Scouring, is a chemical washing process carried out on cotton
fabric to remove natural wax and non-fibrous impurities (eg the
remains of seed fragments) from the fibres and any added soiling
or dirt. If the appropriate reagents are used, scouring will
also remove size from the fabric although desizing often
precedes scouring and is considered to be a separate process
known as fabric preparation. Preparation and scouring are
prerequisites to most of the other finishing processes. At this
stage even the most naturally white cotton fibres are yellowish,
and bleaching, the next process, is required. Bleaching improves
whiteness by removing natural colouration and remaining trace
impurities from the cotton; the degree of bleaching necessary is
determined by the required whiteness and absorbency. If the
fabric is to be dyed a deep shade, then lower levels of
bleaching are acceptable, for example. However, for white bed
sheetings and medical applications, the highest levels of
whiteness and absorbency are essential.