Fixing solution

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.