Electronic – Determining voltage by arc length

Short for "Corona Dope," also found as high dielectric strength insulating paint. Corona dope is still sold by the usual electronics chem suppliers. I find that crazy glue cyanoacrylate works fine. But note that these painted-on coatings are intended to stop HV leakage across a surface. If you have sparks leaping across an air gap, then instead you need a thick material rather than paint.

Silicone caulk works fairly well, but use the ammonia-stink RTV type, not the water-base stuff found in paint stores.

Also note that arcing usually causes and is caused by a carbonized surface path. Make sure to first scrape away any (possibly invisible) damaged insulating surface which has become conductive.

In an electric arc, electrons are being stripped from their atoms in the air & fired with high energy towards the anode.

Some of the electrons are fired from the cathode directly, and others are stripped from air atoms, but eventually, if the plasma is sustaining, they end up striking the anode.

Meanwhile, the much larger & denser necleii of the electron-stripped atoms are not drawn through the arc with as much speed, any many end up dissipating into the surrounding gas, rather than impacting the cathode.

Due to this imbalance in the impacts of energetic particles, the vast majority of arc-caused heating to the electrodes occurs on the anode.

For more explanation, here is a detailed and informative article from lincolnelectric.com, explaining some of the various properties & arrangements of this tranferrance which are exploited in the verious metal arc-welding processes.