Colourants are the materials that are employed in different sectors for coloring different materials. They are broadly classified as pigments and dyes.
What are Pigments?
Pigments
are the solid materials available as the tiny discrete particles which are
insoluble in the materials they are dispersed in. They can be both organic or
inorganic, black or white materials. As they are suspended in the binder the
physical condition of the particles is of extreme importance. This is the
ultimate reason why manufacturers focus on control production conditions to
ensure uniformity within each production. The main reason behind this is the
drastic effect that can occur even due to the small changes in the shade and
strength of the pigment.
What are Dyes?
These
are also the colored substances that are dissolved in solutions or substrates
giving them a colored appearance, they are mainly soluble in water. As they
dissolve in water they lose their crystal-like structure.
Both
pigments and dyes are used for the same purposes but they differ in their
chemical, physical properties and also in the processes utilized for applying
them on materials.
Lightfastness
The
relation between the chemical constitution and lightfastness of pigments is
still not clear but it is also considered as part of the chemistry of the
molecule.
Dyes
are the most susceptible to the ultraviolet rays originating from the sun as
they tend to break the bonds of dye molecules and destroy the colors making the
color on fabrics appear faded and worn away.
Most of
the pigments in today's time hold lightfastness properties except few pigments.
