fabric that has been dyed the wrong way!

Unlike fiber reactive dyes, acid dyes, and direct dyes, positively-charged fixatives such as Retayne are not attracted to the dye molecules, and do not work to fix them in place. Retayne does not work on indigo.

The indigo dye vat is very alkaline, that is, it has a high pH. It is important, for the sake of the fiber, to neutralize the pH by rinsing well, and some dyers like to neutralize the alkalinity by rinsing in vinegar. However, vinegar is not a fixative for badly unfixed indigo. You cannot use vinegar to fix in place indigo molecules that have carelessly been applied only to the outside of the fiber. Jill Goodwin, in her book A Dyer's Manual (avoid the first edition in favor of the second), recommends rinsing in soft water containing two tablespoons of salt and two tablespoons of vinegar (presumably per gallon), which she says, for properly applied indigo on wool, will reduce the tendency to bleed.

Of course you must wash your indigo-dyed textiles to remove any dye that is still on the outside of the fibers. There will inevitably be some. Jim Liles, who includes a number of extremely detailed recipes for dyeing with indigo in his book The Art and Craft of Natural Dyeing, advises washing out this oxidized indigo with any good modern detergent that lacks whiteners and brighteners; he recommends Ivory Liquid or Tide. He says that cellulosic materials such as cotton should be soaked for several hours before being dried and used, and that rinsing with an acid such as vinegar is essential for protein-containing fibers, though not for cellulose. He says that he uses the acid rinse even when it is not necessary, though, using one to two fluid ounces of vinegar (two to four tablespoons) per gallon of rinse water (that's 30 to 60 ml per four liters).

I get a lot of mail from non-dyers who want to know how to fix indigo that has been applied incorrectly, sometimes on blue jeans, and often on textiles purchased in the tourist trade in Guatemala or Vietnam, more rarely Africa. I advise the buyers of commercial clothing to return it for a refund if several washings does not stop the crocking problem. Of course the makers of the tourist-trade indigo in foreign countries don't have to worry that their goods will be returned if they have been manufactured incorrectly.

-Paula