If you are talking about powder coating, it is not very effective with nonconductive materials because they don't get electrostatic charge as well as metals. However it is still possible to powder coat glass and ceramics by hot flocking. It is heating the item first in the oven then spraying the paint powder which melts upon contact to the material and thus bond even without electrostatic charge.
I would usually set to 4 volts and max to about 6 volts. More than that and I experienced the transistor on the high voltage generator overheating also the secondary on the transformer arcing until destruction. Yes, I tried to adjust the voltage in an attempt to mitigate faraday cage effect on some items. I have new updated high voltage generator and new gun version vids to be uploaded soon. Please check those out.
