I tried to build one in high school, but it did not work :( I think the school had a hand powered high voltage generator with some kind of leather band I took

I tried to build one in high school, but it did not work :( I think the school had a hand powered high voltage generator with some kind of leather band I took it to university and gave it to a professor who might have a more stable HV power supply. I got it back after a year, and they said it was too dangerous to try it out, or something