Bright but not always best

When fabric changes colour or fades during use, the problem is not always what it appears to be. What seems to be a change in colour may be merely an optical effect created by an optical brightening agent, commonly known as an OBA or fluorescing agent.

OBAs are dyes which react to UV light and convert it to visible spectrum, effectively fluorescing and making the fabric appear brighter and whiter. They are widely used – in fabrics, paper, plastics, paints, detergents – and where their use is controlled, they enhance the visual appearance of the product. The required ‘whiteness’ of sheets, pillowcases and table napery is usually created by the application of OBA during the manufacturing and preparation of fabrics prior to make-up and sale.

However, OBAs may well be a component of the launderer’s preferred detergent and this can create difficulties in the processing of coloured work as the progressive use creates an apparent colour change, very similar to the gradual loss of colour caused by the removal of the base dyestuff.

Masking effect

This usually leads to the customer blaming the launderer for spoiling or damag- ing the fabric by using a bleach, or by washing at too high a temperature, where in fact, the cause is a detergent containing an optical brightener. The overlay of OBA on the fabric effectively ‘masks’ the base colour, and in the presence of UV light, the reflected colour seen is a combination of the original or base colour plus the visible spectrum transmitted from the OBA on the fabric surface.

In this situation, it is often possible to restore the fabric to its original colour or hue by the careful use of a specific product known as an OBA quencher. This ‘masks’ the OBA and prevents the conversion of UV to visible spectrum light, allowing only the base colour to be seen, and often restoring the original colour or hue.

Turning grey

Like many dyestuffs, OBA can progressively be removed in laundering processes, and, in recent years,there have been cases where the required or expected ‘whiteness’ has been seen to diminish over time, leaving the fabric looking grey or off-white. This has been seen with towelling and napery and again usually lays the launderer open to complaints that the work is not being washed properly.

What has actually happened is that the wash process has removed the OBA, and the fabric is no longer able to reflect or re-transmit the UV light as part of the visible spectrum and so the work looks less bright.

Clean but not white

There have been instances of a launderer being threatened with litigation by a customer, on the grounds that “the laundry has ruined the hotel’s stock of white towels by bad processing, turning them grey and generally making them unacceptable for use in a high quality hotel.” However, on investigation, it was found that the towelling fabric had lost the original OBA, because it was fugitive, and the ‘grey’ colour was the base textile colour. The work was perfectly and hygienically clean, but not of a ‘whiteness’ expected by the customer.

In this specific instance, the problem was a manufacturing one and outside the control of the launderer, but the judicious application and use of an OBA soon restored the towels to their former white appearance.

On the basis that OBA is a dyestuff and will gradually be removed, by washing, or bleaching treatments, the launderer will normally be required to use a detergent formulation for processing whitework which will incorporate an OBA component. So any OBA lost during washing will be replaced, hopefully maintaining a level which will keep the fabric looking as bright and as white as the customer wants.

Too much

However, the opposite of this situation can also occur and too much OBA can have an adverse affect, even on whitework. In this case, the fabric displays colour changes which can vary in shade and intensity to a remarkable degree.

A recent example was a child’s white 100% polyester dress which had been washed in a proprietary household detergent and had turned a delicate shade of lilac and mauve. The colour intensity was greater where there were several layers of fabric, such as on the hems, seams, and gathers.

Here, a build-up of OBA had increased the intensity of reflected light.

In this situation, it may be possible to remove the excess OBA, either by using a specific quenching treatments or by the careful and appropriate application of a bleach treatment.

The effects of an OBA build-up can be much worse in the case of coloured work. For example, in uniforms with a corporate colour scheme, any degradation would be unacceptable as it could be seen as spoiling the company image.

Technicolour effect

Similarly, the hotel and hospitality industry makes great efforts to maintain a high level of presentation and the visual impact of a well-laid-out dining room, banqueting or conference facility could be marred if the table linen, supposedly matching, in reality showed as many variations and hues as Joseph’s Technicolour Dream Coat! While this may be a slight exaggeration, the problem is none-the-less real. Customers may not send their total stock to the laundry on each and every occasion, so there can be no control or indication as to how many times an individual item has been processed. Where the launderer is using a detergent containing an OBA, for coloured fabrics, there will be a progressive build up. As a result, the colour will appear to have faded and the textile manufacturer or supplier will usually be blamed.

In general, professional launderers and their detergent suppliers will work together to ensure that the detergents are formulated to meet specific requirements and provide optimum conditions for achieving both cleanliness and a good appearance If one of the launderers’ aims is to maintain the whiteness and brightness of white or coloured work, they should remember that while OBAs will do this, they can create apparent changes. Simply put, where possible avoid using detergent formulations containing OBA when processing coloured work.

Commercial laundries are usually fully aware of the problems associated with OBAs, but the problems are not always recognised in smaller operations or , particularly where laundering is not the core business. Detergent companies and textile suppliers can often be a valuable source of advice, guidance and support here. Where there is a problem, they may be able to suggest methods of dealing with it, so avoiding possible conflict and misunderstanding.