Fading

Fading is the result of some change in the structure of the dye molecule due to absorption of light, reaction with air pollutants, laundering, dry cleaning and/or other agent. 

Fastness to sunlight: Fading in sunlight is due to ultraviolet radiation which initiates chemical degradation of the dye molecule through the loosely held electrons of the chromophores. 

Wash-fastness: The loss of colour will occur during laundering if dyes have been used which are held loosely by the fibre.

Dry-cleaning-fastness: The loss of colour during dry-cleaning is referred to as a lack of dry-cleaning-fastness.

Fastness to perspiration: Perspiration is a complex combination of body oils, fats and saline solution. Perspiration may result in a loss of colour.

Fastness to compounds and bleaches containing chlorine: Chlorine-containing compounds are used for killing bacteria in swimming pools. This means that swimwear and towels have to withstand the oxidation effect of chlorine-containing compounds. The chemical degradation of dyes sensitive to both these reagents is due to their oxidizing effect.

Fastness to sea water: Fading from sea water is due to sunlight and should be referred to as fading due to sea water and sunlight. This hydrolytic reaction produces hydrochloric acid which degrades the dye molecules.

Fading due to other causes: Fading can also be caused by inorganic acids, alkalis, fruit juices, etc. Fading due to dry ironing and steam pressing is the result of degradation of the dye molecules.