What if I use existing magnetic paper from tickets?
Prototype 2.
Doesn't work either.
No matter what they use for magnetic paper, it's not good.
Prototype 3:
Iron grains were too big. Let's use fine iron powder!
Result: the tape is very heavy and responds to magnets a lot, but it doesn't work with the tape recorder.
Hypothesis: it needs both magnetic and paramagnetic material in the tape. Is it too magnetic?
