Optical Brightening Agents, also called Fluroresvent Whitening Agents, are usually abbreviated to OBA or FWA when you see them in the list of ingredients on the side of detergent containers – both domestic and commercial. Sometimes their presence is disguised with other wording.
An OBA is designed to attach itself to the surface of the fabric (they tend to be more attracted to natural fibres such as cotton and linen than they are to synthetic ones) and react with the ultra-violet portion of normal sunlight.
The OBA absorbs ultra-violet light which is invisible to the human eye and re-emits it as intense white light which is very visible.
The effect is to enhance the brightness and liveliness of white fabrics making an OBA an essential ingredient when washing white bedlinen and white polyester-cotton coats for example.
However; diluting the light from a coloured fabric with white light makes it look pale and faded and the effect gets worse and worse with multiple laundering. This is because OBA builds up progressively onto the fabric surface so that the apparent fading gets worse month by month, even though the dyes themselves might not be affected. You can demonstrate all this using a simple and inexpensive bank note detector (available from RS Components from about £15). Under ultra-violet light the problem will look much worse than it does in ordinary daylight which confirms this particular fault.
There are plenty of detergents available which do not contain an OBA and these should always be specified for coloured work and coloured prints. One can expect that over half of the problems with fading of coloured prints can be attributed to OBA and not to the effects of laundering.
Colin Farquharson, St Ermin’s Hotel
Suzy Brandwood, The Elms School
Wendy Clayton, Chepstow Nursing & Care Home
Fr Oliver, Douai Abbey
James Suter, The Gliffae Country House Hotel
Shaid Aziz, Bright Wash Launderette
Marilyn Collins, Oaklands Care Home