Tropical hardening bath for films and plates, for use after development, at temperatures from 24°C to 35°C.

Is recommended to be used in conjunction with Kodak Tropical Developer DK15.

Mix chemicals in order.
Chromium(III) potassium sulfate (chrome alum)
Sodium sulfate desiccated
Water to make

If crystalline sodium sulfate is preferred instead of desiccated sulfate, use 140 grams.

Agitate negatives for 30–45 seconds when they are first immersed, to avoid unevenness, and leave them for 3 minutes. After the equivalent of 20 10×8″ films per 4.7 liters been treated, the bath should be replaced, otherwise scum markings will result.

The freshly-made bath is violet-blue colour and keeps indefinitely while unused. A partially used bath deteriorates on standing for a few days, the colour changing to a yellow-green. The hardening bath should never be overworked.