pH

The pH of a water extract of scoured wool is frequently required. pH is a measure of the acidity or alkalinity of the wool. The full range of pH values runs from 0 to 14, with 0 being extremely acidic, 7 being neutral and 14 being extremely alkaline. The pH scale is logarithmic away from neutral, and small changes in the values towards the acid or alkaline end of the scale represent considerable differences in processing conditions. However, public supply water may have a pH anywhere between 5 and 9, which is where the scale is most sensitive.

Most scours produce wools in the range 3 to 10. The mean values for pH between 5 and 9 can have a large standard deviation simply because of the extreme sensitivity of the scale in this region.

The pH of the wool is often specified by dyers, since dying has to be carried out at a specific pH level. Whilst the pH can be easily altered by the addition of chemicals to the dyebath, having the correct pH to start with saves the dyer money.

The appropriate test method is IWTO-2, which is very detailed in order to minimise the variability of results. Nevertheless, the maximum probable difference between two separate determinations of the pH of a water extract using this method is 1 unit.

There are no sampling regulations for this test and it is hence not certifiable under IWTO auspices (for an explanation of this term, refer to Trading certification services).