Question

Which of the following is the characteristic property of a vat dye

• A. must be reduced to a soluble form so that it can dissolve in the dye bath and get Be trapped in the cellulose fiber.
• B. penetrates both the outer ring and the inner core of a piece of fiber.
• C. Remains in its soluble form inside the denim fabric.
• D. Must be in an insoluble form so that it can get trapped in the cellulose fiber.

Answer 1

Answer: (D)

Must be in an insoluble form so that it can get trapped in the cellulose fiber.

Vat dyes are essentially insoluble in water and incapable of dyeing fibers
directly. However, reduction in alkaline liquor produces the water-soluble
alkali metal salt of the dye, which, in this leuco form, has an affinity for
the textile fiber. Subsequent oxidation reforms the original insoluble dye. The
color of denim is due to indigo, the original vat dye
So a vat dye must be reduced to a soluble form so that it can dissolve in the dye bath and get trapped in the cellulose fiber.
Hence option D is correct