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Here is a riddle: Found old rolls of film among grandpas things. They are tightly wrapped in tin foil. Back in the day in Russia (where he was from) there were no disposable film canisters, all canisters had twist-off bottoms and were reloaded with film. So... I have no way of knowing if this foil-wrapped film is exposed or unexposed. If its exposed, will it get ruined if I put it through another round of development? Is there any safe way to open it to see if it already has pictures? How do I tell if there is anything on it without ruining it if it hasn't been exposed? Many thanks in advance!