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Ansco 216 Chrome Alum Photographic Hardening Bath

FormulasThis bath may be used in place of the regular acetic acid short-stop to give additional hardening to film. It is particularly desirable in hot weather, for tropical development, and for negatives which have to be enlarged while wet.


Potassium Chrome Alum 30 g
Water 1 L


Films should be agitated throughly wien immersed in the solution. Maximum hardening will be obtained with about three minutes treatment.


The solution should be used fresh as it does not keep well. Formation of a greenish sludge is an indication that the solution should be replaced by a fresh bath.


If the chrome alum used is such that sludge is formed when the bath is first used and addition of condcentrated sulfuric acid (2 ml per liter or 1/2 dram per 32 ounces) can be made to the solution to overcome this condition.


From Ansco Formulas for Black and White Film by GAF, 1948 – Formulas are provided for historical reference. They may not work well with modern films and papers. Some of the chemicals can be dangerous. As with all photographic processes, be careful.