vat dyes
Dyestuffs that are insoluble in water, but the
"leuco" compounds of which, subsequent to
reduction, are soluble in dilute alkalies. In this
state vat dyes have a great affinity for
cellulosic fibers, e.g., cloth, paper, etc. After
being impregnated with the reduced dye, the
material is then exposed to the oxygen of the air,
which causes re-oxidation of the leuco compound
back to the insoluble state. Vat dyes are among
the fastest dyes known, and, despite the
development of new classes of fast dyestuffs, they
continue to be used where high standards of color
stability are required. (17 , 235 )
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