sentences: )Surface cleaning
  may be used as an independent cleaning technique, as one step (usually the
  first) in a more comprehensive treatment, or as a prelude to further treatments
  (e.g., aqueous immersion) which may cause dirt to set irreversibly in paper
  fibers.The purpose of surface cleaning is to reduce the potential for damage to paper
  artifacts by removing foreign material which can be abrasive, acidic,
  hygroscopic, or degradative.