Ilford IF-15 Potassium Alum Acid Hardener-Fixer

This hardening fixer is intended for use with films and plates.

Sodium thiosulphate (hypo), cryst . . . 320g
Sodium Silphite, anhyd . . . 30g
Boric Acid, cryst . . . 10g
Acetic Acid, glacial . . . 18cc
Potassium Alum, cryst . . . 25g
Water to make . . . 1 litre

Dissolve the hypo in 500cc of hot (52C or 125F) water. Upon cooling, add the sulphite.

Dissolve the boric acid, acetic acid and alum in 150cc of hot (52C or 125F) water. Allow this to cool to below 20C (68F).

Now slowly pour the acid-alum solution into the hypo-sulphite solution and add enough water to attain a total volume of one litre.

To obtain full hardening, films should be allowed to remain in the bath from 5-10 minutes.