Once I was doing an experiment on capacitors, I discharged a capacitor totally(I mean 99.999% coz theoretically we can't totally discharge a capacitor) and checked by a microammeter, the reading was zero. Then I put the capacitor on a bench (insulator), after a while, I connected the capacitor with a microammeter and the pointer of the microammeter jumped to 0.5mA! I repeated it several times and same result could be obtained. Now I am wondering where do the charges come from, from the bench? Could someone explain it please.