Jean-David Beyer wrote:
I forgot: the film came in metal cans with a screw-cap on them, with a trace
of rubber-like compound where the cap touched the top of the can.

You forgot the most important part. You could open the cassettes by banging
them on a table, and then re-use them.

Geoff.

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Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM