>breakdown voltage castor oil
They used 20kV in the experiment above, supposedly at room temperature, below what's been found in (pic).
https://www.ijser.in/archives/v2i4/SjIwMTMyMjk=.pdf
If castor oil would have acted as a conductor at that voltage, current would just flow from therough the oil to the ring, and there'd be no need for the ball bearings to form the structures.