vat dye

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A dye, such as indigo, that produces a fast color by impregnating fiber with a reduced soluble form that is then oxidized to an insoluble form.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of a type of dye, many based on indigo, in which a soluble form is used to impregnate a fibre or fabric and is then converted to an insoluble form

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a water-insoluble dye that is applied by reducing the dye to an alkaline form, applying the dye, then regenerating the insoluble dye by oxidation in the material; used for dyeing cotton