Fixing solution

Last revised by Dr Jeremy Jones on 19 Sep 2021

Fixing solution is used in the darkroom to fix (i.e. remove unexposed silver) the developed and rinsed x-ray film in conventional radiography.

  • fixing agent: sodium/ammonium thiosulfate, dissolves unexposed silver
  • hardener: potassium alum, to harden the gelatin emulsion in film
  • acidifier: sulfuric/acetic acid, to remove any residual alkalinity from previous developing

After fixing, washing under running water is done, which is then followed by drying of the x-ray film.

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