I need to make a hardening fixer for using with liquid light and was thinking of Kodak F6. Formula says to use "potassium alum". I've got an old kodak glass bottle labeled "potassium chrome alum" [purple crystals inside] and was wondering if anyone knew if this was the same as the "potassium alum" in the Kodak F6 formula? Alternatively, does anyone know a good non-rapid hardening fixer to use with liquid light? Thanks.