Oxidation and bleaching

In detail

A stain is visible because the molecules in it contain a chromophore: a structural feature, usually a system of alternating double bonds, that absorbs some wavelengths of light and reflects others. Oxidising bleaches attack that structure. When the chromophore is broken, the molecule stops absorbing visible light and the stain stops being visible, even though the molecule itself is still present on the fabric. This explains behaviour that is otherwise puzzling. Bleaching is not removal, so a bleached stain can sometimes reappear if the residue is later altered. It is not selective either: a chromophore in a fabric dye is chemically no different from a chromophore in a wine stain, which is why chlorine bleach strips colour from garments as readily as it removes marks from them. The difference between chlorine and oxygen bleaches is one of strength and of what else they do — hypochlorite is the more aggressive oxidant and also attacks protein fibres, while peroxide-based bleaches are milder and generally spare fabric dyes.

Why

• Sodium hypochlorite (chlorine bleach) is explained by Oxidation and bleaching
• Sodium percarbonate (oxygen bleach) is explained by Oxidation and bleaching
• Hydrogen peroxide is explained by Oxidation and bleaching
• Hydrogen peroxide is explained by Oxidation and bleaching

  Sprint 9 re-points this at a regulator sheet that was read, alongside the existing background chemistry.

• Cotton is explained by Oxidation and bleaching

  Quantified rather than asserted. Ten chlorine washes did more damage to the cellulose than one hundred ordinary ones.