The dyes which have no affinity towards textile fibres and
are attached with the fibre with the help of mordants are known as mordant
dyes.
Mordant dyes may be organic or inorganic substances. The
most commonly used mordant is inorganic chromium. So sometimes these dyes are
called chrome dyes.
These dye molecules have some mordant attracting groups
which have some influence on secondary valency bonds due to a particular
configuration with metal ions so that insoluble color takes are produced.
Mainly neighbouring –OH groups or –COOH groups appear in neighbouring position
in azo dyes. A metal equivalent takes the place of hydrogen in the –OH group
or -COOH group each time.
The mordants have affinity both for fibre and dye. So those
dyes which do not have any affinity to fibres can be applied by using a
suitable mordant ( as dyes have mordant attracting groups)