Kodalith, unless subjected to high temperature and humidity, will last a very long time. I have made negatives from 35mm color slides on it but one must remember that Kodalith is an extreme contrast film, not intended for pictorial use. Little or no gray tones. It is possible to get a continuous tone negative out of it using highly dilute D-76 (1:9) or Technidol. Chances are it will still be rather high contrast, though. Kodalith is fun stuff to experiment with. Expose it at ISO 6 or, under the enlarger, at paper speed. Try it. Play with it and have some fun.