Tape Bakery?

In the mid 1970s, the tape manufacturers changed the formula for the binder used to glue the rust (ferric oxide) to the plastic (mylar). Little did they know that over a period of time the binder would take on moisture and cause the rust to leave the plastic.
If tapes are handled carefully and heated in a controlled oven (not the one in your kitchen) at a prescribed temperature for a prescribed period of time, the tapes can be made playable for a short period of time.