Generally protein fibres are not dyes with azoic dyes,
because in naphtholation process a large amount of alkali is used in bath. But
protein fibres are weak to alkali. So the alkali of naphtholation bath may
degrade fibres. Again naphtholation protein fibres take part in coupling
reaction with amino group. So they can not take part in coupling reaction with
diazo component again. For these reason protein fibres(silk, wool) are not dyed
with azoic colors.
