Dyestuffs and other coloured materials
DOI link for Dyestuffs and other coloured materials
Dyestuffs and other coloured materials book
An auxochrome was conceived of as a group which, while not giving rise to colour itself, caused a 'deepening' of colour (i.e. a lengthening of wavelength) when introduced into the structure of an already coloured compound. Amino and hydroxyl groups could be thought of as being of this kind. The distinction is not really so simple and absolute as this would seem to suggest: all the groups contribute to the spectrum of a compound on an equal basis though some have a greater, others a lesser effect.