Positive? or Negative charge? How to tell on a Van de Graaff generator?

[space-time]

Do you have a multimeter to connect to it, I would set it up to measure current, and turn it on, there should not be much charge accumulated but you might measure a few microamps. If that does not work, use it as a voltmeter, although depending on how large the impedance of the DMM is, the voltage can get high and I am not sure if it will damage it or not. I would stick with Ammeter first

do you have some capacitors? some diodes?