1.1. Dyes and coloring materials
Highly colored substances, widely known as colorants, can be
used to impart color to an infinite variety of materials described
technically as substrates. Colorants can be subdivided into dyes
and dyeing is a common application used for coloring fibrous substances
and termed as staining in the case of biological materials.
The dye is generally applied in an aqueous solution, andmay require
a mordant to improve the fastness of the dye on the fibre.
Synthetic dyes quickly replaced the traditional natural dyes and
being used widely in textile, food and leather dyeing. Azo dyes
are synthetic organic colorants, characterized by chromophoric azo
groups (–N N–) prepared by generally known unit process of Diazotization
and coupling reaction. However, whereas azo dyes are
relatively resistant to degradation under aerobic conditions, they
can be readily reduced to form aromatic amines under anaerobic
conditions. Various health problems associated with azo dyes are
well reported