Basic dyes are
salts of the colored organic bases containing amino and imino groups and also
combined with a colorless acid, such as hydrochloric or sulfuric. They are
brilliant and most fluorescent among all synthetic dyes but have poor light and
wash fastness. Cotton dye having higher fastness properties replaces in dyeing
cotton for them. Basic dyes are cationic which has positive electrical charge
and are used for anionic fabrics which are negative-charge-bearing, such as
wool, silk, nylon, and acrylics where bright dying is the prime
consideration.
Auramine O is a yellow fluorescent dye; very soluble in water, soluble in
ethanol; used to stain acid-fast bacteria in sputum or in paraffin sections of
infected tissue and as a component of the Truant auramine-rhodamine stain for
tubercle bacilli; used as an antiseptic agent.