Vat dyes, Mordant dyes

Vat Dyes

Vat dyes are insoluble in water and cannot be used directly for dyeing. But on reduction to a leuco form (colour less), they become soluble in an alkali and acquire affinity for cellulose fibres. A solution of the leuco form can be applied for dyeing or printing. On oxidation the original insoluble dye is formed within th structure of the fibre. Indigo and indigosol O are dyes which belong to this class.

Mordant Dyes

Mordant dyes are primarily used for dyeing of wool in the presence of metal ions. The metal ion binds to the fabric and the dye acting as ligand co-ordinates to the metal ion. The same dye in the presence of different metal ions imparts different colours to the fabrics. The colours imparted by Alizarin in presence of different ions are given below

Ions and colours

Al3+ = Rose red

Ba 2+ = Blue

Cr 3- = Brownish red

Mg 2+ = Violet

Sr 2+ = Red

For details about Dyes visit http://entrancechemistry.blogspot.com/2012/08/chemicals-in-every-day-life-dyes.html