vat dye

noun Chemistry.

1. any of the class of insoluble dyes impregnated into textile fibers by reduction into soluble leuco bases that regenerate the insoluble dye on oxidation.

noun

1. a dye, such as indigo, that is applied by first reducing it to its leuco base, which is soluble in alkali, and then regenerating the insoluble dye by oxidation in the fibres of the material