FIXING BATH |
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| by Ted Peterson |
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| Most fixing baths contains sodium thiosulfate (hypo) which dissolves the undeveloped silver halides. Acetic acid bath is used to set the ph correctly before the fixing bath and to help the hardening action. |
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| Potassium alum is the hardening agent used in most fixer to harden the gelatine of the emulsion in order to prevent excessive swelling of the paper or film in the water wash. Boric acid can be added also to increase the hardening of the alum and helps prevent aluminum sulfite sludge which is formed if the stop bath does not neutralize the alkalinity of the developer carried over. |
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| Most of the time the fixing bath is overworked far beyone its capacity. Two fixing baths in succession are superior in every way to one fixing bath. |
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| When a new fixing bath is mixed, place a small piece of film in the fixer and note the time required to clear the film. Each day place another piece of film into the same fixer and check the time to clear the film. When the time doubles then you should dump the fixer and start over. |
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| A test for worn out fixer can be made by; 10 grains of Potassium Iodide in 3 oz. water. Put a few drops in about 1 oz of fixer. If it causes a cloudiness which persists it indicates that the fixer should be replaced. |
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| Following the fixer the print should be washed in several changes of water and then placed in Hypo Eliminator (one tablespoon of Sodium Carbonate per gallon of water) makes an effective hypo eliminator. |
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