Hence, they enter the fiber and for

Hence, they enter the fiber and form
ionic bonding between dye and fiber and metal and fiber and
finally with dye and metal ions. The dye-metal chellates thus
produced also form coordinate bonds with the uncharged
amine (–NH
2)groups of silk. Again,one molecule of dye can
form a bond with one site of fiber molecule. But one molecule
of mordant can form bonds with two or more molecules of
dyes. As a result, when the mordant molecule binds on to
fiber it holds two molecules of dye with it. Therefore, using
mordant, the color yield was increased.
It is known that some transition metal ions can bond
strongly with natural dye molecules due to their ability to
form coordination complexes and thus produce deep color
on the fabric. Iron salts such as ferrous sulphate as transition
metal mordant form a large number of complexes with
Table 2: Color yield, color coordinates, and color difference of the dyed fabrics.
Figure 3: Possible structures of pelargonidin with FeSO4 on silk.
the dye molecules, mostly octahedral ones with coordination
number 6. As a result, some coordination sites remain
unoccupied when they interact with the fiber and at that time
functional groups such as amino and carboxylic groups on
thesilkfibercanoccupytheseunoccupiedsites.Thus,ferrous
sulphate salts can form a ternary complex on one site with
the fiber and in the other site with the dye. This resulted in
higher dye uptake as well as shade change due to mordanting
with ferrous sulphate. On the other hand, aluminium and tin
salts formed weak coordination complexes with the dye. This
tends to form quite strong bonds with the dye molecule but
notwiththefiber.Thus,theyblockthedyeandreduceits
interaction with the fiber. This is the reason behind the lower