Better color strength results are dependent
on the metal salt used (Kamel et al., 2009). Strong
co-ordination tendency of Fe enhances the
interaction between the fiber and the dye, resulting
in high dye uptake (Jothi, 2008). Ferrous sulphate
and Copper sulphate have the ability of forming coordination
complexes (Co-ordination numbers are 6
and 4 respectively). Functional groups such as amino
and carboxylic acid on the fiber can occupy the
unoccupied sites on interaction with the fiber. Thus,
a ternary complex is formed by the metal salt on
which one site is with the fiber and the other site is
with the dye.