Greying, which is usually caused by the re-deposition of particulate soil, continues to be a common problem in the drycleaning industry.

Dirty solvent coming into contact with garments is the fundamental cause of greying.

Complaints such as “It’s not as bright as it was” can be traced to either poor classification or a process structure that involves cleaning whites in baths of distilled solvent without filtration. To reduce the risk of re-deposition, particulate soiling must be removed quickly from the vicinity of the garments during the cleaning cycle.The first stage of the process should be a wash from the working tank over the filter. The filter wash is followed by a rinse in distilled solvent.

However, even the most effective process structure will result in small but measurable amounts of re-deposition on white loads. These small amounts of re-deposited particulates will tend to build up over several cleaning cycles until discolouration becomes noticeable.

It is critical that for the first stage of the process the filter is producing crystal clear solvent at a good flow rate, before filtered solvent is introduced into the cage. The following process is suitable for cleaning robust white loads in perc:

• 6min filter wash, low dip using base tank solvent (solvent must be no more than a very light straw colour)

• drain, followed by short extract to still

• 2–3min rinse in distilled solvent, drain and final extract to base tank

• dry at a maximum outlet air temperature of 60C.

The above process structure will need to be adjusted for sensitive white loads.