Alkali fixers

Alkali fixers, especially those compounded with ammonium thiosulfate, are the most efficient and effective with modern emulsions in both film and paper. Although they have been used for scientific purposes since at least the 1930s, they have only recently become commercially available. Photographers Formulary TF-4 is the first to be widely distributed. The formula forTF-3, a fixer having similar properties but a shorter shelf life, is given in the Formulas section. 

No hypo clearing agent (HCA) is required when using alkali fixer. 

No acid stop bath is required when using alkali fixer. In order to preserve the alkalinity of the fixer, acid stop bath should not be used. 

The opposite is also true. If you take a print (or negative) from an alkali developer and place it directly into an acid fixer, the fixer will rapidly become neutral in pH and no longer work. This is perhaps more serious than going the other way because all the prints and negatives that appear to be fixed while the acid fixer is becoming less active due to alkali contamination, will deteriorate in a relatively short time after processing. 

One reason phosphates have been little used is that they can cause a scum if the film is plunged directly into a fixer that contains alum hardeners. Since the use of alum hardeners is waning, this may no longer be a major concern. In powder form, the phosphates appear to be less stable than other alkalis. 

Uses An alkali used as a substitute for caustic and carbonate alkali in negative development. Used as a water softener. Good for cleaning and detoxifying vessels and trays that contained fixer. 

Most fixers have strong odors caused by sulfur dioxide. The substitution of balanced alkali for boric acid in the F-6 formula eliminates the odor almost entirely. 

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