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  1. Decolorization of coloured materials. The two
  2. main types of bleaching agent are the
  3. oxidizing bleaches, which add oxygen and
  4. remove hydrogen, and include the ultraviolet
  5. rays in sunshine, hydrogen peroxide, and
  6. chlorine in household bleaches, and the
  7. reducing bleaches, which add hydrogen or
  8. remove oxygen, for example sulphur dioxide.
  9. Bleaching processes have been known from
  10. antiquity, mainly those acting through
  11. sunlight. Both natural and synthetic pigments
  12. usually possess highly complex molecules, the
  13. colour property often being due only to a
  14. part of the molecule. Bleaches usually attack
  15. only that small part, giving another
  16. substance similar in chemical structure but
  17. colourless.
  18.